Volume 4 Aircraft equipment and
Chapter 2 All weather terminal area operations
Section 1 Introduction
4-146 ORGANIZATION AND OVERVIEW OF CHAPTER 2. The description
of All Weather Terminal Area Operations (AWTA) and the approval process
are divided into 11 sections:
· Section 1 introduces AWTA, providing an overview of concepts
and evolution of AWTA, as well as various factors affecting AWTA. This
section is historical and conceptual information only. For specific
authorizations and requirements, see the following sections;
· Section 2 provides the five-step process for operator
approval to conduct Category (CAT) II/III operations (except small Category
· Section 3 provides an approval process for conducting
CAT II operations in small Category A aircraft under Title 14 of the
Federal Code of Regulations (14 CFR) part
· Section 4 provides guidance for Surface Movement Guidance
and Control Systems (SMGCS), including operator requirements and airport
authorization by All Weather Operations Specialists (AWOS);
· Sections 5–7 provide respective overviews of CAT I, CAT
II, and CAT III operational requirements;
· Section 8 provides specific approval guidance for 14 CFR part
· Section 9 provides specific approval guidance for special
instrument approach procedures (IAP);
· Section 10 provides specific approval guidance for maintenance
and inspection programs for low visibility approach landing minimums;
· Section 11 provides an introduction to Performance-Based
4-147 GENERAL BACKGROUND. AWTA include all terminal area
operations conducted under instrument flight rules (IFR), including
certain operations conducted in visual conditions. Terminal area operations
conducted under visual flight rules (VFR) in visual weather conditions
are not addressed in this chapter. This chapter discusses concepts,
national direction, and guidance to be used by Federal Aviation Administration
(FAA) inspectors when evaluating, approving, or denying requests for
authorization to conduct AWTA operations. This chapter also covers operational
approvals for an operator proposing to use new aircraft, AWTA operating
systems, lower-than-standard takeoff minimums, and approach and landing
operating minimums. The basic principle for AWTA takeoff, approach,
and landing operations is that operating minimums are permitted to be
reduced through improvements in operational capabilities. This principle
is valid only if an acceptable alternative maneuver is maintained or
if an extremely high probability of safely completing the maneuver exists.
All IAPs are constructed to permit safe instrument flight to the missed
approach point (MAP), followed by an instrument missed approach. The
safety of conducting an instrument approach to a published minimum and
executing the missed approach is not dependent on establishing visual
reference with the landing surface. The criteria for constructing an
instrument approach are based on the premise that an instrument missed
approach will be necessary under certain circumstances. Visual reference
with the landing surface, however, becomes a safety factor when the
flight descends below the published IFR minimum height or altitude.
The visibility or Runway Visual Range (RVR) minimum for a particular
runway becomes a safety consideration in both fuel planning and selection
of alternate airports.
A. AWTA. AWTA in domestic and international operations are
complex, with many variations in aircraft and ground equipment, as well
as procedures and standards. FAA inspectors must evaluate proposed AWTA,
giving due consideration to the following:
· Operator’s type of operation 14 CFR part (
91 subpart F,
91 subpart K (91K),
129, and 135—fixed-wing or helicopter);
· Type of proposed AWTA (takeoff, landing, etc.);
· Type of operator’s aircraft and equipage;
· Airports proposed for use;
· Operating minimums proposed; and
· Operator’s experience, both in similar or other aircraft,
and in the type of operation proposed.
B. Specific Standards. Specific standards are provided in this chapter
to evaluate operations using aircraft and equipment that have well-understood
operational characteristics and limitations in specific AWTA. When an
operator requests approval to conduct operations not covered by these
standards, or when an operator requests to use lower operating minimums
than provided by these standards, the request must be forwarded to the
regional Flight Standards division (RFSD) Next Generation (NextGen)
Branch (AXX-220). AXX-220 will coordinate with the Flight Technologies
and Procedures Division (AFS-400) to develop any additional necessary
AWTA operational concepts.
C. Authority and Responsibility for Approval of AWTA.
1) The complex nature of AWTA in domestic and international
environments, the wide variation of airborne and ground-based equipment,
and the variation in procedures and standards used in these operations,
require a broad-based evaluation and approval process. Due to operational
and technical complexities, it is essential for this evaluation and
approval process to use a systems approach (big picture approach).
2) This systems approach must involve many personnel who are
knowledgeable in their respective areas. When the safety of a proposed
operation is being evaluated, personnel knowledgeable in such areas
as aircraft certification, instrument landing system (ILS)/microwave
landing system (MLS) ground equipment design and maintenance, visual
aid concepts and criteria, IAP design criteria, airport design criteria,
flight inspection, air traffic control (ATC) procedures, flight operational
programs, and aircraft maintenance programs must be involved.
3) This broad-based systems approach process is particularly
important in the evaluation and approval of CAT II and CAT III approach
and landing operations. Although approval of CAT I operations is relatively
straightforward due to the high level of CAT I operational experience
and international standardization, CAT II and CAT III operations must
be examined and approved on a runway-by-runway and an operator-by-operator
4-148 EVOLUTION OF AWTA. In the early years of aviation, all flight
operations were conducted in visual flight conditions. During those
early years, electronic ground-based Navigational Aids (NAVAID) were
not available and cockpit instrumentation could not support flight in
instrument meteorological conditions (IMC). The capability of AWTA slowly
evolved as flight instrumentation, airborne navigation equipment, and
ground-based electronic NAVAIDs were developed and improved. The development
of the gyroscope established the foundation for instrument flight. The
essential information provided by the gyroscope permitted pilots to
safely control aircraft during instrument flight conditions. Operating
minimums were gradually reduced as overall capability for instrument
flight improved. The introduction of turbojets for commercial service
in 1958 provided the stimulus for further and more rapid refinement
of equipment, operating procedures, and standards. For the first 3 ½
years, turbojet operating minimums for approaches with vertical guidance
(called precision approaches) were specified as a ceiling of 300 feet
and visibility of three-fourths statute mile. These early minimums were
modified to a decision height (DH) of 200 feet and a visibility of three-fourths
statute mile (RVR 4000), and became known as the “basic turbojet minimums.”
Included as part of the initial concept of operating minimums was an
increase in the operating minimums for air carrier pilots in command
(PIC) until 100 hours of flight experience in a particular type of aircraft
was obtained. This was determined by adding 100 feet to the published
ceiling and one half statute mile to the published visibility for each
approach. This aspect of the concept of operating minimums is still
in use today. The high-minimum PIC requirement is currently specified
in parts 91K,
135 (with RVR landing minimum equivalents in the operations specification
4-149 BASIC TYPES OF AWTA APPROACH AND LANDING OPERATIONS.
There are two general classes of approach and landing operations: those
conducted under VFR, and those conducted under IFR. There are three
basic types of IFR approach and landing operations: visual approaches,
contact approaches, and instrument approaches.
A. Visual Approaches. A visual approach can be authorized
by ATC if the aircraft is being operated under IFR in visual meteorological
condition (VMC) (reported weather at airport must have ceiling at or
above 1000 feet and visibility 3 miles or greater). Although a pilot
conducting a visual approach is expected to proceed to the destination
airport by pilotage or visual reference to another aircraft, the flight
remains under an instrument flight plan. ATC retains responsibility
for both traffic separation and wake/vortex separation, unless the pilot
reports the preceding aircraft in sight and is instructed to follow
it. ATC will provide flight-following and traffic information until
the aircraft is instructed to contact the control tower. Either ATC
or the pilot may initiate a request for a visual approach.
NOTE: Charted visual flight procedures (CVFP), a subset of visual
approaches, are also considered to be visual approaches.
B. Contact Approach. A contact approach can only be authorized
by ATC when requested by the pilot. The flight must be operated clear
of clouds, the pilot must have at least 1 mile of flight visibility,
and can reasonably expect to be able to continue to the airport in those
conditions. The pilot must be on an IFR flight plan, and the ground
visibility at the destination airport must be reported to be at least
1 statute mile. A contact approach is an approach procedure that may
be used by a pilot (with prior ATC authorization) instead of a published
Standard Instrument Approach Procedure (SIAP) or special IAP. ATC will
not authorize a contact approach at an airport that does not have a
functioning IAP. Although ATC provides separation services to a flight
during a contact approach, the pilot must assume full responsibility
for obstacle clearance and navigation to the destination airport.
C. Instrument Approaches. IAPs are provided to permit descent
in instrument conditions from the en route environment to a point where
a safe landing can be made at a specific airport.
1) The types of SIAPs include the following approaches based
on International Civil Aviation Organization (ICAO) standard NAVAIDs,
such as an ILS, MLS, Global Positioning System (GPS), very high frequency
(VHF) omnidirectional range (VOR), and non-directional radio beacon
(NDB). IAPs using these NAVAIDs may require, or may be supplemented
by, use of distance measuring equipment (DME).
2) In addition to NAVAID IAPs, there are also IAPs based on
ATC radar services such as airport surveillance radar (ASR) and precision
approach radar (PAR). SIAPs also include Performance-based Navigation
(PBN) procedures that are developed in accordance with U.S. Terminal
Instrument Procedures (TERPS) or ICAO Procedures for Air Navigation
Services Aircraft Operations (PANS-OPS).
3) Area Navigation (RNAV) and Required Navigation Performance
(RNP) concepts are consistent with the performance characteristics of
systems such as GPS, DME/DME/Inertial Reference Units (IRU), GPS/DME/DME/IRU,
or flight management system (FMS)/GPS, or FMS/GPS/IRU.
D. Lighting System Credits. All straight-in operating
minimums are based on the use of ground-based visual aids to enhance
seeing‑conditions during the final stages of approach and landing operations
(deceleration for helicopters). These reductions are known as lighting
system credits and cannot be used to reduce operating minimums for circling
maneuvers due to the large area required for safe maneuvering (turn
radius) at the various speeds used. Therefore, operating minimum reductions
based on lighting credits can only be authorized for instrument approaches
to runways that provide a straight-in landing capability. The standard
minimum IFR altitudes cannot be reduced due to obstacle limitations,
NAVAID signal limitations, and/or navigation system limitations. As
such, reductions in operating minimums below the basic values established
for each type of approach are expressed only as reductions in the visibility/RVR
required to safely conduct the approach. The minimums for the various
navigation systems and lighting system combinations are specified in
the current edition of Order 8260.3, Terminal Instrument Procedures
4-150 EVOLUTION OF CAT I OPERATIONS.
A. Achieving Current CAT I Operating Minimums. Initial
steps toward achieving current CAT I operating minimums began on September
28, 1961. These original developments became the foundation for the
“building block” approach leading to further reductions in operating
minimums. The first air carrier operator met these requirements on May
11, 1962, enabling it to utilize the new reduced minimums of a 200-foot
ceiling and ½-statute mile visibility (RVR 2600). The minimums reductions
were based on meeting all of the following requirements:
1) Ground-based NAVAIDs:
· A complete, operational ILS.
· A maximum glideslope angle of 3 degrees.
2) Ground-based visual aids:
· High Intensity Runway Lights (HIRL).
· Full configuration approach lights with sequenced flashing
· All-weather runway marking or runway centerline (RCL)
3) Airborne equipment:
· A flight director (FD) system or an automatic approach
coupler (autopilot (AP)).
· An instrument failure warning system or cockpit procedures
for assuring the immediate detection of instrument failures or malfunctions.
4) PIC experience, training, and qualification:
· One hundred hours of experience as PIC in the particular
type of turbojet or turbine-powered airplane.
· Raw data approach to 200 feet.
· FD and/or AP approach to 100 feet.
· ILS approach (FD and/or AP as appropriate) to 100 feet,
followed by a landing.
· Engine-out ILS approach to a landing or missed approach.
5) Additional runway field length and crosswind component limitations:
· Fifteen percent or 1,000 feet of additional field length
(whichever is greater) over normal regulatory requirements.
· Maximum crosswind component was 10 knots.
B. Specifying the Operating Minimums. A major change
in the method of specifying the operating minimums for approaches with
vertical guidance evolved with the introduction of the DH and RVR concepts.
These changes were finalized by the publication of U.S. TERPS criteria
in 1966. This conceptual change eliminated the ceiling requirement by
introducing a DH. This conceptual change was necessary because of the
limitations in the methods used to observe or measure ceiling and visibility.
Often ceiling and visibility observations were taken several miles from
the approach end of a runway, and as a result were frequently not representative
of the seeing‑conditions encountered during the final stages of an approach
and landing, especially in rapidly changing or marginal weather conditions.
Operational use of RVR reports began in 1955, but they were not available
at most major airports until the early 1960s. Since 1989, all approach and landing operations using minimums below ½-statute mile
visibility have been based on RVR reports.
C. Reduced Operating Minimums. In 1963, operating minimums were
reduced further to DH 200/RVR 1800 for two- and three-engine airplanes
(usually Category B or C) and DH 200/RVR 2000 for four-engine airplanes
(usually Category D). These reductions were based on the “building block”
approach established in 1961 and the added requirement for enhanced
in-runway lighting systems such as high-intensity touchdown zone (TDZ)
and RCL lighting. In 1964, the minimums for runways not equipped with
TDZ and RCL lights were reduced to DH 200/RVR 2400. Improvements in
visual aids were and remain critical in reducing landing minimums. These
aids provide pilots with the necessary external visual references for
manually controlling and maneuvering the aircraft during the final approach,
flare, landing, and taxiing. The requirement for improvements in the
overall airborne and ground-based equipment capabilities, combined with
a cautious incremental reduction in operating minimums, ensured that
a high level of safety was maintained.
D. Common CAT I Operating Minimums for Aircraft Categories
A–D. In 1988, CAT I operating minimums for Category D airplanes
were reduced to DH 200/RVR 1800. This change established common CAT
I minimums for all airplanes. The 1988 reduction was based on more than
20 years of successful experience with Category B and Category C turbojet
aircraft operating to DH 200/RVR 1800, as well as research and analysis.
This research has shown that the handling characteristics and seeing‑conditions
in existing turbojet Category D airplanes were equivalent to other turbojets.
E. Lowest CAT I Operating Visibility Minimums.
1) In 2006, the lowest CAT I operating visibility minimums were
revised to harmonize these minimums with the European Aviation Safety
Agency (EASA). The majority of harmonized visibility minimums were based
on a geometric calculation using the glidepath angle (or published vertical
angle), height above threshold (HATh), and length of instrument approach
lighting using the following formula: RVR = (HATh ÷ tangent glidepath
angle) - length of instrument approach lighting.
2) Standard lengths for four categories of instrument approach lighting
were based on the minimum lengths of lighting systems in each category.
RVRs for 200 feet HATh were calculated using a glidepath angle of 3
degrees. RVR values were restricted to a minimum of 1800 to retain operationally
proven minimum RVRs. Use of visibility minimums below RVR 2400 requires
operative TDZ and RCL lighting or use of an approved head-up display
(HUD), FD (except single-pilot), or AP coupled approach to DH.
3) In 2009, FAA Order
8400.13, Procedures for the Evaluation and Approval of Facilities
for Special Authorization Category I Operations and All Category II
and III Operations, provided the criteria for Special Authorization
(SA) CAT I approaches with a DH as low as 150 feet (HATh using radio
altimeter (RA) minimums) and a visibility minimum as low as RVR 1400
at runways with reduced lighting, provided an approved CAT II or CAT
III HUD is used to DH.rocedures for the Evaluation and Approval of Facilities
for Special Authorization Category I Operations and All Category II
and III Operations, provided the criteria for Special Authorization
(SA) CAT I approaches with a DH as low as 150 feet (HATh using radio
altimeter (RA) minimums) and a visibility minimum as low as RVR 1400
at runways with reduced lighting, provided an approved CAT II or CAT
III HUD is used to DH.
4-151 EVOLUTION OF CAT II OPERATIONS.
A. The Concepts and Criteria. The concepts and criteria
established in the early 1960s were the building blocks for all CAT
II and III operations. The initial criteria for CAT II operations were
issued in October 1964. These criteria resulted in a requirement for
further improvements in ground-based NAVAIDs, RVR reporting capabilities,
airborne equipment, maintenance standards, and pilot training and qualification.
Current CAT II criteria are essentially the same as those issued in
1964, except for enhancements to provide additional flexibility and
operational credit for modern flight control systems.
B. Guidance During CAT II Operations. During CAT II operations,
greater reliance must be placed on the guidance provided by the ground-based
NAVAIDs. Therefore, design and maintenance criteria for airborne and
ground-based equipment must ensure that better performance and higher
reliability are achieved by the total system. For example, before an
airport can qualify for CAT II minimums, it must be equipped with an
ILS that has greater signal quality, reliability, and integrity. It
is also necessary for CAT II runways to have more than one RVR reporting
system to provide more accurate information concerning seeing‑conditions
on the runway. A purpose of these requirements is to supplement the
TDZ and RCL lighting required for operations below RVR 1800. Additional
airborne equipment is also required, as follows:
· Dual ILS localizer and glideslope receivers.
· An autocoupler (AP) and an FD system, or two independent
· Equipment to identify the DH (such as a RA).
· Rain removal equipment.
· Go-around guidance.
· An autothrottle system (for certain aircraft to reduce
C. Initial CAT II Criteria. Initial CAT II criteria were established
to provide flexibility to operators in choosing various combinations
of airborne equipment to meet CAT II requirements. An operator had to
prove (demonstrate) that the performance and reliability of their selected
airborne system performed, and continued to perform, at the level of
precision and reliability required for CAT II operations. The pilot
training and qualification program, through enhanced ground and flight
training, also had to provide the pilot proficiency required. This program
had to address factors such as the availability and limitations of visual
cues in the CAT II environment, as well as the procedures and techniques
for transitioning from non-visual to visual flight at low altitude during
D. Type Design Approval Standards for CAT II. CAT II
type design approval standards had not been established during initial
CAT II operations. As a result, the following methods were established
to achieve airborne equipment approval:
1) Operational Demonstration. When the operator’s airborne equipment
had not been certificated (type design approved) for CAT II operations,
the operator was permitted to establish an extensive operational demonstration
program. The purpose of this program was to show that the required levels
of performance and reliability were attained and maintained. This program
consisted of numerous approaches (approximately 300). The operator was
also required to show that the methods for failure and/or malfunction
detection were acceptable to the Administrator.
2) Type Design Approval. When the operator could show that the
airborne equipment had been previously tested and expressly approved
for CAT II operations during FAA type certification (TC) or Supplemental
Type Certification (STC), the operator was not required to conduct as
extensive an operational demonstration before receiving initial CAT
E. Demonstrating that all Initial Criteria had Been Met. When an
operator had demonstrated that all of the initial criteria had been
met, initial operations to DH 150/RVR 1600 were authorized. This authorization
was known as an “operational approval.” Operational approvals were accomplished
by the issuance of standard OpSpecs. Following this initial operational
approval, the operator was required to demonstrate the ability to maintain
the required levels of reliability and performance on a continuing basis
in CAT II line operations. After 6 months, assuming continued satisfactory
maintenance and performance of the airborne systems, the operator was
issued an operational approval to operate with minimums of DH 100/RVR
1200. These basic CAT II criteria for approval are still applicable
today but the lowest authorized RVR minimums currently is 1000.
F. CAT II Operations Other than ILS. The only types of
CAT II operations that can be currently authorized for use by U.S. operators
are ILS-based operations or SA for certain CAT II operations at specifically
approved facilities. MLS-based CAT II operations, however, could be
conducted in the future at a few locations, provided the operation is
restricted to an ILS-like operation that has at least a 5-nautical mile
(NM) straight-in Final Approach Segment (FAS). The flight control laws
(computational logic) used in most existing FDs and APs require that
an FAS be at least this long to perform its intended functions in CAT
II operations. Most existing flight control guidance systems will have
to be modified and recertificated before CAT II MLS operations with
a short FAS can be conducted. This action is necessary for CAT II operations
with segmented and/or curvilinear approach paths that result in straight-in
FASs that are significantly less than 5 NM. Usually this action will
include equipment modifications, type design approval, an extensive
engineering analysis, and a flight test program. Certain new aircraft,
however, might be configured with the necessary equipment and certificated
for segmented approach paths, curvilinear approach paths with very short
straight-in final approach courses, or both.
4-152 EVOLUTION OF CAT III OPERATIONS.
A. Initial Step in Introducing CAT III Operations. In
1966 at an ICAO Communications/Operations (COM/OPS) divisional meeting,
international CAT III ground and airborne equipment standards were established
that were essential to further development of ground and airborne equipment
and operating concepts.
B. Initial U.S. CAT IIIa Criteria. The initial U.S. CAT
IIIa criteria (see the current edition of Advisory Circular (AC)
120-28, Criteria for Approval of Category III Weather Minima
for Takeoff, Landing, and Rollout) were issued on September 5, 1969,
to assist industry in developing a CAT IIIa capability. These criteria
were based on the CAT I and CAT II building blocks, and further improvements
were required in ground-based NAVAIDs, RVR reporting capabilities, airborne
equipment (such as a requirement for autoland), maintenance standards,
and pilot training and qualification. These initial criteria did not
include definitive operational approval requirements for ground support
systems, maintenance, training, and operational procedures and limitations.
However, the basic concepts and the minimum airborne equipment type
design requirements considered necessary for CAT IIIa operations were
clearly delineated in AC
120-28. These basic concepts and equipment requirements included
· Alert height (AH) concept.
· Fail passive (FP) flight control system concept.
· Fail operational (FO) CAT IIIa system concept.
· Autoland concept.
· Dual radio (radar) altimeter requirements.
· Redundant flight control system requirements.
· Enhanced missed approach instrumentation.
· Autothrottle control system requirements.
· Enhanced failure detection and warning capability.
· Type design approval criteria.
NOTE: “Fail operational” means an airborne system with redundant
operational capability down to touchdown and, if applicable, through
rollout. The redundant operational systems must have no common failure
modes. If one of the required systems fails below AH, the flare, touchdown,
and rollout, if applicable, can be accomplished using the remaining
operational system or systems. “Fail passive” means an automatic flight
control system (AFCS), which, upon occurrence of any single failure,
should not cause: significant displacement from the approach path, altitude
loss below the nominal glidepath, or (upon disconnection) involve any
significant out-of-trim condition. In addition, any single failure should
not cause any action of the flight control system that is not readily
apparent to the pilot. See AC 120‑28.
C. Initial CAT IIIa Approvals. The publication of initial
CAT IIIa criteria (AC
120-28) led to the rapid development of CAT IIIa airborne and ground-based
capabilities. In February 1971, the B-747 was granted the first U.S.
type design approval for CAT IIIa. This type design approval was based
on the use of FO automatic landing systems. CAT IIIa criteria were significantly
improved in December 1971, by the publication of AC
120-28A. This revision enhanced the type design (airworthiness
certification) approval criteria, and established initial operational
approval criteria. Washington-Dulles Airport received the first U.S.
CAT IIIa ILS facility approval in January 1972. The type design for
the L-1011 was certificated for CAT IIIa using FO autoland systems in
April 1972. The first U.S. CAT IIIa operational approval was issued
to Trans World Airlines on September 15, 1972, for FO CAT IIIa operations
using the L-1011. All initial CAT IIIa operations were restricted to
Type III ILS equipped runways and FO CAT IIIa airborne equipment.
D. Type II ILS-Equipped Runways and FP Airborne Equipment.
The criteria initially established for CAT IIIa (AC
120-28) were based on a conservative approach for reducing operating
minimums. However, with additional operational experience, it was determined
that the initial criteria were unnecessarily stringent.
1) After a thorough review of the Type II ILS equipment, the
FAA determined that some Type II installations could be upgraded with
minor modification to support CAT IIIa operations. Furthermore, the
operational experience of Air Inter in France during extensive CAT III
operations (RVR 500) using FP autoland systems indicated that under
tightly controlled conditions FP CAT III operations could be safely
conducted. Research efforts in the United States and Europe also supported
2) In October 1976, Notice N 8400.18, Job Function Reference
guide for Air Carrier Safety Inspectors (OPERATIONS), was issued to
establish approval criteria for FP CAT IIIa autoland operations using
DH 50/RVR 700. In December 1976, the B-727 became the first airplane
certificated by the U.S. for FP CAT IIIa operations. AC 120-28B, issued in December 1977, permitted CAT IIIa operations
at runways equipped with suitably modified Type II ILS equipment. It
also permitted FP autoland operations with aircraft having handling
characteristics, physical characteristics, and seeing‑conditions equivalent
to the B-727 and DC-9 airplanes.
3) A Flight Standards Service (AFS) policy decision, expressed in a letter
dated June 22, 1978, authorized CAT IIIa operations to 32 runways equipped
with Type II ILS equipment at 31 airports. FAA Order 8400.8, Procedures
for the Approval of Facilities for 14 CFR part
121 and part
135 Cat III Operations, was initially issued on September 10, 1980,
to enhance the criteria and procedures for approving CAT III operation
using U.S. Type II ILS facilities. These changes significantly increased
the number of facilities that could support CAT IIIa operations and
the number of aircraft that could potentially use these facilities.
4) As of 2010, all systems supporting CAT II or CAT III operations
(Mark 20 systems) meet the integrity requirements of a Type III system.
The lowest landing minimums currently (2010) authorized for CAT IIIa
by U.S. operators at any airport is RVR 700. Consideration is being
given to reducing the minimum RVR to 600 in order to harmonize U.S.
CAT IIIa standards with ICAO.
E. Initial CAT IIIb Criteria. As operational experience
and capability of airborne equipment increased in CAT IIIa operations,
the need for CAT IIIb criteria was gradually realized. Initial U.S.
CAT IIIb criteria were issued in March 1984 (AC
120-28C). This revision permitted operations with minimums as low
as RVR 300. The B-767 became the first aircraft certificated (type design
approval) for CAT IIIb by the United States. The B-767 was approved
under a final draft version of that AC. The initial CAT IIIb criteria
were based on the CAT I, CAT II, and CAT IIIa building blocks.
1) Further enhancements were required in the CAT IIIb criteria,
particularly in ground-based NAVAIDs, lighting systems, RVR reporting
systems, airborne equipment, and training and qualification programs.
These revisions further clarified CAT III operational concepts, system
requirements, and the visual references necessary for the various CAT
III operations. Another conceptual change was implemented by establishing
concepts for CAT III operations with the “pilot in the active control
loop.” These new concepts permitted manually flown CAT III operations
using special flight guidance and control systems such as HUDs.
2) The first U.S. CAT IIIb operational approvals were granted
to Trans World Airlines (L-1011) and Eastern Airlines (L-1011 and A300)
using minimums of RVR 600. RVR 600 was the lowest minimum supported
by U.S. facilities due to RVR reporting system limitations. The first
CAT IIIb RVR 300 minimum approvals were granted to Delta and Eastern
Airlines in September 1984, for L-1011 aircraft. Initial RVR 300 approvals
were restricted to those airports equipped with CAT III taxiway RCL
lights and the capability to report RVRs as low as RVR 300. The first
U.S. CAT IIIb RVR 300 ILS facility approval was granted for runway 16R
at Seattle-Tacoma International Airport (SeaTac) in 1987.
4-153 CURRENT CATEGORIES OF IAPs. Various categories of instrument
approach operations have been established to accommodate a wide variety
of airborne and ground- or space-based capabilities. These operational
categories are necessary for granting credit to operators choosing to
install airborne equipment with additional capabilities. These operational
categories also provide the distinction between operational capabilities
and ground support system configurations. CAT I, CAT II, and CAT III
are the three basic categories of instrument approach operations.
A. CAT I Operations. CAT I operations are defined as
precision approach and landing operations conducted under IFR using
CAT I operating minimums. CAT I operating minimums consist of a specified
IFR decision altitude (DA)/decision height (DH) that is not lower than
the equivalent of 200 feet (60 meters) above the TDZ, and a visibility,
Runway Visibility Value (RVV), or an RVR that is not lower than one-half
statute mile or RVR 1800, respectively.
B. SA CAT I.
8400.13 authorizes SA CAT I approaches to an RA DH as low as 150
feet and a visibility minimum as low as RVR 1400 to runways that do
not have TDZ or RCL lighting when the approach is flown using an aircraft
with a HUD to DH.thorizes SA CAT I approaches to an RA DH as low as
150 feet and a visibility minimum as low as RVR 1400 to runways that
do not have TDZ or RCL lighting when the approach is flown using an
aircraft with a HUD to DH.
C. Standard CAT II Operations. CAT II operations are
approach and landing operations conducted with a DH of less than 200
feet (60 meters) but not less than 100 feet (30 meters), and an RVR
of not less than 1,200 feet (350 meters).
D. CAT II RVR 1000.
8400.13 authorizes CAT II approaches with a DH as low as 100 feet
and visibility minimums of RVR 1000 to runways that meet all CAT II
equipment, performance, and lighting requirements. The operator must
use either autoland or HUD to touchdown.thorizes CAT II approaches with
a DH as low as 100 feet and visibility minimums of RVR 1000 to runways
that meet all CAT II equipment, performance, and lighting requirements.
The operator must use either autoland or HUD to touchdown.
E. SA CAT II.
8400.13 authorizes CAT II approaches with a DH as low as 100 feet
and visibility minimums of RVR 1200 at runways that do not meet all
of the lighting requirements (Approach Lighting System with Sequenced
Flashing Lights (ALSF)-2, TDZ, RCL lights) for standard CAT II. The
operator must use either autoland or HUD to touchdown.thorizes CAT II
approaches with a DH as low as 100 feet and visibility minimums of RVR
1200 at runways that do not meet all of the lighting requirements (Approach
Lighting System with Sequenced Flashing Lights (ALSF)-2, TDZ, RCL lights)
for standard CAT II. The operator must use either autoland or HUD to
F. CAT III Operations. CAT III operations are separated
into three subcategories: CAT IIIa, CAT IIIb, and CAT IIIc.
1) CAT IIIa Operations. CAT IIIa is an approach and landing
operation with an RVR of not less than 700 feet (200 meters) without
a DH, or with a DH of less than 100 feet (30 meters), or an AH that
is typically between 50 and 200 feet, depending on aircraft certification
and operator preferences. Both FP and FO airborne equipment can be used
in CAT IIIa operations.
2) CAT IIIb Operations. CAT IIIb is an approach and landing
operation with an RVR of less than 700 feet (200 meters) but not less
than 150 feet (50 meters) and a DH of 50 feet (15 meters) or less, or
an AH which is typically between 50 and 200 feet, depending on aircraft
certification and operator preferences. Both FP and FO airborne equipment
can be used for CAT IIIb operations.
3) CAT IIIc Operations. CAT IIIc is an approach and landing
operation without a DH and without RVR limitations (zero-zero). CAT
IIIc operations are currently not authorized.
1) SIAPs that are published in accordance with 14 CFR part
97 without Authorization Required (AR) or Special Aircrew
and Aircraft Certification Required (SAACR) restriction are approved
for all users of the U.S. National Airspace System (NAS) and are incorporated
in the standard OpSpecs by reference.
2) If an IAP is published in part
97 and designated as an AR or SAACR procedure, it is only available
to those operators, aircraft, and aircrews that meet the special qualification
requirements for that procedure and that are approved to use it. An
IAP is a series of predetermined maneuvers for the orderly and safe
transfer of an aircraft under instrument flight conditions, from the
beginning of the initial approach to one of the following:
· An automatic landing.
· A position from which a landing can be made visually.
· A position from which a missed approach can be executed
and completed if external visual references necessary to complete the
landing are not established before passing DA/DH or minimum descent
B. IAPs and Its Operating Minimums. An instrument approach
and its operating minimums are usually prescribed and approved for a
specific airport and/or runway by the aviation authority (AA) that has
jurisdiction over flight operations at that airport. The FAA is responsible
for developing all civil IAPs and for specifying the operating minimums
for all IAPs in the United States, its territories, and the U.S. Army
IAPs worldwide. In the case of other military IAPs, an instrument approach
and its operating minimums are prescribed and approved for a specific
airport and/or runway by the authority having jurisdiction over flight
operations. There are various types of IAPs that are or may be approved
for use by U.S. air carriers. These types of IAPs include the following:
· IAPs published in accordance with part
· IAPs authorized in OpSpecs.
· FAA-approved special IAPs (FAA Form 8260-7, Special Instrument
· Department of Defense (DOD) IAPs at U.S. military airports.
· IAPs published by a foreign country.
· IAPs developed by an air carrier in a foreign country
in accordance with the current edition of FAA Order
8260.31, Foreign Terminal Instrument Procedures.oreign
Terminal Instrument Procedures.
C. CVFPs. Even though CVFPs are available for public
use by aircraft on IFR flight plans, they are not standard Instrument
Flight Procedures (IFP). Except for CVFPs, it may be assumed that any
SIAP charted in a U.S. Government Flight Information Publication (FLIP)
is appropriately published in part
4-155 OTHER IAPs. If, however, an IAP and its operating
minimums are not published in accordance with part
97, other means have been established to authorize their use. In
such cases, the IAP is incorporated into standard OpSpecs by reference
(either with or without additional restrictions). This group of instrument
procedures that are not published in part
97 includes IAPs developed by the FAA, third party developers, certain
U.S. military organizations, foreign governments, air carriers, and
IAPs based on nonstandard NAVAIDs such as Tactical Air Navigational
Aid (TACAN), Tactical Landing Approach Radar (TALAR), airborne radar,
or commercial broadcast stations. Many of these approach procedures
are not available to all users due to the location, special training,
knowledge, or equipment required to safely conduct them.
A. U.S. Military IAPs. U.S. military IAPs are approved
by the local base commander and published by the DOD. Since these procedures
comply with U.S. TERPS criteria, U.S. military IAPs must be used by
air carriers when operating at military airports, unless the procedure
is noted “Not for Civil Use” by the military. IAPs published by the
DOD for U.S. military airports are incorporated into the standard OpSpecs
B. Foreign Government IAPs. At foreign airports, the
authority having jurisdiction over flight operations at the airport
establishes the IAPs and their operating minimums. In general, the IAPs
and operating minimums (if specified) at most foreign airports are developed
in accordance with U.S. TERPS or ICAO PANS-OPS criteria. IAPs developed
by foreign authorities using TERPS or PANS-OPS are approved for use
by U.S. air carriers in accordance with FAA Order
8260.31 and are incorporated in the standard OpSpecs by
reference. In some cases it may be necessary to restrict certain foreign
IAPs to make them equivalent to U.S. or ICAO criteria. FAA Order 8260.31
provides direction and guidance for restricting such foreign IAPs. When
a restriction to a foreign IAP is required, it must be specified in
OpSpec C058.d are incorporated in the standard OpSpecs by reference.
In some cases it may be necessary to restrict certain foreign IAPs to
make them equivalent to U.S. or ICAO criteria. FAA Order
8260.31 provides direction and guidance for restricting
such foreign IAPs. When a restriction to a foreign IAP is required,
it must be specified in OpSpec C058.ovides direction and guidance for
restricting such foreign IAPs. When a restriction to a foreign IAP is
required, it must be specified in OpSpec C058.
C. IAPs Developed by an Air Carrier. At some foreign
airports, an air carrier may need to develop or choose to develop an
IAP. The standard OpSpecs enable an air carrier to exercise this option,
provided the developed procedure meets either U.S. TERPS or ICAO PANS-OPS
criteria. In such cases, the IAP developed by the air carrier may be
authorized for use by listing it in OpSpec C081, provided the air carrier
submits appropriate supporting information in accordance with FAA Order
8260.31. These procedures may be based on either public
or private NAVAIDs.hese procedures may be based on either public or
D. Non-Federal NAVAIDs. Non-Federal NAVAIDs can be used
for public and special IAPs. Approval for the use of these NAVAIDs within
the NAS is established in the current edition of Order 6700.20A, Non-Federal
Navigational Aids and Air Traffic Control Facilities, and 14 CFR part
171. An inspector should become familiar with these
documents before issuing approval to use these IAPs. Approval to use
special IAPs based on non-Federal NAVAIDs is accomplished by listing
them in OpSpec C081.
E. Commercial Broadcast Station IAPs. In the past, limited
authorizations to use commercial broadcast stations have been granted
in unique situations. The need for these procedures has been steadily
declining because of the increased availability of standard NAVAIDs.
In general, new approach procedures based on commercial broadcast stations
will not be approved. In any case, AFS-400 review and concurrence must
be obtained before an inspector may approve an IAP based on commercial
F. Special IAPs. Special IAPs are those procedures evaluated
and approved by the FAA but not published in accordance with part
97. These special IAPs are not approved for general use due to the
special training, private facilities, procedures, knowledge, and/or
equipment required to safely conduct them. Due to these special requirements,
the use of special IAPs must be authorized on an operator-by-operator
basis. Special IAPs are issued on FAA Form 8260-7 and authorized in
G. IAPs Outside of Controlled Airspace. Since ATC separation
services are an important element of safe instrument approach operations,
special consideration and evaluation is required before operations can
be authorized outside of controlled airspace (no ATC separation services
available). This situation occurs when conducting an IAP at an airport
that is in Class G airspace (e.g., does not have an operating control
tower or when a control zone is not active). The airports, at which
portions of IAPs are outside of controlled airspace, must be authorized
by the standard OpSpec C064.
H. Airborne Radar Approaches (ARA). ARAs are based on
the use of airborne radar. Within the United States, ARAs are classified
as special IAPs and are established by the issuance of FAA Form 8260-7.
Use of ARAs can be authorized through standard OpSpecs if the criteria
in the current edition of AC
90-80, Approval of Offshore Standard Approach Procedures, Airborne
Radar Approaches, and Helicopter En Route Descent Areas, and this order
I. Offshore Standard Approach Procedures (OSAP). OSAPs
are helicopter specials that are designed for use to offshore platforms.
OSAPs are based on the use of GPS and the airborne radar systems and
are established and approved in accordance with the criteria in AC
90-80. These special procedures are developed for individual
operators and are issued and authorized through OpSpecs, management
specifications (MSpecs), or letters of authorization (LOA).
4-156 CONSIDERATIONS FOR APPROACH AND LANDING OPERATIONS.
U.S. TERPS contains the established minimum criteria for standard IAPs
within the U.S. NAS. PANS-OPS, Volume II contains the established minimum
criteria for IAPs in most foreign countries. These criteria allow for
safe instrument approach and landing capabilities for aircraft equipped
with ICAO standard NAVAIDs (ILS, GPS, VOR, VOR/DME, and NDB) and performance-based
approaches based on RNP concepts. Many operators have chosen to use
airborne equipment exceeding the minimum capabilities required for instrument
flight. A means of granting operational credit for using equipment with
these increased capabilities has been established. The standard OpSpecs
provide the method to approve approach and landing operations using
such airborne equipment. Examples of airborne equipment with increased
capabilities include automatic landing systems (autoland) and manually
flown electronic landing systems (HUD), ARA systems, and RNAV systems
with RNP and RNP AR capabilities. The following subparagraphs briefly
discuss these systems.
1) Autoland Approach. An autoland approach is an instrument
approach to touchdown, and in some cases, through the landing rollout.
An autoland approach is performed by the aircraft AP, which is receiving
position information and/or steering commands from onboard navigation
equipment. Autoland approaches are flown in VFR and IFR. It is a commonly
accepted safe operating practice for operators to require their aircrews
to fly coupled approaches and autoland approaches (if certified) on
suitable runways when the weather conditions are less than approximately
2) Automatic Landing Systems. As an example of modern airborne
equipment, the autoland is often standard on many new airplanes. This
modern system gives the aircrew increased capabilities by enabling them
to make safer instrument approaches and landings than those being done
without the autoland. Autoland also refers to the landing that is accomplished
with the autoland engaged. The aircrew is required to constantly monitor
this system to ensure safe operation of the aircraft.
3) General Information. Many large transport category airplanes
are equipped with autoland systems and a few helicopters are equipped
with automatic deceleration and hover systems. As technology evolves,
the trend of using autoland systems is increasing. Autoland systems
are already standard features on many new airplanes. An air carrier,
however, is not authorized to use autoland systems to touchdown in parts
135 operations unless the particular flight control guidance system
is authorized for autoland by the OpSpecs. Part
121.579 and part
135.93 prohibit the use of most APs below certain heights (50 feet
or greater) during approach and landing operations, even during VFR
weather conditions. The intent of these rules is to provide pilots with
the terrain or obstacle clearance and the reaction time necessary to
safely intervene if the AP malfunctions.
4) Pilot Intervention. This is especially critical if the AP
abruptly commands a hard-over, nose-down condition. Many APs (“single
channel” APs) used in parts
135 operations are not designed to provide the redundancy necessary
to automatically detect all failure combinations. If such failures occur,
the pilot must intervene, disconnect the AP, and recover manually. Since
an aircraft will lose altitude if a hard-over, nose-down condition occurs,
the AP must be routinely disengaged before descending below the height
above terrain specified by § 121.579 or § 135.93, as appropriate. Failure to disconnect the AP before descending
below these heights could lead to ground contact during a recovery attempt
if a malfunction occurred. Many aircraft are now equipped, however,
with an automatic flight control guidance system (AFCGS) designed to
provide the performance, redundancy, and reliability necessary to detect
all significant failure combinations and to prevent the AP from failing
in a hard-over, nose-down condition (zero height loss). With these aircraft
and equipment combinations, the safety objective of §§
135.93 can be met even if the system is used to touchdown. FP and
FO automatic landing systems provide this capability and can be approved
for use to touchdown. The operator’s approved training curriculum must
include training on autoland operations and the autoland equipment must
be properly certificated and maintained. Principal operations inspectors
(POI) shall authorize the use of autoland to touchdown by issuing OpSpec
C061 in accordance with § 121.579(c) or §
B. Manually Flown Flight Control Guidance Systems Certificated
for Landing Operations (HUD). Historically, pilots have not had
FD systems and other instrument information that enabled safe manual
control of an aircraft to touchdown in instrument conditions. The development
of flight control guidance systems such as HUD provides the pilot with
instrument information in a manner that enables safe manual control
of the aircraft through touchdown and rollout. The flight guidance provided
by these systems enables a pilot to duplicate the performance and functions
of an autoland system. These systems provide flight guidance information
equivalent to the performance, redundancy, reliability, and the hard-over,
nose-down protection provided by autoland systems, which are approved
for use to touchdown. Manually flown flight control guidance systems
certified for landing operations can be approved for use to touchdown.
The operator’s approved training curriculums must include training on
such manually flown operations, and the equipment must be properly certificated
and maintained. Use of these manually flown systems to touchdown can
be authorized by the issuance of OpSpec C062 in accordance with this
4-157 CONCEPT OF CIRCLING MANEUVERS.
A. Instrument Approach Design Criteria. In many situations,
instrument approach design criteria will not permit a straight-in approach
to the landing runway. In these situations, a circling procedure is
necessary to maneuver the aircraft to a landing on the intended runway.
Circling maneuvers are usually necessary when there is an obstacle or
terrain problem. Circling maneuvers are also required when a NAVAID
is located in a position that precludes a straight‑in approach to the
intended landing runway. U.S. criteria require a circling maneuver if
the inbound course is offset more than 30 degrees from the RCL. Unless
specifically restricted in the procedure, a circling maneuver can be
initiated from any IAP and must be conducted entirely by external visual
references. Electronic course or glidepath guidance cannot be used to
perform a circling maneuver.
B. The Circling Maneuver. A circling maneuver is not
an instrument maneuver. Sufficient visual references for manually maneuvering
the aircraft to a landing must be maintained throughout a circling maneuver.
The pilot must keep the aircraft’s position within the established maneuvering
area while performing the circling maneuver. The circling MDA must be
maintained until an aircraft (using normal maneuvers) is in a position
from which a normal descent (less than 1,000 feet per minute) can be
made to touchdown (decelerate to air taxi or hover for helicopters)
within the TDZ. It is critical for pilots to understand that the published
missed approach procedure may not provide adequate obstacle clearance,
especially during the initial portion of a missed approach executed
during a circling maneuver. The published missed approach is designed
to provide obstacle clearance only when the missed approach is executed
on the published final approach course at or above the MDA, and before
passing the MAP. A published missed approach may not guarantee the necessary
safety margin when a missed approach is executed past the MAP and/or
below the MDA. The aircraft must remain within the established circling
maneuvering area until the aircraft is at or above the MDA and established
on the missed approach course. The following statements summarize the
basic concepts of a circling maneuver:
· A circling maneuver is a visual maneuver.
· Sufficient visual references to manually maneuver the
aircraft to a landing must be maintained throughout a circling maneuver.
· The aircraft must be maintained at the MDA until it is
at a position from which a safe landing can be made.
· A missed approach must be executed when external visual
references are lost or sufficient visual cues to manually maneuver the
aircraft cannot be maintained.
C. Missed Approach Procedure. The traditional published
missed approach procedure does not guarantee obstacle clearance during
the initial phases of a missed approach if initiated during a circling
maneuver after descending below MDA or after MAP. When a pilot loses
visual reference while circling to land, follow the missed approach
specified for the approach procedure. An initial climbing turn toward
the landing runway will ensure that the aircraft remains within the
circling obstruction clearance area. Continue to turn until established
on the missed approach course. An immediate climb must be initiated
because obstacle clearance is not guaranteed beyond the MAP.
4-158 LOOK-SEE APPROACHES. A look-see approach is not an
actual type of approach, such as ILS or RNAV (GPS). Rather, it is a
term used to describe the operation of commencing and continuing an
instrument approach to DA/DH or MDA to determine if the seeing‑conditions
actually available at those points are sufficient to continue to a landing.
Look-see approaches are approaches that can be started and then continued
to the DA/DH or the MDA and the MAP, even when the weather conditions
are reported to be below the authorized IFR landing minimums. This operation
applies domestically only to part
91 operators. This operation may be conducted in certain foreign
countries by part
121 operators. Upon arrival at the MDA and before passing the MAP,
or upon arrival at the DA/DH, the approach may be continued below DA/DH
or MDA if the seeing‑conditions required by §
121.651(c) or part
91, §§ 91.175(c) and
91.175(1) are met. A pilot can continue to land using external visual
reference if the necessary seeing‑conditions are established before
passing DA/DH or MDA/MAP. The operational need for look-see approaches
is created by wide variations among foreign countries in weather observing,
weather reporting practices, and because of limitations associated with
manually derived and forwarded weather reports (especially during rapidly
changing weather conditions). The weather observation is often taken
from a location that is several miles from the landing surface, and
may not be representative of seeing‑conditions encountered at DA/DH,
MDA/MAP, or during landing. Part
121 operators may conduct look-see approaches at foreign airports
(civil and military) unless the foreign country specifically prohibits
121 operators, however, are prohibited from conducting look-see
approaches at all U.S. airports including U.S. domestic, U.S. territorial,
and U.S. military airports (including U.S. military airports in foreign
135 operators are prohibited from conducting look-see approaches
at all airports, both domestic and foreign, by § 135.225.
4-159 CONCEPTS OF DA/DH.
A. DA/DH Concept. The DA/DH concept is the foundation
for CAT I and CAT II approach and landing operations. It is also an
essential concept in certain CAT III operations. This concept evolved
after the introduction of turbojets in 1958. It was established to resolve
problems created by the use of a ceiling as an element of operating
minimums, especially during rapidly changing weather conditions. The
use of the DA/DH concept also enhances safety of operations in degraded
seeing‑conditions. A DA/DH is established to require that the pilot,
at the specified height, decide whether adequate visual references are
available for accomplishing the following actions:
· Verifying that the aircraft is in a position that will permit
a safe landing in the TDZ.
· Determining that sufficient external visual references
are available to manually maneuver the aircraft (or assess AP maneuvering
in CAT II and CAT III operations) into alignment with the RCL.
· Determining that the aircraft can be maneuvered to touchdown
within the TDZ, that directional control can be maintained on the runway,
and that the aircraft can be stopped within the available runway length.
· For helicopter operations, determining that sufficient
visual references are available to maneuver the helicopter to align
with the landing area; to decelerate to air taxi or to hover; and to
maintain directional control while air taxiing.
B. Operational Viewpoint. From an operational viewpoint,
DA/DH is the limit to which a pilot can descend before having to decide
to continue the approach by visual means. If the visual references required
to safely continue the approach have not been established before passing
DA/DH, a missed approach must be executed at DA/DH. This does not mean
that a pilot waits until arriving at DA/DH before deciding to go around
or to continue the approach based on visual references.
1) The decisionmaking process begins when the approach is initiated
and continues throughout the approach. A pilot must continually evaluate
course and glidepath displacement information throughout the approach.
Knowing that significant changes cannot occur instantaneously, a pilot
begins to formulate a decision concerning the probable success of the
approach long before reaching DA/DH.
2) Although DA/DH is a specified point in space (PinS) at which
a pilot must make an operational decision, the pilot accumulates the
information required to make that decision throughout the approach.
It is incorrect to assume that all aspects of the decisionmaking process
are delayed until the critical instant the aircraft arrives at DA/DH.
The visual cues, which become available during the descent to DA/DH,
enhance the pilot’s formulation of the decision, which must be made
3) The operational decision to continue the approach by visual
means, however, must be made before passing DA/DH. At DA/DH, a decision
to continue the approach by reference to visual cues is appropriate
if a pilot is satisfied that the total pattern of the visual cues provides
sufficient guidance and that the aircraft is in a position and tracking
so as to remain within a position from which a safe landing can be made.
However, if a pilot is not satisfied that all of these conditions exist,
a missed approach must be executed.
C. Before Passing DA/DH. The decision that the pilot
must make before passing DA/DH is not a commitment to land. It is a
decision to continue the approach based on visual cues. This distinction
is important since the possibility exists that, after passing DA/DH,
visual cues may become inadequate to safely complete the landing, or
the aircraft may deviate from the flightpath to a point where a safe
landing cannot be assured. Since many variables are involved, the final
decision to commit to a landing is the PIC’s and is primarily a judgment
based on all the relevant operational factors. The PIC shall usually
delay the decision to commit to a landing until the final stages of
flare and landing.
1) The following is a list of statements that describe what DA/DH
· DA/DH is a specified decision point.
· DA/DH is the point at which a specific action must be
initiated (either continue the approach by reference to visual aids
· DA/DH is the limit to which a pilot can descend before
having to decide to continue the approach using external visual references.
2) The following is a list of statements that describe what
DA/DH is not.
· DA/DH is not a point where the decisionmaking process
· DA/DH is not the latest point at which a go-around could
or should be made.
· DA/DH is not a point where all aspects of the decision
are instantaneously formulated.
D. Vertical Navigation (VNAV) Approach Procedures Using DA/DH—OpSpec
C073. Based on near-term safety benefits of using a continuously
defined Vertical Path (VPATH) to the runway, and a long-term goal of
simplifying approach training and qualification standards, users have
indicated their intent to begin additional use of VNAV capability for
instrument approaches. The applicable procedures, operating criteria,
and revisions to the operator’s OpSpecs, if applicable, to permit additional
use of VNAV capability of FMS for IAPs are contained in
Volume 3, Chapter 18, Section 5.
4-160 CONCEPT OF MDA AND MAP. The MDA/MAP concept is the
foundation for safe CAT I approach operations that do not have VPATH
guidance (e.g., VOR or lateral navigation (LNAV)). Electronic glidepath
information cannot be provided at certain locations because of obstacle
or terrain problems, NAVAID sighting problems, and cost benefit factors.
The MDA/MAP concept provides for safe approach operations in instrument
conditions at locations that do not have VPATH guidance.
A. MDA. An MDA is the lowest permissible height (for
a Nonprecision Approach (NPA) procedure) at which an aircraft can be
controlled by reference only to instrument information. After passing
the final approach fix (FAF), a pilot should descend on a VPATH that
will enable a stabilized approach and, if the visual conditions are
adequate, a descent to the runway without any intermediate level-off
at the MDA. If the visual conditions are not adequate, the pilot must
level off at the MDA until sufficient visual references are available
to safely complete the approach and landing. For unusual approach procedures
and environmental conditions (offset final course, crosswinds, icing,
etc.) a pilot may descend to the MDA at an expedited rate (not to exceed
1000 feet per minute).
B. Establish an MDA. An MDA is established to require that
the pilot, before descending below the specified height and before passing
the MAP, determines that adequate visual references are available for
accomplishing the following actions:
· Verifying that the aircraft is in a position that will
permit a safe landing in the TDZ.
· Determining that sufficient visual references are available
to manually maneuver the aircraft to align it with the RCL, touchdown
within the TDZ, and maintain directional control on the runway.
· For helicopter operations, determining that sufficient
visual references are available to maneuver the helicopter to align
with the landing area, decelerate to air taxi or hover, and maintain
directional control while air taxiing.
1) The following is a list of statements that describe what
· MDA is the lowest permissible height at which an approach
can be continued by reference solely to flight instruments.
· MDA is the limit to which a pilot can descend before having
to decide whether or not to continue the approach by using external
· MDA is the minimum height above the surface to which the
aircraft can descend, unless the pilot determines that the aircraft
is in a position from which it can be safely maneuvered using normal
rates of descent (less than 1,000 feet per minute) to a touchdown within
the TDZ (decelerate to air taxi or hover for helicopters).
2) The following is a list of statements that describe what
MDA is not.
· MDA is not a specified decision point.
· MDA is not a point at which a specific action is initiated.
· MDA is not a point where the decision process begins.
· MDA is not the latest point at which a go-around could
or should be made.
· MDA is not a point where all aspects of the decision are
C. MAP. For an approach that does not have vertical guidance,
it is necessary to define a point on or near the airport where a missed
approach must be executed, if adequate external visual references for
safely continuing the approach are not available. This point is specified
as the MAP. A MAP is a three-dimensional airborne position where the
MDA passes over a specified geographic fix.
1) The following is a list of statements which describe what
· MAP is a specified decision point.
· MAP is the last point at which the approach can be continued
by reference solely to flight instruments. After the MAP, the instrument
approach must be discontinued.
· MAP is the last point at which the published missed approach
can be safely executed in instrument conditions.
2) The following is a list of statements which describe what
MAP is not.
· MAP is not always the last point at which a pilot can
decide to continue the approach by external visual references. Often,
the MAP is located at a point where a pilot cannot safely descend and
land if the MDA is maintained until arriving at the MAP (for example,
when the MAP is located over the VOR on the airport).
· MAP is not a point where a decision or commitment to land
· MAP is not a point where the decision process begins.
· MAP is not a point where all aspects of the decision are
4-161 MINIMUM INSTRUMENT FLIGHT ALTITUDES. Except for certain
CAT III operations, all instrument approach and landing operations have
limitations related to obstacles, airborne instrumentation and equipment,
ground-based navigation equipment, and/or visual aids. Because of these
limitations, external visual information is required to safely complete
instrument approaches and landings. Airborne instruments and equipment
and the signals in space radiated by ground-based NAVAIDs must provide
pilots adequate guidance to safely control an aircraft by reference
solely to instruments until the aircraft arrives at a preestablished
minimum height or altitude (DA/DH or MDA) for instrument flight. The
total system (airborne and ground-based) does not provide this capability
below the minimum height or altitude for instrument flight. Therefore,
descent below the specified minimum height or altitude for instrument
flight can only be safely accomplished when adequate external visual
references are available. If adequate external visual references are
not established, a pilot must execute an instrument missed approach
at or before passing a preestablished MAP.
NOTE: Descent below the specified minimum IFR altitude without
adequate visual references to control and maneuver the aircraft to a
landing is unsafe and prohibited. The minimum height or altitude for
instrument flight for an instrument approach and landing is specified
in various ways depending on the type and category of the instrument
A. NPA Procedures. The minimum heights or altitudes for
IAPs that do not have vertical guidance can be specified as an MDA,
height above touchdown (HAT), height above airport (HAA), minimum descent
height (MDH), Obstacle Clearance Altitude (OCA), Obstacle Clearance
Height (OCH), or Obstacle Clearance Limit (OCL). MDA, HAT, HATh, and
HAA are used by the United States and certain foreign countries that
use TERPS criteria. OCA, OCH, and OCL are used in most foreign countries
and are established in accordance with ICAO PANS-OPS. Although the current
edition of ICAO PANS-OPS eliminated use of OCL, some countries still
use OCL criteria from previous editions of PANS-OPS. Some countries,
in addition to OCA and OCH, provide MDA and MDH. MDA and OCA are barometric
flight altitudes referenced to mean sea level (MSL). HAT, HATh, HAA,
MDH, OCH, and OCL are radio or radar altitudes referenced to either
the elevation of the airport, the elevation of the TDZ, or the elevation
of the landing threshold.
· MDA or OCA may be specified for any approach procedure that does
not have vertical guidance.
· HAT, MDH, OCH, or OCL may be specified for straight-in
approach procedures that do not have vertical guidance.
· HAA, MDH, OCH, or OCL may be specified for circling maneuvers.
B. Precision and Approach Procedures with Vertical Guidance
(APV) Approach Procedures. The minimum heights or altitudes for
IAP with vertical guidance can be specified as a decision altitude (DA),
OCA, DH, OCH, or OCL. In the United States and certain foreign countries
that use U.S. TERPS criteria, the minimum instrument flight altitude
for precision with vertical guidance and APV is DA/DH. DA/DH is specified
as a DA referenced to MSL for aircraft equipped with only barometric
altimeters and as HAT or HATh (for procedures developed with harmonized
visibility minimums) for aircraft equipped with radio altimeter or RAs.
DA, DH, OCH, and OCL are used in most foreign countries and are established
in accordance with various versions of ICAO PANS-OPS. DA and OCA are
referenced to a barometric altitude (MSL). DH (in most countries), OCH,
and OCL are referenced to a radio or radar height above either the elevation
of the airport, the elevation of the TDZ, or the elevation of the landing
C. Lowest Permissible Height or Altitude for Instrument Flight.
The lowest permissible height or altitude for instrument flight for
any approach cannot be lower than any of the following:
· Minimum height specified by the FAA-approved Aircraft
Flight Manual (AFM).
· Minimum height or altitude for which the signals from
ground-based or space-based navigation equipment can be relied upon
for instrument flight.
· Minimum height or altitude that provides adequate obstacle
· Minimum height or altitude authorized for the flightcrew.
· Minimum height or altitude authorized for the operator
for that aircraft and equipment combination.
· Minimum height or altitude permitted by the operative
airborne and ground-based or space-based equipment.
· Minimum height or altitude published or otherwise established
for the instrument approach.
· Minimum height or altitude authorized in OpSpecs for the
operation being conducted.
4-162 OPERATING MINIMUMS. The lowest operating minimums
for operations conducted under 14 CFR parts 91K,
135 are specified in standard OpSpecs, MSpecs, and LOAs as appropriate.
In general, an air carrier is authorized to use operating minimums specified
by the following groups of IAP, provided the minimums are not lower
than the lowest minimums specified in the air carrier’s OpSpec for any
particular type of approach procedure.
· U.S. military IAPs at U.S. military airports.
· Any IAPs approved and incorporated into the OpSpecs.
· ICAO contracting State IAPs at foreign airports.
· IAPs established by an air carrier at foreign airports,
provided the procedure is accepted in accordance with the OpSpecs.
A. Straight-In Minimums for Approaches with a DA/DH.
The lowest permissible DA/DH and visibility minimums for all airplanes
conducting standard straight-in IAPs other than CAT II or CAT III that
have a DA/DH are HAT 200 and RVR 1800. The lowest permissible DA/DH
and visibility minimums for helicopters is ¼ statute mile visibility
or RVR 1200. These basic DA/DH and visibility minimums are normally
restricted to runways that are equipped with a lighting system consisting
of TDZ and RCL lights and medium intensity approach lighting system
with runway alignment indicator lights (MALSR), simplified short approach
lighting system with runway alignment indicator lights (SSALR), and
ALSF-1 or ALSF-2 approach lighting systems. RVR 1800 is authorized when
FD, AP, or HUD is used in lieu of TDZ and RCL lights. Additionally,
SA CAT I operations are discussed in
Volume 4, Chapter 2, Section 6.
B. Straight-In Minimums for Approaches with an MDA. The
lowest permissible MDA and visibility minimums for Categories A, B,
C, and D aircraft during the conduct of straight-in IAPs that have an
MDA are HAT 250 and ½ statute mile visibility or RVR 2400. The lowest
permissible MDA and visibility minimums for helicopters operated at
90 knots or less are HAT 250 and ¼ statute mile visibility or RVR 1600.
The lowest MDA and visibility minimums for helicopters operated at more
than 90 knots are HAT 250 and ½ statute mile visibility or RVR 2400.
These minimums are the lowest authorized for approaches that have an
MDA and are restricted to runways that are equipped with MALSR, SSALR,
ALSF-1, or ALSF-2 approach lighting systems, or foreign equivalents.
C. Controlling Minimum Concept. The concept of a controlling
minimum is based on reported weather conditions at the destination airport.
The controlling minimum concept includes considerations for the reported
weather conditions, the capabilities of the flightcrew, and the capabilities
of the airborne and ground- or space-based equipment. This concept prohibits
a pilot from continuing past the FAF or beginning the FAS of an IAP
unless the reported visibility (RVV or RVR, if applicable) is equal
to or greater than the authorized visibility (RVV or RVR) minimum for
1) Objective. The basic objective of the controlling minimum
concept is to provide reasonable assurance that once the aircraft begins
the FAS, the pilot will be able to safely complete the landing. The
controlling minimum concept, however, permits a pilot to continue a
CAT I approach to DA/DH if the visibility/RVV/RVR was reported to be
at or above the controlling minimum when the pilot began the FAS, even
though a later visibility/RVV/RVR report indicates a below-minimum condition.
RVR reports, when available for a particular runway, are the reports
(controlling reports) that must be used for controlling whether an approach
to, and landing on, that runway is authorized or prohibited.
91K Controlling Minimum. The controlling minimums concept as
described above is not applicable to part
91K operators when determining if the pilot can continue past the
FAF or begin the FAS. Parts
91K operations can begin an approach and continue to the DA/DH or
the MDA and the MAP, even when the weather conditions are reported to
be below the authorized IFR landing minimums. Upon arrival at the MDA
and before passing the MAP, or upon arrival at the DA/DH, the approach may be continued
below DA/DH or MDA to the runway if the seeing‑conditions required by
91.175(c)(d) or §
91.175(1) are met.
121 Controlling Minimum. The controlling minimum concept for
operations conducted under part
121 is implemented by §
121.651(b). For these operations, the controlling minimum must be
used at civilian airports within the United States and its territories,
and at U.S. military airports, unless the provisions of §
121.651(d) are met. Section
121.651(d) permits a pilot to begin the FAS, even though the reported
visibility/RVV/RVR is below the controlling minimum, if the approach
procedure is an ILS and the flight is actively monitored by a PAR.
a) Therefore, pilots are not constrained by the controlling minimum
on runways with ILS and active PAR facilities, provided the provisions
121.651(d) are met. The controlling minimum concept allows for a
pilot to continue a CAT I approach to DA/DH or MDA if the visibility/RVV/RVR
was reported to be at or above the controlling minimum when the pilot
began the FAS, even though a later visibility RVV/RVR report indicates
a below-minimum condition.
b) Upon reaching DA/DH or MDA and before passing the MAP, the approach
may be continued below DA/DH or MDA to touchdown if the requirements
121.651(c) are met, even though the visibility/RVV/RVR is reported
to be below the controlling minimum. The controlling minimum concept
does not apply to part
121 operations conducted at civilian airports in many foreign countries.
In foreign countries, part
121 operators may conduct look-see approaches unless the rules of
a foreign country (such as the United Kingdom) prohibit look-see approaches.
If the rules of the foreign country prohibit look-see approaches, the
controlling minimum concept applies in that country.
135 Controlling Minimum. The controlling minimum concept for
135 differs in application from part
91 applies to all parts
135 operations whether they are conducted in foreign countries or
the United States (see §§
135.3(b)). Operations conducted under parts
135 must also be in compliance with §§
135.225 (which applies to all operations within the United States,
its territories, U.S. military airports, and foreign airports). For
135 operations, the controlling minimum concept must be used at
all airports (with the exception of a part
135 “eligible on-demand” operator who is permitted to start an approach
without weather reported above landing minimums (see §135.225(b)).
a) As a consequence, §§
135.225(b) prohibit parts
135 operators from conducting look-see approaches at any airport.
The controlling minimum concept, however, allows for a pilot to continue
a CAT I approach to DA/DH or MDA if the visibility/RVV/RVR was reported
to be at or above the controlling minimum when the pilot began the FAS,
even though a later visibility/RVV/RVR report indicates a below-minimum
b) The controlling minimum concept also allows for a pilot (upon
reaching DA/DH or MDA and before passing the MAP) to continue the approach
below DA/DH or MDA and to touchdown, if the requirements of § 91.175 are met, even though the visibility/RVR is reported to be
below the controlling minimum.
4-163 MAXIMUM SINK RATES.
A. Perceptual Limitations. Restricted seeing‑conditions significantly
affect a pilot’s ability to visually detect or perceive vertical height,
sink rate (vertical velocity), and vertical acceleration. As seeing‑conditions
decrease, the pilot’s ability to perceive vertical height, sink rate,
and vertical acceleration degrades faster than the ability to perceive
lateral errors and lateral accelerations. Personnel establishing operating
minimums must consider these human perceptual limitations.
B. Aircraft Structural Limitations. According to structural
design criteria, the aircraft structure must tolerate touchdown sink
rates (vertical velocity) of at least 10 feet per second (600 feet per
minute). Touchdown sink rates higher than the maximum rates evaluated
during the certification of an aircraft can cause serious structural
damage, including catastrophic failure. Therefore, instrument procedure
design must provide for sink rates that give a pilot the capability
of detecting unacceptable situations and adjusting the flightpath to
achieve a safe landing, considering available visual aids and operating
minimums. Visual aids and operating minimums must provide a high probability
that a pilot will be able to control the aircraft adequately and adjust
the vertical flightpath to achieve acceptable sink rates at touchdown
and touchdown within the TDZ.
C. Maximum Acceptable Sink Rates. Operational experience
and research have shown that a sink rate of greater than approximately
1,000 feet per minute (16.67 feet per second) is unacceptable during
the final stages of an approach (below 1,000 feet above ground level
(AGL)). This is due to a human perceptual limitation that is independent
of the type of airplane operated and is equally applicable to helicopters.
Therefore, the IAPs and the operational practices and techniques must
ensure that sink rates greater than 1,000 feet per minute are not required
or permitted in either the instrument or visual portions of an approach
and landing operation. Operating minimums and available visual aids
must provide reasonable assurance that a pilot will have adequate external
visual references in the visual portions of all IFP (certain CAT III
operations excepted). To be considered adequate, these external visual
references must permit a pilot to adequately perceive sink rates and
manually maneuver the aircraft (or evaluate AP performance) to achieve
an acceptable touchdown sink rate and touchdown point, considering the
operating minimums and the available visual aids.
4-164 EFFECTS OF AIRCRAFT/COCKPIT DESIGN ON seeing‑conditions.
A. Design of an Aircraft. The overall design of an aircraft
and the design of a cockpit significantly affect seeing‑conditions during
the latter stage of an approach and landing and during the initial stage
of a takeoff. Cockpit design has a direct affect on a pilot’s ability
to determine the three-dimensional position of an aircraft in relation
to a landing or takeoff surface and, consequently, on the ability to
safely control the flightpath of the aircraft. Therefore, cockpit design
is a significant factor in establishing operating minimums of a particular
aircraft. Generally, aircraft with larger cockpit cutoff angles (better
downward viewing angles over the nose) and shallower landing pitch attitudes
provide for better seeing‑conditions. Improved seeing‑conditions derived
from improved cockpit design can be used to justify lower operating
minimums. seeing‑conditions are affected by geometric factors related
to the design of an aircraft’s structure and by aerodynamic factors
related to an aircraft’s pitch axis. When considering aircraft/cockpit
design, it is important to note the following:
· The radio (radar) altimeter is calibrated to read the height
of the landing gear above the terrain (when in the landing configuration).
· The glidepath antenna tracks down the centerline of the
glideslope when the instruments in the cockpit indicate the aircraft
is on glidepath.
· The pilot’s eyes are always higher than what is indicated
on the radio (radar) altimeter.
· The pilot’s eyes are above the electronic glideslope in
B. Aircraft and Cockpit Physical Design. The significant
factors related to the physical design of an aircraft and cockpit combination
that affect seeing‑conditions most are as follows:
· Distance along the longitudinal axis from directly above
the main landing gear to directly beneath the pilot’s eyes.
· Vertical distance from the pilot’s eyes to a position
abeam the main landing gear.
· Distance along the longitudinal axis from directly beneath
the glideslope antenna to directly beneath the pilot’s eyes.
· Vertical distance from the glideslope antenna to abeam
the pilot’s eyes.
· Cockpit cutoff (CCO) angle.
C. The CCO Angle. The CCO angle is the angle, measured
downward, from the longitudinal axis of the aircraft (zero pitch reference)
to the lowest (most depressed) angle that can be seen over the aircraft’s
nose from the proper sitting position (eye reference position). The
CCO angle in most transport category aircraft is between 15 and 25 degrees.
Although many VFR helicopters have an excellent CCO angle, most IFR
helicopters have CCO angles equivalent to transport category aircraft.
D. Aircraft Aerodynamic Design. The significant factors
associated with the aerodynamic design of an aircraft that affect seeing‑conditions
are related to pitch attitudes. The pitch attitudes necessary for final
approach, flare (deceleration for rotorcraft), and landing (air taxiing
for rotorcraft) have a major affect on seeing‑conditions. This is because
a nose-up attitude reduces the downward viewing angle relative to the
horizon, which reduces seeing‑conditions.
1) For example, an aircraft with an excellent CCO angle of 21
degrees and a high final approach pitch attitude of 8 degrees would
have a seeing condition comparable to a similar size aircraft having
a poor CCO angle of 13 degrees and a 0 degree pitch attitude. Since
the pitch attitude on final approach varies with approach speed, aircraft
configuration, and gross weight, the seeing‑conditions change as these
operational factors change.
2) The aircraft’s flare characteristics (deceleration for rotorcraft)
can also have a significant effect on the seeing‑conditions during landing.
The seeing‑conditions during flare decrease if any positive pitch change
is required. In helicopters, the most severe degradation to the seeing‑conditions
occurs during deceleration to air taxi or hover. Often, the deceleration
rate in a helicopter must be limited to maintain adequate seeing‑conditions.
3) For example, when a typical IFR helicopter with an 18 degree
CCO angle and a 0 degree final approach attitude approaches an 18 degree
pitch attitude during a maximum effort deceleration, the pilot will lose sight of the landing surface.
At an 18 degree pitch attitude with an 18 degree CCO angle, the lowest
downward viewing angle would be parallel with the horizon.
4) Therefore, a deceleration pitch attitude must be maintained
significantly below 18 degrees to maintain adequate visual references
with the landing surface. A similar situation is encountered in turbojet
airplanes during takeoff rotation and initial climb when external visual
references can be lost.
E. Eye Reference Position. Eye reference position is
a critical factor in achieving optimum seeing‑conditions. A pilot’s
seat must be individually adjusted so that the pilot’s eyes are located
at an optimum eye reference position. When seated in this position,
a pilot should be able to take advantage of the full CCO angle, maintain
reference with the necessary flight instruments, and operate all necessary
controls. Many aircraft have special devices that indicate proper seat
adjustment. Improper seat adjustment, especially in CAT II and III operations,
can prevent the pilot from acquiring adequate external visual reference
upon arrival at DA/DH or MDA/MAP.
1) The seating position commonly used for en route operations
in many aircraft is too low and too far aft for the pilot to achieve
optimum seeing‑conditions during approach and landing operations. This
lower and further aft seating position results in a reduction of the
CCO angle, which degrades the seeing‑conditions by reducing the segment
of the approach and landing surface visible over the aircraft’s nose.
2) A pilot maintaining this undesirable seating position during
approach and landing may tend to compensate for the reduced CCO angle,
and its effects, by leaning forward in an attempt to acquire the necessary
external visual references. A consequence of this practice is a tendency
to unintentionally reduce the pitch attitude. Since seeing‑conditions
improve as the nose is lowered, this tendency to reduce pitch attitude
can contribute to the tendency to duck under, which has resulted in
landings short of the runway.
4-165 SAFETY DURING MISSED APPROACHES AND GO-AROUNDS.
A. Executing a Go-Around. Most aircraft used in air transportation
have the capability, in a normal approach and landing configuration,
of safely executing a go-around from any point before touchdown, even
when significant failures occur, such as engine, hydraulic, or AP failures.
This aircraft performance capability for safety in go‑arounds should
be provided for, particularly for go-arounds caused by operational factors,
such as airborne and ground-based equipment failures, ATC contingencies,
loss of external visual references, and misalignment with the landing
surface. This capability is required in all CAT II and CAT III operations.
When establishing operating minimums for aircraft that do not have this
capability, the consequences of the failures that would preclude a safe
go-around must be considered. Operating minimums for aircraft without
the performance capability to safely go around following engine failure
must provide adequate seeing‑conditions to successfully accomplish a
forced landing in a preestablished location. The following factors must
be considered when evaluating the safety of go-arounds from any point
in the approach before touchdown:
B. Go-Around Capability. The go-around capability is based
on normal operating conditions at the lowest authorized operating minimum.
Factors related to geometric limitations of the aircraft during the
transition to a go-around (such as tail strike, or rotor strike) must
be considered. Other factors such as the available visual cues, AP or
FD mode switching, altitude loss in transition to go-around, and altitude
loss due to AP malfunction must also be considered.
C. Inadvertent Touchdown. If a go-around could result
in an inadvertent touchdown, the safety of such an event must be considered.
The aircraft design and/or procedures used must accommodate for relevant
factors. Examples of relevant factors that must be considered include
operation of engines, the operation of autothrottle, autobrakes, autospoilers,
AP mode switching, and other systems that could be adversely affected
by an inadvertent touchdown.
D. Failure Condition in the Aircraft. If the occurrence
of any failure condition in the aircraft or its associated equipment
could preclude a safe go-around from low altitude, then these failure
conditions must be clearly identified. In these cases, a minimum height
must be specified from which a safe go-around can be initiated if the
failure occurs. If the failure occurs below the specified height, pilots
must be made aware of the effects or consequences of any attempt to
E. Appropriate Procedures for Low-Altitude Go-Arounds.
Information must be provided to the flightcrew concerning appropriate
procedures for low altitude go-arounds and the height loss expected.
If the conduct of certain approach and landing operations is authorized
with an engine-out, height loss information for engine-out operations
must also be provided to the flightcrew.
4-166 FUNCTION OF EXTERNAL VISUAL REFERENCES. Except for
certain CAT III operations, external visual information is essential
for a pilot to safely take off or to complete an instrument approach
and landing. This external visual information (visual cues) is necessary
for a pilot when assessing the three-dimensional position of the aircraft,
its velocity, and its acceleration or deceleration in relation to the
intended landing or takeoff surface. This information is essential for
a pilot when manually maneuvering (or when evaluating the AP’s performance
in maneuvering) the aircraft into alignment with the centerline of a
landing or takeoff surface. External visual references are essential
for a pilot to safely touchdown (decelerate to air taxi/hover for rotorcraft)
within the TDZ and for maintaining directional control to stop on the
runway (maintain directional control and avoid obstacles while air taxiing
for rotorcraft). In degraded seeing‑conditions, the quality of external
visual information can be significantly improved by use of visual aids,
such as runway markings and lighting. Such visual aids are necessary
to increase the conspicuousness of the landing or takeoff surface. These
aids provide pilots with the necessary visual references during takeoff,
the final stages of approach and landing, and ground movement. The importance
of visual aids increases as seeing‑conditions decrease.
A. Lateral Position and Crosstrack Velocity or Acceleration.
Approach lighting, TDZ lighting, RCL lighting, runway edge lighting,
and runway markings provide visual references to pilots for assessing
lateral position and crosstrack velocity or acceleration.
B. Visual Roll References During Landing, Takeoff, Rotation,
and Initial Climb. Approach lighting, threshold lighting, in-runway
lighting, and runway markings provide visual roll references during
landing, takeoff, rotation, and initial climb.
C. Visual Information for a Pilot. TDZ lighting and runway
markings indicate the plane of a landing surface and identify the touchdown
area, thereby providing a vertical and longitudinal reference. These
visual aids provide necessary visual information for a pilot to determine
vertical position, sink rate, and vertical acceleration or deceleration.
D. Adequate Alignment and Directional Control Information.
The visual guidance information from in‑runway lights and/or markings
must be sufficient to ensure adequate alignment and directional control
information during takeoff or during final stages of landing and deceleration.
E. External Visual Aids. Reference to external visual
aids is a primary requirement for controlling the aircraft’s flightpath
when operating below the minimum altitude (height) published for instrument
4-167 MINIMUM VISIBILITY, RVV, AND/OR RVR. Upon arrival
at the minimum height or altitude for instrument flight and before passing
a preestablished decision point, a pilot must establish adequate seeing‑conditions
to safely complete the approach and landing.
A. Establishing Operating Minimums. Operating minimums
are expressed as visibility, RVV or RVR. Criteria for establishing operating
minimums must provide a reasonable assurance that a pilot can establish
the required seeing‑conditions before passing the decision point. This
criterion provides this assurance if the weather conditions are reported
to be at or above the landing minimum when the approach is initiated.
To achieve this objective, the operating minimums specified for the
procedure (visibility, RVV, RVR) must be compatible with the minimum
height or altitude for instrument flight and the decision point specified
for the procedure.
B. Establishing Visual Reference. Therefore, when the
reported weather conditions are at the authorized minimums, a pilot
should be able to establish external visual references upon arrival
at the minimum height or altitude (DA/DH or MDA), and before passing
the decision point (DA/DH, MAP, or visual descent point (VDP)). At this
point a pilot must be able, by external visual reference, to maneuver
to a landing without exceeding a descent rate of 1,000 feet per minute
or exceeding aircraft limitations on touchdown. For example, it would
not be practical to specify a DA/DH of 200 feet (HAT 200) with an operating
minimum of RVR 700 since the first visual contact in a typical aircraft
would not occur until approximately 130 feet above the elevation of
C. Adequate External Visual References. The specified
operating minimum must also permit adequate external visual references
to be established early enough for a normal descent to landing (less
than 1,000 feet per minute). For example, it would not be reasonable
to specify an MDA equivalent to a HAT of 400 feet and an operating minimum
of RVR 1600 for typical turbojet airplanes. In this situation, the pilot
would not establish first visual contact until the airplane is within
4,000 feet of the landing threshold and would require a descent rate
much higher than 1,000 feet per minute to land within the TDZ.
4-168 CONCEPT OF RVR.
A. Operating Minimums. Operating minimums are specified in
terms of ground visibility, tower visibility, and RVR. The RVR concept
has evolved over a long period, and its use in the United States began
in 1955. As operating minimums were reduced due to improvements in airborne
and ground-based equipment, it became more likely that pilots would
not see the full length of the runway upon arrival at the specified
decision point. Positions established for taking visibility observations
were often several miles from the approach end of many runways. This
resulted in reported visibility values that frequently did not represent
the seeing‑conditions encountered during the final stages of approach
and landing. This deficiency was particularly critical when rapidly
changing weather conditions within the terminal area occurred. These
factors generated a need for systems such as RVR, which could rapidly
and reliably provide reports of the seeing‑conditions that a pilot could
expect to encounter in the TDZ and along the runway.
B. RVR Measurements. RVR measurements are taken by a
system of calibrated transmissometers and account for the effects of
ambient background light and the runway light intensity. Transmissometer
systems are strategically located to provide RVR measurement associated
with one or more of the three basic portions of a runway: the TDZ, the
runway midpoint (Mid), and the rollout end of the runway (rollout).
C. Instrumentally Derived Value. RVR is an instrumentally
derived value that reflects an artificially created seeing-condition
on or near the portion of the runway associated with the RVR report.
This artificially created seeing‑condition is achieved by using HIRLs,
as well as TDZ and RCL lights if they are installed. These lights increase
the conspicuousness of the landing surface and reach out to the pilot,
thereby creating a seeing-condition that is significantly better than
the reported ground visibility or tower visibility. Since RVR is based
on high intensity lights, an RVR report only has meaning when associated
with the seeing‑conditions on or near the portion of the runway where
the report was obtained (TDZ, Mid, or rollout). An RVR report has no
meaning unless a pilot is also seeing the high intensity lights on which
the report is based.
1) To properly apply operating minimums, it is important to
understand RVR. The following is a list of statements that describe
what RVR is.
· RVR is an instrumentally derived value.
· RVR is currently measured by transmissometers located
approximately 400 feet from RCL.
· RVR is related to the transmissivity (degree of opaqueness)
of the atmosphere.
· RVR is an approximation of the distance a pilot should
see when an aircraft is on, or slightly above, the portion of the runway
associated with the report.
· RVR is calibrated by reference to runway lights and/or
the contrast of objects.
· RVR is a value that varies with runway light setting.
· RVR is a value that only has meaning for the portions
of the runway associated with the RVR report (TDZ, Mid, or rollout).
2) The following is a list of statements that describe what
RVR is not.
· RVR is not a measure of meteorological visibility.
· RVR is not a measure of surface visibility or tower visibility.
· RVR is not a measure of seeing‑conditions on taxiways,
ramps, or aprons.
· RVR is not a measure of seeing‑conditions at or near MDA
· In the United States, RVR is not measured or reported
by a human observer.
· RVR is not “visibility.”
D. Concept of Controlling RVR. Controlling RVR means that
RVR reports are used to determine operating minimums whenever operating
minimums are specified in terms of RVR, and RVR reports are available
for the runway being used. All CAT I operating minimums below one-half
statute mile and all CAT II and III operating minimums are based on
RVR. The use of visibility is prohibited because the reported visibility
may not represent the seeing‑conditions on the runway. All takeoff minimums
below ¼ statute mile visibility (RVR 1600 for airplanes and RVR 1200
for rotorcraft) are predicated on RVR and use of visibility is prohibited.
For example, if the takeoff minimum for a particular operation is TDZ
RVR 1200/rollout RVR 1000, RVR reports are controlling and a takeoff
is prohibited unless the TDZ RVR report is at or above RVR 1200 and
the rollout RVR report is at or above RVR 1000. In this example, a takeoff
cannot be based on visibility if the RVR system is operative, even if
the reported visibility is greater than 1 statute mile.
4-169 VISUAL AIDS AND RUNWAY ENVIRONMENT.
A. Identifying Contrast Levels. A primary factor in the
identification of objects, such as landing surfaces, depends on a pilot’s
ability to see contrasts between the object and the surrounding background.
The ability to see and recognize contrasts in the brightness or color
of an object is much greater than the ability to determine the actual
level of illumination of an object. For example, a 100-watt light bulb
seems to be much brighter at night than during daylight conditions,
even though the actual level of illumination is the same.
B. Increasing Contrast Levels. The contrast between a
100-watt light and a dark night background is much greater than it is
in a daylight background. The presence of airborne particles or water
droplets causes the available light to diffuse or scatter. This scattering
effect raises the overall illumination of the background that, in turn,
reduces the level of contrast between an object and its background.
This is the primary reason why seeing‑conditions decrease when landing
into the sun on a hazy or foggy day or when the landing lights of an
aircraft are turned on in snow or fog conditions. Reduced levels of
contrast increase the difficulty of identifying objects such as snow-covered
runways or runways located in heavily lighted urban areas. As a result,
contrast levels must be increased to provide the seeing‑conditions necessary
for the safe conduct of operations with reduced operating minimums.
1) seeing‑conditions can be improved by using visual aids and
by enhancing the level of contrast within the runway environment. For
example, the difference in the level of contrast between a landing or
takeoff surface and the surrounding area can be improved through good
airport maintenance practices. Such practices as planting and maintaining
grass around a runway and between a runway and a taxiway, and plowing
snow-covered runways, improve levels of contrast. The most effective
way to improve the contrast of a landing or takeoff surface, however,
is to use visual aids because they are effective in a variety of weather
2) Visual aids such as approach lights, runway lights, and runway
markings significantly improve the contrast between a landing or takeoff
surface and the immediate surrounding area. The improved contrast provided
by approach and runway lighting significantly improves seeing‑conditions
in both night and daylight operations. Approach lighting and runway
lighting are essential elements of all landing operations conducted
in weather conditions below RVR 4000 and all takeoff operations below
4-170 THRESHOLD CROSSING HEIGHT (TCH) CONCEPT. Many complex
technical factors must be considered during the installation of ILS
and MLS equipment to support approach and landing operations at any
particular runway. The signals in space radiated by the facility must
meet required flight inspection requirements (accuracy and course structure)
for the particular category of operation to be supported. Design of
ground support systems must be such that there is an extremely small
probability of losing electronic guidance during actual operations (continuity
of service). The design must also provide for an extremely high probability
of providing continuously reliable electronic guidance (integrity).
The ILS or MLS accuracy and course structure, continuity of service,
and integrity must meet established standards for the category of operation
authorized at that facility. Another critical factor in installing and
siting these systems is the TCH. The following discussion addresses
significant factors that must be considered when establishing acceptable
A. Aircraft Glideslope/Elevation Antenna Location. The
glideslope/elevation receiver of the aircraft detects vertical movement
(displacement) of the glideslope/elevation antenna in relation to the
centerline of an electronic glideslope/elevation radiated from a ground
facility. As a result, the location of the glideslope/elevation antenna
on the aircraft directly relates to terrain and obstacle clearance during
the final stages of an approach and landing.
1) The physical dimensions and aerodynamic characteristics of
the aircraft (especially pitch attitude) are important factors in the
determination of the proper location of a glideslope reception antenna.
In conventional aircraft, the glideslope/elevation antenna is located
above the height of the main landing gear. Since an aircraft is maneuvered
so that its antenna tracks the centerline of the electronic glidepath,
the main landing gear will track below the glidepath.
2) For example, if the antenna of an aircraft is located 40
feet above the landing gear and the electronic glidepath crosses 30
feet above the runway threshold, the main landing gear will touch down
short of the runway since the antenna, not the landing gear, flies the
glidepath. This example illustrates the important relationship between
the aircraft antenna location and the electronic glidepath TCH.
3) This situation can be resolved by siting the ILS or MLS to
achieve a specified TCH and by requiring proper location of the glideslope/elevation
antenna on the aircraft. Similar problems are encountered when using
visual vertical guidance systems such as Visual Approach Slope Indicator
(VASI) or precision approach path indicator (PAPI), since the pilot’s
eyes track the visual glidepath and the gear follows a lower path. The
need to maintain certain landing gear crossing heights at the threshold
establishes the minimum safe TCH for a particular aircraft. The current
minimum TCH requirements are based on the DC-10 that has, in landing
configuration, the greatest vertical displacement between the antenna
location and the landing gear.
B. Barometric VNAV (baro-VNAV) TCHs. The most significant
factor in determining the threshold wheel crossing height for aircraft
using baro-VNAV for vertical guidance during the FAS is the vertical
distance between the static ports and the bottom of the main landing
gear, when the aircraft is in its normal approach attitude. The minimum
and maximum acceptable TCHs for these aircraft are determined in a manner
similar to ILS/MLS-equipped aircraft using the static ports and the
main landing gear height, instead of the glideslope/elevation antenna
to landing gear height.
C. Acceptable TCHs. Siting ILS or MLS equipment to achieve
a particular TCH can be a complex task. Operational experience with
citing these systems has shown a need to establish a range of acceptable
TCHs. The types of aircraft likely to use a particular facility must
be considered. Another consideration in establishing the range of acceptable
TCHs is the pilot’s ability to detect (by external visual references)
deviations from the proper glidepath and to make the necessary flightpath
adjustments for adequate landing gear clearance at the threshold. Proper
TCHs in CAT II and especially CAT III operations are more critical because
of the limited visual cues available and the use of automatic landing
D. Minimum and Maximum Acceptable TCHs in the United States.
The minimum acceptable TCH at a particular runway is determined by the
most TCH-critical aircraft likely to be used at that facility. The maximum
acceptable TCH also depends upon the types of aircraft likely to be
used at the facility. The instrument approach and landing system must
be sited so that all aircraft have a high probability of a safe touchdown
(deceleration to air taxi or hover for rotorcraft) in the TDZ. Landing
performance is based on the assumption that touchdown will occur in
the TDZ. Very high TCHs will not permit some aircraft to safely touchdown
within the TDZ, therefore maximum acceptable TCHs must also be established.
E. TCHs at Foreign Airports. Glideslope TCHs at foreign
airports may not be equivalent to U.S. criteria. It is important for
pilots and operators using foreign airports to understand the significance
of TCH and to know the minimum TCHs that can be safely used by their
aircraft. Operations should not be conducted to runways with TCHs below
minimum acceptable TCHs for any particular aircraft, unless special
limitations are placed on the conduct of the operation. These special
limitations must be such that a pilot can safely and consistently touchdown
within the TDZ and safely complete the rollout on the available runway
4-171 AIRPORT FACILITIES AND SERVICES. The varied seeing‑conditions
encountered in AWTAs require pilots to rely heavily on visual aids,
electronic guidance from ground-based facilities, and other facilities
and services provided by the airport. Therefore, basic VFR airport facilities
and services must be enhanced before safe operations can be conducted
in instrument flight conditions. Runways and taxiways must meet more
stringent criteria with respect to width, length, marking, and lighting.
Instrument approach aids and IAPs are required. Visual aids are needed
to assist a flightcrew during transition from instrument to visual flight
and during ground movement. Meteorological observation and measurement
equipment must be available to provide real-time information on weather
conditions. Equipment and procedures must be established to provide
aeronautical information on runway surface conditions and the status
of airport facilities and services.
A. VFR Airport Facilities and Services. Enhancements
to basic VFR airport facilities and services necessary to support instrument
flight operations include the following general factors:
· Physical characteristics of the runway environment, including
approach, departure, and pre-threshold terrain characteristics.
· Obstacles and the obstacle limitation assessment surfaces.
· Visual aids.
· Electronic aids.
· Secondary (standby) power supplies.
B. Physical Characteristics. Physical characteristics
of a runway environment become increasingly important as seeing‑conditions
deteriorate. Excessive runway or approach light gradients can create
undesirable visual illusions and can cause hard or long landings. Longer
runway lengths are necessary for reasons such as the tendency to land
further down the runway because of visual illusions and the increased
difficulty in controlling the aircraft’s flightpath. The topography
in the approach and pre-threshold areas should be regular and preferably
level to ensure proper operation of radio (radar) altimeters, FD systems,
and automatic landing systems.
1) The operation of automatic landing systems and other systems
that provide flight guidance during flare and landing (such as HUD)
is dependent on input from radio altimeters. As a result, the flare
profile, touchdown sink rate, and touchdown point can be adversely affected
by the profile of the pre-threshold terrain. Where the pre-threshold
terrain for a particular runway could affect safe operations (examples
include SEA 16R, CVG 36C, MSP 30L, and PIT 10L), an in-flight demonstration
must be made to determine that the flight control system of a particular
aircraft is not adversely affected by the pre-threshold terrain profile.
2) Additionally, the pre-threshold terrain at certain runways
(examples include MSP 30L and PIT 10L) may not permit a radio altimeter
to be used to define DH for CAT II or AH/DH for CAT III operations for
certain aircraft. In certain situations, an inner marker (IM) can be
used to define the CAT II DH or the CAT III AH.
C. Obstacles and Obstacle Limitation Assessment Surfaces.
Degraded seeing‑conditions decrease a pilot’s ability to see and avoid
obstacles. Therefore, it is essential that obstacle protection is provided
along the approach paths, missed approach and departure flightpaths,
and in areas on or near runways used for takeoffs and landings. Obstacle
protection criteria for different categories of operations and the various
phases of an approach, landing, missed approach, takeoff, and departure
are specified in U.S. TERPS, ICAO PANS-OPS, and applicable ACs.
1) In certain situations, obstacles may prevent the conduct
of CAT II or III operations. In other situations, a higher-than-normal
DH for CAT I or II operations may be required to guarantee obstacle
clearance upon the execution of a missed approach. During operations
using approaches with vertical guidance, it is essential to provide
obstacle protection in runway safety areas and obstacle-free zones.
A runway safety area is an area adjacent to the runway that must be
free from fixed or mobile “nonbreakable” obstructions. Runway safety
areas reduce the potential for catastrophic accidents if portions of
the aircraft structure (such as a wingtip) extend beyond the runway
edge, or if an aircraft departs the runway during a landing or takeoff
2) An obstacle-free zone is a three-dimensional area including portions
of the landing surface that provides obstacle clearance during landings
or during rejected landings, including missed approaches after touchdown.
The only fixed obstructions permitted in runway safety areas or obstacle-free
zones are frangible objects or obstructions that are fixed by their
functional purpose. “Fixed by their functional purpose” means that the
installation of the object in those areas is essential to the safe conduct
of operations on the runway; there are no alternative locations (examples
include such objects as runway lights, glideslope/elevation antennas,
and RVR reporting systems). Mobile obstructions (such as aircraft and/or
vehicles) are not permitted within runway safety areas or obstacle-free
zones while aircraft are using the runway. Aircraft, vehicles, and other
objects that could disturb ILS or MLS electronic guidance are not permitted
in ILS- or MLS-critical areas when other aircraft are critically dependent
on this type of guidance.
3) Since protection of these areas or zones is critical to safe
operations (particularly during degraded seeing‑conditions), visual
aids (such as signs, markings, or lighting) must be provided for identifying
the boundaries of these areas to pilots and operators of other vehicular
traffic. ATC procedures and ground movement restrictions must be provided
to ensure that these areas are protected.
D. Visual Aids. Visual aids are essential for most AWTAs.
Visual aids are also important for the safe and expeditious guidance
and control of taxiing aircraft. These aids include signs, markings,
and lights that identify holding points or indicate directions, and
the marking or lighting of the taxiway centerline and edges. The conspicuousness
of runway and taxiway markings deteriorates rapidly, especially at busy
airports. These markings must be frequently inspected and maintained,
particularly for CAT II or III operations.
1) All lighting systems should be monitored by ATC so that timely
information on system failures or malfunctions can be provided to pilots.
Regular visual inspections of all sections of the lighting systems are
normally used to determine the status of individual lights.
2) Therefore, it is usually only necessary for ATC to remotely
monitor lighting circuits to determine whether the proper amount of
power is being demanded by, and delivered to, the lighting systems.
Remote monitoring of approach, runway edge, and in-runway lighting is
essential during CAT II and CAT III operations, unless frequent visual
inspections (every 2 hours) or timely pilot reports indicate that the
lights are serviceable for the operations in progress.
E. Nonvisual (Electronic) Aids. Ground- or space-based
systems that provide electronic guidance must provide the quality of
guidance (flight-inspected course structure), integrity (degree of trust
that can be placed on the accuracy of the guidance), and continuity
of service (protection against loss of signal) appropriate to the category
of the operation being conducted (CAT I/CAT II/CAT II). Systems used
operations using approaches with vertical guidance must provide acceptable
flightpath angles and acceptable TCHs. A classification system has been established through ICAO for ground-based electronic systems
used for approaches with vertical guidance.
1) This classification system reflects the ground-based system
configuration, course quality, integrity, and continuity of service
capabilities. Since the electronic aids provide such a critical function,
pilots conducting takeoff or landing operations must be notified immediately
of any changes in system status or of any malfunctions or failures.
To meet this requirement, all facilities associated with ILS or MLS
ground equipment must be constantly monitored by ATC or other appropriate
2) The required levels of reliability, integrity, and continuity
of service for these facilities are usually provided by automatic electronic
monitoring systems, online standby equipment (backup transmitters),
duplication of key functions, and secondary power supplies.
F. Secondary Power Supplies. Secondary power sources
(standby power supplies) are essential for ensuring that visual aids,
electronic aids, meteorological reporting systems, and communication
facilities continue to function, even if the main source of power is
interrupted. Loss of power to these systems becomes more critical as
seeing‑conditions deteriorate. Therefore, as conditions change from
CAT I to CAT II or CAT III, the levels of required redundancy increase,
and standby power switchover times decrease. Secondary power supply
requirements are established in ICAO Annexes 10 and 14, and in various
FAA orders and ACs.
RESERVED. Paragraphs 4-172 through 4-186.