12/21/15

 

8900.1 CHG 225

VOLUME 4  AIRCRAFT EQUIPMENT AND OPERATIONAL AUTHORIZATION

CHAPTER 2  ALL WEATHER TERMINAL AREA OPERATIONS

Section 7 Safety Assurance System: Category III Operations

4-331    OVERVIEW. This section contains concepts, direction, and guidance to be used by principal inspectors (PI) for evaluating and approving or denying requests for authorization to conduct all Category (CAT) III operations. This includes all CAT III operations at airports and runways new to an operator/program manager, even though previously approved aircraft, airborne equipment, ground-based equipment, concepts, and procedures are being used in these operations. Additional information may be found in Volume 4, Chapter 2, Section 1.

4-332    APPLICABILITY. The intent is that the PI will use the general information provided in this section, along with the specific information provided in Volume 4, Chapter 2, Section 2 for domestic operators and Volume 4, Chapter 2, Section 8 for Title 14 of the Code of Federal Regulations (14 CFR) part 129 foreign air carriers when evaluating requests for CAT III operations. This process is only applicable for operator requests for instrument landing system (ILS)-based CAT III operations. Requests for other than ILS-based CAT III should be forwarded to the regional Flight Standards division (RFSD) Next Generation (NextGen) Branch (AXX-220).

4-333    REPORTING SYSTEMS.

A.    Safety Assurance System (SAS). The PI will utilize SAS Data Collection Tools (DCT) 2.2.2, Category II & III Ops, and 2.3.1, Appropriate Operational Equipment.

B.    Program Tracking and Reporting Subsystem (PTRS). The PI will utilize PTRS activity codes.

·    CAT II/III ILS Operations Phase I Approval: 1430.

·    CAT II/III ILS Operations Phase II Approval: 1431.

·    CAT II/III ILS Operations Phase III Approval: 1432.

·    CAT II/III ILS Operations Phase IV Approval: 1433.

·    CAT II/III ILS Operations Phase V Approval: 1434.

4-334    REFERENCES, FORMS, AND JOB AIDS.

A.    References (current editions):

·    Title 14 CFR Parts 91, 97, 119, 121, 125, 129, and 135.

·    FAA Order 6750.24, Instrument Landing System and Ancillary Electronic Component Configuration and Performance Requirements.

·    FAA Order JO 7110.65, Air Traffic Control.

Indicates new/changed information.

·    FAA Order JO 7210.3Y, Facility Operation Administration.

·    FAA Order 8260.49, Simultaneous Offset Instrument Approach (SOIA).

·    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.

Indicates new/changed information.

·    Advisory Circular (AC) 25-7, Flight Test Guide for Certification of Transport Category Airplanes.

·    AC 97-1, Runway Visual Range (RVR).

·    AC 120-28, Criteria for Approval of CAT III Weather Minima for Takeoff, Landing and Rollout.

·    AC 120-29, Criteria for Approval of Category I and Category II Weather Minima for Approach.

·    AC 120-57, Surface Movement Guidance and Control System.

Indicates new/changed information.

·    AC 120-71, Standard Operating Procedures for Flight Deck Crewmembers.

·    Technical Standard Orders (TSO).

·    U.S. Flight Information Publications (FLIP).

B.    Forms. None.

C.    Job Aids. PIs of parts 121 and 135 Operators will utilize DCTs 2.2.2, Category II & III Ops, and 2.3.1, Appropriate Operational Equipment.

4-335    DEFINITIONS.

A.    Category (CAT) III Operations. CAT III operations are separated into three subcategories: CAT IIIa, CAT IIIb, and CAT IIIc.

B.    CAT IIIa Operations. CAT IIIa is an approach and landing operation with a Runway Visual Range (RVR) of not less than 700 feet (200 meters) without a decision height (DH), or with a DH of less than 100 feet (30 meters), or an alert height (AH), which is typically between 50 and 200 feet, depending on aircraft certification and operator preferences. Both fail passive (FP) and fail operational (FO) airborne equipment can be used in CAT IIIa operations.

C.    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. Presently, the lowest FAA-approved minimum for any CAT III operations is RVR 300 (75 meters) due to difficulties in accomplishing safe ground movement for both aircraft and ground safety services, such as Aircraft Rescue and Fire Fighting (ARFF).

D.    CAT IIIc Operations. CAT IIIc is an approach and operation landing without a DH and without RVR limitations (zero-zero). CAT IIIc operations are currently not authorized.

4-336    APPROVAL METHOD.

A.    Part 91 and Part 125 Letter of Deviation Authority (LODA) Holder. A part 91 (including part 91 subpart F) or 125 LODA holder operator is issued a letter of authorization (LOA) for all CAT III operations using the C060 in Web-based Operations Safety System (WebOPSS).

B.    Part 91 Subpart K (Part 91K). A part 91K operator is issued a management specification (MSpec) for all CAT III operations using C060 in WebOPSS.

C.    Parts 121, 125, 129, and 135. Part 121, 125, 129, or 135 operators are issued operations specification (OpSpec) C060 for all CAT III operations (or H109 for helicopter operations) in WebOPSS.

4-337    GENERAL.

A.    Concepts, Direction, and Guidance. This section contains concepts, direction, and guidance to be used by inspectors for evaluating and approving or denying requests for authorization to conduct CAT III All Weather Terminal Area Operations (AWTA). All CAT III operations using aircraft, airborne equipment, ground‑based equipment, or concepts/procedures, which are new to a particular operator, require approval. In addition, all CAT III operations at airports and runways new to a particular operator require approval even though previously approved aircraft, airborne equipment, ground-based equipment, concepts, and procedures are used in those operations. This section contains an amplification of the general concepts, policies, direction, and guidance covered in previous sections of this chapter. Specific standards are provided for inspectors evaluating CAT III AWTAs with airborne and ground-based equipment, which have well understood operational characteristics and limitations. In cases where an operator requests approval to conduct CAT III AWTAs using equipment, concepts, and/or procedures not addressed in these standards, a request for policy and guidance must be forwarded through the appropriate RFSD NextGen Branch (AXX-220) to the Flight Technologies and Procedures Division (AFS‑400).

Indicates new/changed information.

B.    Types of CAT III Operations. The only types of CAT III operations that can be currently authorized (as of 2010) for use by U.S. operators are ILS based. CAT III operations using Global Positioning System (GPS) Landing Systems (GLS), which requires the use of a Ground Based Augmentation System (GBAS) or Local Area Augmentation System (LAAS), may also be approved in the near future.

C.    Objective of CAT III Operations. The essential difference between CAT III AWTAs and CAT I and II operations is that a CAT III operation places a greater reliance on the guidance provided by the airborne and ground-based guidance equipment. The guidance provided by the equipment must continue through touchdown in CAT IIIa operations and through touchdown and rollout to a safe taxi speed in CAT IIIb operations. In contrast to other types of operations, CAT III operations do not ensure sufficient external visual cues for the pilot to manually control the aircraft during flare and landing. The primary objective of CAT III operations is to provide a level of safety equivalent to CAT I and CAT II operations without the use of these visual cues. The desired level of safety for CAT III operations is achieved by the following enhancements:

1)    The airborne equipment and ground-based equipment must ensure increased precision in flightpath control. The increased reliability and precision of flightpath control (as compared to CAT I systems) is achieved through highly reliable and precise ground-based equipment and airborne systems. These systems are capable of guiding the aircraft with significantly increased precision to touchdown or through rollout, as appropriate.
2)    The aircraft performance and equipment requirements associated with a missed approach from very low altitudes are enhanced to ensure that these operations can be safely conducted even if a momentary touchdown occurs on the runway after the go-around is initiated. Special criteria assures obstacle and terrain clearance to accommodate missed approaches from very low altitudes.
3)    More stringent criteria are specified for the profile of the pre-threshold terrain to ensure that the flight guidance and control systems function properly during the final stages of approach, flare, and landing.
4)    Surface Movement Guidance and Control Systems (SMGCS) are established to ensure the landing runway is protected from potential incursions and ensure the overall safety of the operation.

4-338    CAT III OPERATIONAL CONCEPTS. The weather and environmental conditions encountered in CAT III AWTAs severely restrict seeing conditions. External visual reference is not acquired until the aircraft reaches a very low altitude. Typically, external visual references begin to become available below 100 feet. Even though external visual references are usually available before touchdown, the seeing conditions are not sufficient for the pilot to consistently perform a safe, manual landing. Therefore, the aircraft must be controlled by instruments and special equipment throughout the approach, flare, and touchdown (deceleration for rotorcraft) in weather conditions as low as RVR 700 and through rollout to a safe taxi speed (air taxi or hover for rotorcraft) in weather conditions below RVR 700. Due to the reduced seeing conditions and the hazards associated with a pilot’s attempts to manually maneuver the aircraft to landing in those seeing conditions, the precision of the flight guidance and control system and the overall precision of flightpath control must provide these capabilities.

A.    DH and AH. There are substantial differences between the DH and AH concepts. All FP operations are conducted in accordance with the DH and RVR concepts. All FO operations are normally conducted in accordance with the AH and RVR concepts. DHs are only used with FO systems in very unique situations (refer to AC 120-28). DH and AH are never used together in any operation since the DH requires that external visual reference be established before passing a specified point and AH does not. The very limited seeing-conditions available in CAT III operations require additional criteria to ensure that an adequate level of safety is achieved and maintained when operating in this environment.

1)    DH Operations. For FP operations using a DH, the pilot must arrive at a decision before passing the DH to either permit the flight guidance and control system to be used to touchdown or to execute a missed approach. For a DH operation, the external visual information, the instrument information, and the airborne system information must be integrated so the flightcrew can make a definitive decision no later than arrival at the DH. The decision to permit the flight guidance and control system to continue to direct the aircraft to touchdown must be based on an assessment that the airborne systems have not degraded in a way that affects FP capabilities, and the external visual cues (touchdown zone (TDZ) lighting) confirm that the aircraft will touchdown within the TDZ. Since all DHs used in CAT III operations must be 50 feet or less, the inner marker (IM) cannot be used to define the CAT III DH. Since DH 50 is located very near the runway threshold, the terrain profile within these areas is adequate for CAT III radio altimeter (RA)-based DHs. CAT III operations are normally conducted using a DH of 50 feet; however, a different DH may be operationally approved in special circumstances, such as the use of a hybrid CAT III landing system.
2)    AH Operations. For operations with an AH, the pilot must also arrive at a decision, before passing the AH, to either permit the flight guidance and control system to be used to touchdown or to execute a missed approach. In direct contrast to operations with a DH, however, this decision must be based on an assessment that the airborne systems have not degraded in a way that affects FO capabilities. FO systems permit certain system failures below AH without requiring a missed approach, because the aircraft is still capable of continuing to a safe landing and rollout. External visual references are not required before touchdown in operations based on the AH concept.

B.    Kinds of CAT III Operations. There are two different and distinct kinds of CAT III operations: FP operations and FO operations.

1)    FP operations use a DH of 50 feet (15 meters) and a TDZ RVR no lower than RVR 600 (175 meters). In the event of a failure when using a FP CAT III system, the flight guidance and control system will not disturb the aircraft’s flightpath when it fails, and the flightcrew immediately receives an aural and visual warning of system failure. Therefore, a DH must be used to ensure that, before passing 50 feet above ground level (AGL), the flightcrew establishes external visual reference with the TDZ to determine that the flight guidance and control system is functioning properly and to ensure that the aircraft will land within the TDZ. A go-around is mandatory if the flight guidance and control system fails before touchdown during FP operations in CAT III weather conditions.
2)    FO operations usually use an AH instead of a DH (refer to AC 120-28). As the name implies, critical CAT III systems remain operational even if some failures occur. FO systems are designed so that the system remains fully operational following any failure or combination of failures that are likely to occur after the aircraft passes AH. Therefore, there is no requirement to establish external visual reference before touchdown to confirm that the aircraft will land safely. The lowest minimum that may currently be approved for any AWTA by a U.S. operator is RVR 300 (90 meters). This restriction is based on the difficulties associated with aircraft movement on the taxiways, ramps, and other maneuvering areas on the airport and the difficulties related to providing timely safety facilities and services (such as ARFF).

C.    CAT III Operating Minimums. CAT III operating minimums are based on two criteria and are always the higher of the following minimums:

1)    Published ILS Minimums. The part 97 Standard Instrument Approach Procedure (SIAP) criteria is based on the integrity and reliability of the ILS ground system. When the ILS supports operation to touchdown but not rollout, RVR 700 is the lowest authorized minimum. When the ILS supports both touchdown and rollout operations, RVR 600 minimums are typically published. If the ILS supports both touchdown and rollout operations and the Localizer (LOC) is monitored to an even higher standard of reliability, RVR 300 minimums may also be published.
2)    CAT III OpSpec/MSpec/LOA C060 Minimums. CAT III minimums in C060 are based on the certification statement in the Aircraft Flight Manual (AFM), and based on the airworthiness requirements contained in the appropriate revision of AC 120-28.
3)    AC 120-28C-Authorized Aircraft. Aircraft authorized under AC 120-28C and earlier typically contain a statement authorizing CAT IIIa or CAT IIIb automatic approach and landing operations.
a)    Aircraft authorized for CAT IIIa are currently limited to RVR 700 for TDZ and RVR 700 for Mid Runway Rollout (MID) by regulation, unless the AFM also contain statements authorizing FP landing systems. The aircraft may then be authorized RVR 600 for TDZ, RVR 600 for MID, and RVR 300 for rollout.
b)    Aircraft authorized for CAT IIIb with a rollout control system that meets the criteria in AC 120‑28, Appendix 2 (FP rollout system) may be authorized minimums as low as RVR 400 for TDZ, RVR 400 for MID, and RVR 300 for rollout.
c)    Aircraft authorized for CAT IIIb with a rollout control system that meets the criteria in AC 120‑28, Appendix 3 (FO rollout system) may be authorized minimums as low as RVR 300 for TDZ, RVR 300 for MID, and RVR 300 for rollout.
d)    AC 120-28D-Authorized Aircraft. Aircraft authorized under AC 120-28D or subsequent revisions contain a statement authorizing FP or FO landing and/or rollout control systems.
e)    FP Landing System without Rollout System. Aircraft with an FP landing system without a rollout system may be authorized minimums as low as RVR 600 for TDZ, RVR 600 for MID, and RVR 300 for rollout.
f)    FP Landing System with Any Rollout System. Aircraft with a FP landing and rollout system may be authorized minimums as low as RVR 600 for TDZ, RVR 400 for MID, and RVR 300 for rollout.
g)    FO Landing System with a FP Rollout System. Aircraft with an FO landing system and FP rollout systems may be authorized minimums as low as RVR 400 for TDZ, RVR 400 for MID, and RVR 300 for rollout RVR.
h)    FO Landing System with a FO Rollout System. Aircraft with FO landing and rollout systems may be authorized minimums as low as RVR 300 for TDZ, RVR 300 for MID, and RVR 300 for rollout RVR.

4-339    RA AND PRE-THRESHOLD TERRAIN.

A.    Operation. The operation of almost all CAT III landing systems is dependent on RA information during the latter stages of the landing. The flare profile, the rate of descent at touchdown, and the distance of the touchdown point from the threshold can be adversely affected by the profile of the terrain immediately before the landing threshold. The terrain, which is most critical, lies in an area approximately 200 feet on either side of the runway centerline (RCL) extended from the threshold into the approach area to a distance of approximately 1,000 feet before the landing threshold.

B.    Pre-threshold Terrain. At runways where the terrain beneath the approach flightpath is not approximately level, abnormal autopilot (AP) and/or flight director (FD) behavior may result from erroneous RA signals. Irregularities in the pre-threshold terrain can have a major effect on the performance of the landing systems required for CAT III operations (autoland or Head-Up Display (HUD) to touchdown). A special operational test and evaluation program is required before approving any CAT III operations for any aircraft on these runways. This test program is essential to ensure that CAT III operations can be safely conducted on these runways with a particular CAT III aircraft type (aircraft with similar flight characteristics and similar flight guidance and control systems). This special test and evaluation must be accomplished in nonrevenue service.

C.    Requests for Evaluation. All requests to conduct this evaluation must be sent to the RFSD NextGen Branch (AXX-220) for approval. Inspectors shall not, under any circumstances, authorize any CAT III operations with any aircraft to these runways unless that particular CAT III type aircraft has been specifically evaluated in accordance with AC 120-28 and specifically approved for that operation by the RFSD. The Flight Operations Branch (AFS-410) maintains a list of these special terrain runways which must be authorized in OpSpec/MSpec/LOA C059 and/or C060 to utilize any CAT II/III minimums that require the use of autoland or HUD to touchdown. This document lists all CAT II/III special terrain runways in the United States, as well as all approved aircraft make, model, and series (M/M/S) for each runway. This list is available on the AFS-410 public Web site at http://www.faa.gov/about/office_org/headquarters_offices/avs/offices/afs/afs400/afs410/status_lists/. See Volume 4, Chapter 2, Section 2 and AC 120-28 for more information about authorizing CAT II/III operations at special terrain runways.

D.    Runways. A few CAT II runways currently have restrictions (i.e., Radio Altitude minimums Not Authorized (RA NA)) due to the pre-threshold terrain profile, which prohibits the use of RA information to determine the CAT II DH. Standard CAT II operations (DH 100 and RVR 1200) can still be conducted by using the IM to determine arrival at the DH. Although the RA cannot be used to accurately and reliably determine arrival at the CAT II DH (height above touchdown (HAT) 100), it may still be possible to safely conduct CAT III operations to these runways if the pre-threshold terrain does not adversely affect the performance of the CAT III landing system. For example, Pittsburgh International Airport (KPIT) runway 10L has a CAT II approach with “RA NA” minimums (RA DH not authorized), but certain aircraft have been approved for CAT III autoland operations.

4-340    FUTURE REDUCTIONS TO LANDING MINIMUMS. The lowest landing minimum currently authorized for CAT III operations by U.S. operators at any airport and by foreign air carriers in the United States is RVR 300. This restriction is related primarily to problems associated with aircraft taxi operations and the difficulty of providing adequate safety services (such as crash, fire, rescue, and collision prevention) when operating in seeing-conditions less than RVR 300. The lowest minimum currently authorized for foreign air carriers outside the United States is 75 meters (RVR 300) and is based on an operational determination similar to the U.S. RVR 300 decision. Future reductions in landing minimums are unlikely until technology permits the development of economically viable capabilities to adequately resolve these limitations. Presently potential solutions appear to be enhancements in airborne equipment such as forward-looking infrared or millimeter wave radar technologies.

4-341    FOREIGN CAT III INSTRUMENT APPROACH PROCEDURES (IAP).

A.    Operations. All CAT III operations by U.S. operators at foreign airports must be authorized in accordance with the guidance and direction in this order. All foreign runways approved for CAT III operations by U.S. operators must also meet the requirements of this order and the current edition of 8260.31, Foreign Terminal Instrument Procedures.

B.    Foreign Equivalence. Although it is recognized that the CAT III ground-based systems and procedures at foreign airports may not be in exact accordance with U.S. standards, it is critical for the foreign airports to provide the information and functions that are necessary for CAT III operations in a manner consistent with the intent of U.S. CAT III standards.

C.    General. The FAA region, which has surveillance responsibility for a particular foreign airport, has the responsibility for evaluating any runway at that airport which supports CAT III operations. The controlling region is also responsible for evaluating these CAT III runways in accordance with Order 8260.31 and for recommending approval or disapproval of CAT III operations to those runways. The controlling region’s recommendations must be forwarded to AFS-400 for further evaluation and final approval or disapproval.

Note:  Foreign runways that have been determined to be equivalent to U.S. CAT III standards and approval for CAT III operators are identified in the list of runways maintained by AFS-400. Operators desiring CAT III approvals at foreign airports that are not on this approved list should submit a request for evaluation and approval through their principal operations inspector (POI) to the RFSD NextGen Branch. The controlling region’s NextGen Branch will conduct an evaluation. Upon successful completion of the evaluation, the NextGen Branch will notify AFS-400 for final approval and addition to the approved list.

D.    Determining Equivalence. The major factor that is considered by the controlling region in approving foreign runways in accordance with Order 8260.31 for CAT III operations by U.S. operators is the degree of equivalence with U.S. CAT III standards. This determination evaluates the equivalence of:

·    High-intensity approach lights;

·    High-intensity runway edge lights;

·    TDZ and RCL lights;

·    Taxiway edge lights;

·    High-intensity taxiway centerline lights;

·    Runway markings;

·    The quality and integrity of the approach and landing ground-based guidance system;

·    The RVR reporting capabilities and procedures;

Indicates new/changed information.

·    ILS critical areas, including signs and markings;

·    Obstacle clearance protection in the approach and missed approach, including the obstacle-free zone;

·    Airport surface traffic control;

·    Terminal area air traffic control (ATC); and

·    Procedures for regulating the ground movement of aircraft and vehicles during CAT III operations.

E.    Authorizing Foreign CAT III Runways. All CAT III operations conducted in foreign countries must be conducted in accordance with the operator’s CAT III OpSpecs. The only means of approving these operations is through the issuance of OpSpecs, which specify the foreign runways and minimums authorized for each aircraft used by the operator. OpSpecs C060 and H109 specify the CAT III IAPs, runways, operating minimums, limitations, and aircraft authorized for CAT III operations for a particular operator. These paragraphs also specify the CAT III airborne equipment, RVR equipment, pilot qualification, and missed approach requirements that apply to the operator’s CAT III operation. If the flightcrew is properly qualified and the aircraft is properly equipped and maintained, an operator can, in general, be authorized to conduct CAT III AWTAs to any foreign runway approved for CAT III operations. The exception to this are those runways specified as restricted CAT III runways. The criteria in AC 120-28 and this order establish the lowest approach and landing minimums that can be authorized, under any circumstances, for CAT III operations. The lowest minimums for each kind of CAT III operation for a particular operator are specified in OpSpecs C060 and H109, as appropriate. FAA inspectors shall not authorize an operator to use minimums lower than these values. Additionally, inspectors shall not authorize the use of CAT III minimums for any foreign runway unless the provision of this order and Order 8260.31 are met.

4-342    CAT I AUTOLAND OR HUD TO TOUCHDOWN OPERATIONS. Autoland or HUD to touchdown operations are required for all CAT III operations, and many operators use autoland or HUD for CAT II, CAT I, and visual flight rules (VFR) operations as well. Part 121, § 121.579(c); part 125, § 125.329(d); and part 135,
§ 135.93(d) prohibit the use of autoland or HUD to touchdown in any operation unless the operator is specifically authorized via OpSpecs. OpSpec C059 and C060 authorize autoland or HUD to touchdown in CAT II and CAT III operations, respectively. OpSpec C061 or H110 authorizes autoland operations in other than CAT II/III operations and OpSpec C062 or H111 authorizes HUD to touchdown in other than CAT II/III operations.

A.    ILS Category Classification. The ILS category classification system provides a more comprehensive method of describing ILS performance than the simple CAT I/II/III classification. ILS facility classification is described in Order 6750.24. A facility’s classification is defined by using two characters (I/C, II/D, III/E, etc.). facility’s classification is defined by using two characters (I/C, II/D, III/E, etc.).

1)    The first character indicates conformance to the facility performance category standards. This character indicates if the ground equipment is classified as a CAT I, CAT II, or CAT III ILS.
2)    The second character defines the ILS point (Figure 4-21A, Localizer Course and Glidepath Bend Amplitude Limits) to which the LOC conforms to the Facility Performance CAT III course structure tolerances. These classifications indicate ILS conformance to a physical location on the approach or runway as follows:

·    A: 4 NM before the threshold.

·    B: 3,500 feet before the threshold (CAT I decision point).

·    C: Glidepath altitude of 100 feet height above threshold (HATh) (CAT II decision point).

·    T: Threshold.

·    D: 3,000 feet beyond the threshold (CAT III requirement only).

·    E: 2,000 feet before the runway end (CAT III requirement only).

Figure 4-21A.  Localizer Course and Glidepath Bend Amplitude Limits

Figure 4-21A. Localizer Course and Glidepath Bend Amplitude Limits

B.    Use of Autoland at U.S. CAT I Facilities or Equivalent. For CAT I, autoland may typically be used at runways with facilities other than those with published CAT II or III IAPs. This is to aid pilots in achieving stabilized approaches and reliable touchdown performance to improve landing safety in adverse weather; for CAT II or III training; to exercise the airborne system to ensure suitable performance; for maintenance checks; or for other such reasons. Use of this capability may be particularly important for pilot workload relief in stressful conditions of fatigue after long international flights; night approaches; crosswinds or turbulence; when there may be other aircraft non-normal conditions being addressed; or to aid safe landing performance in otherwise adverse weather, in restricted visibility, or with cluttered runways. This is true even though reported visibility may be well above minimums (e.g., heavy rain distorting view out the windshield, snow covered runways where markings are not easily visible, etc.).

C.    ILS Classification and CAT I Autoland Operations. ILS classification is being added to the Airport/Facility Directory (A/FD), but not all ILS runways are included as of August 2010. To support autoland or HUD to touchdown operations, CAT III course structure tolerances to at least point D are preferred (e.g., I/D, II/D, III/D). In 2010, all published CAT II and III approaches in the United States meet this standard. CAT II approaches that do not support autoland operations will note this limitation via a chart note or Notice to Airmen (NOTAM). When conducting autoland operations on a CAT I runway/ILS, runways with an I/D or I/E classification are the most suitable and are preferred. Practice autoland or HUD to touchdown operations may be conducted at CAT I runways in CAT I or better weather conditions where the facility classification is unknown, because the flightcrew is monitoring system performance, visually verifying the position of the aircraft, and can determine whether to continue to a landing or execute a missed approach in CAT I or better weather conditions. Though it is not recommended, flightcrew monitoring and increased visibility also permits practice autoland or HUD to touchdown operations using an ILS classified as I/A, I/B, I/C, or I/T, provided the operation is performed in VFR conditions. The FAA maintains an information-only list of ILS classification status at http://avnwww.jccbi.gov/pls/datasheet_prd/PRO_ilsperform_rpt.

D.    Pre-Threshold Terrain.

1)    AFS-410 maintains a list of CAT II/III runways with special terrain which may affect autoland or HUD to touchdown operations, such as irregular pre-threshold terrain or TDZ slope. This list is available at http://www.faa.gov/about/office_org/headquarters_offices/avs/offices/afs/afs400/afs410/status_lists/. Each operator and aircraft must be approved for each special terrain runway to conduct any CAT II or III operations using autoland or HUD to touchdown. Volume 4, Chapter 2, Section 2 contains more information about how to authorize CAT II/III operations at special terrain runways.
2)    The FAA does not analyze CAT I runways to determine if any irregular pre-threshold terrain will impact autoland or HUD to touchdown operations. Practice autoland or HUD to touchdown operations may be conducted at CAT I runways where the pre-threshold terrain has not been analyzed because the flightcrew is monitoring system performance, visually verifying the position of the aircraft, and can determine whether to continue to a landing or execute a missed approach in VFR conditions. All operators approved to use autoland- or HUD-equipped aircraft should be encouraged to routinely use these systems at suitably equipped runways during operations in VFR and in CAT I instrument flight rules (IFR) conditions. Flightcrew training should emphasize the importance of monitoring equipment performance on all practice autolands.

E.    Maintenance Return to Service and Required Practice Autolands. An aircraft manufacturer and certification requirements may require that a practice autoland or HUD to touchdown be performed on a published CAT II or III approach. If so, the operator should adhere to these requirements. If autoland is not required to be performed on a CAT II ILS, it is important to note that an unsatisfactory approach is extremely difficult to attribute to small errors in ILS ground equipment. Even CAT I ILS facilities that meet CAT III signal standards are not monitored to the same tolerances as CAT II/III facilities. An unsatisfactory approach due to a critical error incursion is something that may be identified, but an unsatisfactory approach due to a signal or monitor error cannot be detected by the flightcrew or maintenance.

F.    Flightcrew Training. In addition to other training requirements, flightcrew training should emphasize the importance of:

1)    Monitoring equipment performance and visual verification of aircraft position on all practice autolands.
2)    Verifying that the CAT I approach does not have any charted restrictions, which would prohibit autoland or HUD to touchdown operations (“ILS unusable within 0.5 DME,” “autopilot coupled approach not authorized below XXX feet”).
3)    Requesting that ATC protect the critical area for all practice autolands. ATC will protect the ILS critical areas if the ceiling is less than 800 feet and/or the visibility is less than 2 miles.
4)    Performing maintenance return to service as required by either the manufacturer, certification, or the operator, as described in subparagraph 4-342E.

4-343    CAT II/III ILS OUTAGES AND CONTINUITY OF SERVICE (CoS) REQUIREMENTS.

A.    Purpose. CAT II/III operations rely on high-integrity LOC and glideslope (GS) signals with a low probability radiated signal interruption (CoS). ILS design and approval criteria address required system integrity. The current edition of FAA Order JO 6750.57, Instrument Landing System Continuity of Service Requirements and Procedures, contains the policy and requirements for Technical Operations (Tech Ops) to meet CoS requirements for CAT II/III ILS facilities, including CAT II/III ILS downgrade and reinstatement criteria. The RFSD NextGen Branch (AXX-220) is the Flight Standards Service (AFS) point of contact (POC) for ILS CoS issues. AFS-400 is responsible for ILS CoS policy, guidance, and support. This section summarizes ILS CoS requirements relevant to inspectors and summarizes some of the relevant Tech Ops requirements. Refer to Order JO 6750.57 for current ILS CoS criteria, Order 6750.24, and Order 8400.13 for current AFS ILS facility requirements.

B.    Definitions.

1)    Continuity of Service (CoS). The quality that relates to the rarity of radiated signal interruptions. The level of CoS of the LOC or the glidepath is expressed in terms of the probability of not losing the radiated guidance signals.
2)    CoS Outage. Any reportable LOC or GS unscheduled interruption for which there was an unexpected cessation of the radiated signal, regardless of cause, or any failure of a LOC or GS to properly initiate radiation, such as when an ILS fails to radiate upon a runway interlock selection.
3)    CoS Mean Time Between Outages (MTBO). Average number of hours between countable CoS outages, considering only the last five in-service periods. This MTBO calculation does not include consideration of all interruptions as is typical in National Airspace Performance Reporting System (NAPRS) reporting. Rather, it represents the MTBO outlined in International Civil Aviation Organization (ICAO) Annex 10.
4)    Instrument Landing System (ILS) CoS Office of Primary Responsibility (OPR). A single, functional entity within the technical services organization of each service area, consisting of one or more designated ILS experts. The ILS CoS OPR is responsible for analyzing and monitoring ILS CoS throughout the entire service area and recommending actions to best ensure that MTBO requirements are met.
5)    Predicted MTBO. The CoS MTBO if an outage occurred at the time of the calculation.
6)    Projected MTBO. The CoS MTBO projected out 3 months from the predicted MTBO.

C.    ILS Outage and Downgrade Requirements. Tech Ops maintains a comprehensive database, which contains the outage history and up-to-date MTBO for all ILS facilities in the United States. Order JO 6750.57 requires an ILS facility to be downgraded based on the number of outages in the preceding 6 months. As a result, Tech Ops and Navigation Services escalate their priorities and involvement in repairs at facilities that accrue multiple outages over a short period of time.

1)    When Tech Ops downgrades a facility, the corresponding ILS landing minimum is also taken out of service via NOTAM:
a)    Fourth outage in the preceding 6 months: CAT III RVR 300 minimum not authorized.
b)    Fifth outage in the preceding 6 months: All CAT III minimums not authorized.
c)    Sixth outage in the preceding 6 months: All CAT II and CAT III minimums not authorized.
2)    This outage count applies to the separate LOC and GS systems, not the sum of the outages for each system. For example, a LOC which has its fifth outage in the preceding 6 months will lose all CAT III minimums. An ILS with three LOC outages and three GS outages is not downgraded, because neither the LOC nor the GS individually have four or more outages in the preceding 6 months. (See Table 4-8, Outage Consequences.)
3)    Order JO 6750.57 is clear that downgrades are required as a result of excessive outages in the preceding 6 months. Tech Ops will notify the appropriate NextGen Branch (AXX-220) of a downgrade due to outages, and will not waive any ILS downgrade requirements except as allowed in Order JO 6750.57. Due to the strong emphasis on system reliability to support CAT II/III landing operations, the RFSD NextGen Branch should not consider waivers to ILS downgrades as a result of excessive outages.

D.    ILS Reinstatement After a Downgrade. To reinstate an ILS landing minimum, Tech Ops repairs the ILS facility, verifies CAT II or III capability (as applicable), and first restores CAT I landing minimums. After the system demonstrates sufficient reliability by operating outage free for a fixed period of time, lower landing minimums are then reinstated as authorized in Order JO 6750.57. After any downgrade, the ILS must operate without an outage for 4 weeks to restore the next lower landing minimum. To restore each additional lower landing minimum, the system must operate outage free for an additional 2 weeks for each minimum to reinstate. See Table 4-8A, Instrument Landing System Reinstatement Periods, for examples of ILS reinstatement after a downgrade.

E.    MTBO Requirements. Unlike downgrades as a result of excessive outages in the preceding 6 months, Order JO 6750.57 does not require a downgrade if a LOC or GS MTBO falls below the hours required in Order 6750.24 and Order 8400.13. Instead, a downgrade is at the discretion of AFS, in coordination with Tech Ops. This is because MTBO is very useful as a trend analysis number, but averaging the time periods between outages can be misleading in specific circumstances.

1)    The calculation of MTBO is the average number of hours between countable CoS outages, considering only the last five in-service periods, as shown in Figure 4-22, Active Periods Between Outages.
2)    While MTBO provides a very useful tool for trend analysis, very large or very small numbers can skew the entire MTBO up or down respectively. Table 4-8B, Mean Time Between Outages—False Positive, and Table 4-8C, Mean Time Between Outages—False Negative, show an example of MTBO depicting a false positive and false negative when considering the reliability of an ILS component.
a)    In Table 4-8B, a very large outage-free Period 5 raises the MTBO on a system which has incurred four outages in the preceding 500 hours of operation. Four outages in 500 hours clearly shows faltering reliability, but the MTBO figure itself shows a system suitable for CAT III RVR 600 operations. If this system has one more outage, the 10,000-hour period would no longer be in the preceding five periods, and the MTBO will drop substantially.
b)    In Table 4-8C, the MTBO is decreased by four short periods caused by four outages over a 300-hour period. However, the system has operated for 3,700 hours without an outage, showing a strong indication that those problems have been repaired and increased system reliability. To get an MTBO of 4,000 hours in Table 4-8C, the system would have to operate for an additional 16,000 hours without an outage (20,000 total hours divided by five outage periods).
3)    Therefore, when Tech Ops informs the appropriate NextGen Branch (AXX-220) of predicted or projected MTBO that do not meet the requirements in Order 6750.24 and may require a downgrade, it is important to discuss the facility’s history, factors which may be affecting MTBO, outages which were attributed to a common cause, repair history, trends affecting the MTBO, and the technician’s confidence in both the repairs and the reliability of the system. When in doubt, the All Weather Operations Specialist (AWOS) should consult AFS-410 before making a decision to downgrade the ILS.

F.    CoS Analyze. Navigation Services created and maintains the CoS Analyze program, which tracks all ILS facilities (LOC and GS) in the United States, including outage history, MTBO, and repair information. CoS Analyze is available to AWOS at http://cos.amc.faa.gov/cos/. CoS Analyze can be used by AFS inspectors to track ILS outages and MTBO for their specific region. The ILS CoS OPRs have usage rights within the CoS Analyze software to mitigate or exclude outages, add comments, and provide updates to system downgrade status. All of this information is available to other users on a read-only basis.

Figure 4-22.  Active Periods Between Outages

Figure 4-22. Active Periods Between Outages

Table 4-8.  Outage Consequences

Lowest ILS Minimum

Fourth Outage

Fifth Outage

Sixth Outage

CAT III RVR 300

CAT III RVR 300 N/A

CAT III N/A

CAT II/III N/A

CAT III RVR 700/600

No effect

CAT III N/A

CAT II/III N/A

CAT II

No effect

No effect

CAT II N/A

Table 4-8A.  Instrument Landing System Reinstatement Periods

Lowest ILS Minimum

Downgraded Minimum Due to System Outages

Outage Free Period to Restore CAT II

Outage Free Period to Restore RVR 700 or 600

Outage Free Period to Restore RVR 300

CAT III RVR 300

CAT I

4 weeks

2 weeks (6 total)

2 weeks (8 total)

CAT III RVR 300

CAT II

N/A

4 weeks

2 weeks (6 total)

CAT III RVR 300

CAT III RVR 700 or 600

N/A

N/A

4 weeks

CAT III RVR 700 or 600

CAT I

4 weeks

2 weeks (6 total)

N/A

CAT III RVR 700 or 600

CAT II

N/A

4 weeks

N/A

CAT II

CAT I

4 weeks

N/A

N/A

Table 4-8B.  Mean Time Between Outages—False Positive

 

Period

Hours

 

Period 1

200

+

Period 2

100

+

Period 3

150

+

Period 4

50

+

Period 5

10000

 

Total Hours =

10500

 

MTBO =

2100

Table 4-8C.  Mean Time Between Outages—False Negative

 

Period

Hours

 

Period 1

3700

+

Period 2

125

+

Period 3

75

+

Period 4

50

+

Period 5

50

 

Total Hours =

4000

 

MTBO =

800

RESERVED. Paragraphs 4-344 through 4-360.