VOLUME 4 AIRCRAFT EQUIPMENT AND OPERATIONAL AUTHORIZATIONS
CHAPTER 2 ALL WEATHER OPERATIONS
Section 1 Introduction
4-146 ORGANIZATION AND OVERVIEW OF CHAPTER 2. The description of All Weather Operations (AWO) and the approval process are divided into 11 sections:
• Section 1 introduces AWO and provides an introduction, including an overview of various factors affecting
AWO, as well as a historical description of the evolution of AWO. This section contains historical and background information only. For specific authorizations and requirements, see the subsequent sections.
• Section 2 provides an overview of AWO concepts and operational requirements.
• Section 3 provides an operational approval process for other than small Category A aircraft to conduct
lower than standard Category (CAT) I operations.
• Section 4 describes the standards for the development and approval of Low Visibility Operations/Surface
Movement Guidance and Control System (LVO/SMGCS) plans for U.S. airports where scheduled air carriers are authorized to conduct operations.
• Section 5 provides an approval process for conducting CAT II operations in small Category A aircraft
under Title 14 of the Code of Federal Regulations (14 CFR) part
• Section 6 provides operational approval guidance specific to 14 CFR part
• Sections 79 are reserved.
• Section 10 provides specific approval guidance for maintenance and inspection programs
for low-visibility approach landing minima.
• Section 11 provides an introduction to performance-based operations.
4-147 GENERAL. This chapter discusses concepts, national direction, and guidance for use by Federal Aviation Administration (FAA) inspectors when evaluating,
approving, or denying requests for authorization to conduct AWO. This chapter also covers operational approvals for an operator proposing to use new aircraft, AWO operating systems, and approach
and landing operating minima. The basic premise for AWO takeoff, approach, and landing operations is that operating minima may be reduced through improvements in operational capabilities.
A. Terminology. The terminology used in this chapter is consistent with U.S. operations specifications (OpSpec), management specifications (MSpec), and Letters
of Authorization (LOA); as well as Advisory Circular (AC) 20-191, Airworthiness Approval of Airborne Systems used for Takeoff, Precision Approach, Landing, and Rollout in Low-Visibility Conditions; and AC
Criteria for Approval/Authorization of All Weather Operations (AWO) for Takeoff, Landing, and Rollout. While there are some differences between FAA and International Civil Aviation Organization (ICAO)
terminology, the broad objectives and practical operational applications are similar.
B. All Weather Operations (AWO). AWO are defined as any surface movement, takeoff, departure, approach, or landing operation in conditions where visual
reference is limited by weather. AWO in domestic and international environments are complex, with many variations in aircraft, ground equipment, procedures, and standards. FAA inspectors
must evaluate proposed AWO, giving due consideration to the following:
• Type of operation (e.g., 14 CFR part
91 subpart K (part
fixed‑wing; helicopter; or Department of Defense (DOD));
• Type of proposed AWO;
• Type of aircraft and equipage;
• Airports proposed for use;
• Operating minima proposed; and
• Operator’s experience, both in similar or other aircraft, and in the type of operation proposed.
C. Specific Standards. Specific standards are provided in this chapter and pertinent ACs to evaluate operations using aircraft and equipment that have
well-understood operational characteristics and limitations in specific AWO. When an operator requests approval to conduct operations not covered by these standards, or when an operator
requests to use lower operating minima than provided by these standards, the request must be forwarded to the Flight Technologies and Procedures Division for evaluation and development of
any additional AWO operational concepts necessary.
D. Authority and Responsibility for Approval of AWO.
1) The complex nature of AWO 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 be open, flexible, and adaptable.
2) When the safety of a proposed operation is being evaluated, subject matter experts (SME) in such areas as aircraft certification, ground equipment
design and maintenance, visual aid concepts and criteria, instrument approach procedure (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 process is particularly important in the evaluation and approval of approach and landing operations lower than standard CAT I. These
operations must be examined and approved on an operator‑by‑operator basis, and may involve various combinations of authorized minima and equipment.
4-148 EVOLUTION OF AWO. 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 AWO 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 minima
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 3½ years, turbojet operating minima for approaches with vertical guidance (called “precision approaches”)
were specified as a ceiling of 300 feet and visibility of ¾ statute mile (sm). These early minima, and the traditional ceiling and visibility criteria, were later abandoned in favor of
the decision height (DH) and visibility precision approach minima that we are familiar with today. At this point, the DH of 200 feet and a visibility of ¾ sm were adopted and became known
as the “basic turbojet minima.” Also introduced at this time was the concept of Runway Visual Range (RVR) as an alternative to prevailing visibility. These events marked the
birth of CAT I operations.
A. Evolution of CAT I Operations.
1) CAT I Operating Minima. Initial steps toward achieving current CAT I operating minima began in September 1961. These original developments became
the foundation for the building block approach, leading to further reductions in operating minima. The first air carrier CAT I operations were authorized in May 1962, utilizing the newly
reduced minima of a 200-foot ceiling and ½-sm visibility, or RVR 2600. The minima reductions were based on a combination of enhanced ground-based equipment, airborne equipment, pilot
training requirements, and operational mitigations, to include the following:
• Instrument landing systems (ILS) with a maximum glideslope (GS) angle of 3 degrees.
• High Intensity Runway Lights (HIRL).
• Full configuration approach lights with sequenced flashers.
• All-weather runway marking or runway centerline (RCL) lights.
• A flight director (FD) or automatic approach coupler (autopilot).
• An instrument failure warning system.
• One hundred hours of pilot-in-command (PIC) time in the particular type.
• Training on raw data approach to 200 feet.
• Training on FD and/or autopilot approach to 100 feet.
• Training on engine-out ILS approaches.
• Fifteen percent or 1,000 feet of additional field length (whichever is greater) over normal regulatory requirements.
• Maximum crosswind component of 10 knots.
2) Specifying the Operating Minima. The introduction of the DH and RVR concepts were finalized by the publication of U.S. Terminal Instrument Procedures
(TERPS) criteria in 1966. 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. This is especially true during rapidly changing or marginal weather conditions. While the operational use of RVR reports began in 1955, they were not available
at most major airports until the early 1960s. Beginning in 1989, all approach and landing operations using minima below ½-sm visibility have been based on RVR. However, newer technologies
(e.g., enhanced flight vision systems (EFVS)) have subsequently allowed the authorization of approach operations based on prevailing visibilities below ½ sm.
3) Reduced Operating Minima. In 1963, operating minima 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 were enabled by the requirement
for enhanced in-runway lighting systems, such as high‑intensity touchdown zone (TDZ) and RCL lighting. In 1964, the minima for runways not equipped with TDZ and RCL lights were reduced to
DH 200/RVR 2400. Improvements in visual aids have historically been critical in reducing landing minima, as they provide pilots with the seeing conditions necessary to transition to and
fly the visual segment of the approach, landing, and rollout. The requirement for improvement in the overall airborne and ground-based equipment capabilities, combined with a cautious
incremental reduction in operating minima, ensured that a high level of safety was maintained.
4) Common CAT I Operating Minima for Aircraft Categories AD. In 1988, CAT I operating minima for Category D airplanes were reduced to DH 200/RVR 1800.
This change established common CAT I minima for all airplanes based on more than 20 years of successful experience with Category B and C turbojet operations combined with research and
analysis. This research validated that the handling characteristics and seeing conditions in existing turbojet Category D airplanes were equivalent to other turbojets.
5) Other Than Standard CAT I Operating Minima. While the standard CAT I operating minima relied upon a specified level of ground-based and airborne
equipage as their basis, it was recognized that in some cases, higher levels of airborne equipage might facilitate minima at runways with lower levels of ground-based infrastructure
than would normally be required.
a) In 2005, the release of FAA Order 8400.13B, Procedures for the Approval of Special Authorization Category II and Lowest Standard Category I Operations,
first authorized the use of CAT I minima of decision altitude (DA) 200/RVR 1800 at runways without TDZ and RCL lighting, provided an FD, autopilot, or Head-Up Display (HUD) was used.
Later, this authorization was expanded to allow the same operations on runways with standard CAT I minima in cases where the TDZ and/or RCL lights were inoperative.
b) In 2009, Order 8400.13D, 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 and a visibility minimum as low as RVR 1400 at runways with reduced lighting, provided an approved
CAT II or CAT III HUD was used to DH and the aircraft and crew were operationally authorized to conduct CAT II and/or CAT III operations. In 2018, AC
the applicability of SA CAT I by introducing performance-based criteria for SA CAT I authorizations. Rather than restrict SA CAT I operations to HUD-equipped aircraft, the performance-based
criteria enable SA CAT I authorizations for various systems that similarly facilitate the pilot’s transition to the visual segment of the approach such as HUD, Synthetic Vision Guidance
System (SVGS), and autopilot to DH. Further, the publication of AC
standalone SA CAT I authorizations (i.e., SA CAT I not predicated upon CAT II or III authorization) for the first time.
6) Expansion of Common CAT I Operating Minima to Other Than ILS. Until 2017, the common CAT I operating minima were applicable only to ILS approaches.
However, based on safety analysis and operational experience, DA 200/RVR 1800 were adopted as the lowest operating minima for CAT I approaches based on Ground Based Augmentation System (GBAS)
Landing Systems (GLS), as well as for approach operations utilizing lines of minima for localizer performance with vertical guidance (LPV) on Area Navigation (RNAV) approach procedures.
B. Evolution of CAT II Operations.
1) Concepts and Criteria. The initial criteria for CAT II operations were issued in October 1964 and prompted 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.
2) Guidance During CAT II Operations. During CAT II operations, greater reliance must be placed on the guidance provided by the ground-based and airborne
systems. Therefore, design and maintenance criteria for airborne and ground-based equipment, as well as pilot training requirements, must ensure that better performance and higher reliability
are achieved by the total system. Specific requirements for ground-based equipment, airborne equipment, and pilot training may be found Order
in 8400.13, AC 20-191, and AC
3) 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 demonstrate that their selected airborne system performed, and continued to perform, at the level of precision and reliability
required. The training and qualification program 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 procedures and techniques for transitioning from instrument to visual flight at low altitude.
4) 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:
a) 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 had been attained
and maintained. This program consisted of safely accomplishing approximately 300 approaches. The operator was also required to show that the methods for failure and/or malfunction
detection and annunciation were acceptable to the Administrator.
b) 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 required to conduct a less extensive operational demonstration before receiving initial CAT II authorization.
5) 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 minima of DH 100/RVR 1200. Later,
the DH 150 restriction during the 6-month demonstration period was removed, so a typical operator today will conduct the demonstration with minima of DH 100/RVR 1600.
6) Other Than Standard CAT II Minima.
a) In 2005, Order 8400.13B provided the criteria for SA CAT II approaches with a DH of 100 feet and a visibility minimum as low as RVR 1200 at runways with
reduced lighting for operators with a CAT III operational authorization and based on CAT III airborne equipment.
b) In 2009, Order 8400.13D introduced criteria authorizing CAT II operations to an RVR 1000 to runways with standard CAT II equipment and lighting when using autoland or HUD
to touchdown. These operations were normalized by the publication of AC
2018, and are now considered a subset of standard CAT II minima.
C. Evolution of CAT III Operations.
1) Initial Step in Introducing CAT III Operations. In 1966, at an ICAO Communications/Operations meeting, international CAT III ground and airborne
equipment standards were established. These standards were integral in the maturation of CAT III ground equipment, airborne equipment, and operating concepts.
2) Initial U.S. CAT III Criteria. The initial U.S. CAT III criteria were issued via AC 120-28, Criteria for Approval of Category III Weather Minima for
Takeoff, Landing, and Rollout, in September 1969, to assist industry in developing CAT III capability. These criteria were based on the CAT I and CAT II building blocks, and underscored
the requirement for further improvements in ground-based NAVAIDs, RVR reporting capabilities, airborne equipment, maintenance standards, and pilot training and qualification. The criteria
were intended to support operations termed “CAT IIIa,” which employed minima as low as RVR 700 using autoland systems. These operations required a DH but no visual segment.
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.
3) Initial CAT III Approvals. The publication of initial CAT III criteria led to the rapid development of CAT IIIa airborne and ground-based capabilities
to facilitate minima as low as RVR 700. In February 1971, the B747 was granted the first U.S. type design approval for CAT IIIa. This type design approval was based on the use of fail
operational (FO) automatic landing systems. CAT IIIa criteria were significantly improved in December 1971 by the publication of AC 120-28A, Criteria for Approval of Category IIIa Landing
Weather Minima. This revision enhanced the type design approval (airworthiness certification) 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.
4) Type II ILS-Equipped Runways and Fail Passive (FP) Airborne Equipment. The criteria initially established for CAT IIIa were based on a conservative
approach to reducing operating minima.
a) 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, research efforts in the United States and Europe supported the conclusion that, under tightly controlled conditions, FP CAT III operations could be safely conducted.
b) In October 1976, the FAA established approval criteria for FP CAT IIIa autoland operations using DH 50/RVR 700. In December 1976, the B727 became the first airplane
certificated by the United States for FP CAT IIIa operations. AC 120-28B, Criteria for Approval of Category IIIa Landing Weather Minima, 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 B727 and DC-9 airplanes.
c) Today, all systems supporting CAT II or CAT III operations (i.e., Mark 20 systems) meet the integrity requirements of a Type III system. While the lowest original
landing minimum authorized for CAT IIIa by U.S. operators at any airport was RVR 700, this was later reduced to RVR 600 in order to harmonize U.S. CAT IIIa standards with ICAO.
5) 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, Criteria for Approval of Category III Landing Weather Minima). While this revision described CAT IIIb
operations with minima below RVR 700 but no lower than RVR 150, the lowest minima authorized for CAT IIIb was RVR 300. The B767 became the first aircraft certificated (type design approval)
for CAT IIIb by the United States. The B767 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.
a) 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 any visual references necessary for the various CAT III operations.
b) The first U.S. CAT IIIb operational approvals were granted to Trans World Airlines (L-1011) and Eastern Airlines (L-1011 and A300) using minima of RVR 600. RVR 600 was
initially 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 taxiway centerline 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 (KSEA) in 1987.
6) CAT III Terminology. In 2012, the FAA began phasing out the use of the terms “CAT IIIa,” “CAT IIIb,” and “CAT IIIc” in
favor of a performance-based approach using only the term “CAT III” to describe all operations below RVR 1000. Although the outdated terms may still be found on some approach charts,
they are no longer used in aircraft certification or operational authorization.
7) Pilot in the Active Control Loop. A conceptual change was introduced by AC 120-28C, published in March 1984. This update established concepts for CAT III operations
with the “pilot in the active control loop.” This concept permitted manually flown CAT III operations using special flight guidance and control systems such as HUDs. In 2018, AC
this concept by allowing authorizations based on hybrid systems, consisting of a FP autoland system used in combination with a monitored HUD flight guidance system (FGS).
4-149 AIRBORNE EQUIPMENT AND GROUND INFRASTRUCTURE. Historically, each new increment of lower landing minima has required costly improvements in ground-based NAVAIDs
and runway infrastructure (e.g., ILS signal integrity improvements, RVR sensor installations, and approach and runway lighting). In more recent years, advancements in head-up guidance systems, vision
systems, space-based and performance-based navigation systems, and other advancements have enabled a divergence from this paradigm, allowing credit for the use of airborne systems in lieu of ground
infrastructure to achieve lower landing minima. Recent changes allowing GLS and LPV minima equal to those of CAT I ILS, as well as the advent of RVR 1800 with reduced lighting, SA CAT I, SA CAT II,
and EFVS operations are all examples of this approach. In general, this trend of more reliance on cockpit-based systems as a substitute/replacement for ground-based infrastructure is expected to continue.
4-150 AIRPORT FACILITIES AND SERVICES. The varied seeing conditions encountered in AWO require pilots to rely heavily on visual aids, electronic guidance, vision systems,
other onboard systems, and other facilities and services provided by the airport. Therefore, basic visual flight rules (VFR) airport facilities and services must typically be enhanced before safe operations
can be conducted in instrument flight conditions. Historically, the authorization of lower minima has required improved ground infrastructure (e.g., approach and runway lighting systems, far field monitor,
and additional RVR sensors) in order to achieve an Acceptable Level of Safety (ALoS). However, with the proliferation of some modern and emerging cockpit technologies, authorizations have been granted with
less reliance on ground infrastructure in favor of more capable and reliable onboard equipment (e.g., HUD, vision systems, FD, and radio altimeter (RA)). Examples of these authorizations include SA CAT I
and II as well as CAT I RVR 1800 operations with reduced lighting and EFVS operation in accordance with part
Nonetheless, runways and taxiways typically must still meet stringent criteria with respect to width, length, marking, and lighting. Instrument approach aids and IAPs are required. 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.
RESERVED. Paragraphs 4-151 through 4-170.