6.7.5.2.6.1 APPENDIX 3 MLS or GLS Introduction Impact Assessment
6.7.5.2.6.2 APPENDIX 3 MLS or GLS Failure Analysis
6.7.5.2.6.3 APPENDIX 3 MLS or GLS Statistical Performance Assessment
6.7.5.2.6.4 APPENDIX 3 MLS or GLS Antenna or Navigation Reference Point Location
6.7.5.2.6.5 APPENDIX 3 MLS or GLS Introduction Flight Testing (as necessary)
6.7.5.2.6.6 APPENDIX 3 MLS or GLS Introduction Documentation 7 APPENDIX 3 APPROACH SYSTEM EVALUATION
7.1 APPENDIX 3 Performance Evaluation
7.2 APPENDIX 3 Safety Assessment 8 APPENDIX 3 AIRBORNE SYSTEM REQUIREMENTS
8.1 APPENDIX 3 General
8.2 APPENDIX 3 Autopilot
8.3 APPENDIX 3 Head Down Guidance
8.4 APPENDIX 3 Head Up Guidance
8.5 APPENDIX 3 Hybrid HUD/Autoland Systems [PoC]
8.6 APPENDIX 3 Satellite Based Approach System
8.7 APPENDIX 3 Reserved
8.8 APPENDIX 3 Autothrottle
8.9 APPENDIX 3 Data link 9 APPENDIX 3 AIRPLANE FLIGHT MANUAL (AFM) APPENDIX 4 WIND MODEL FOR APPROACH SIMULATION APPENDIX 5 OBSTACLE ASSESSMENT FOR RNP FOR CATEGORY I OR CATEGORY II 1 APPENDIX 5 Obstacle Assessment for Standard Required Performance (RNP) Types (e.g., Linear Values of RNP)
1.1 APPENDIX 5 Obstacle Assessment for RNP Approaches and Missed Approaches
1.1.1 APPENDIX 5 General
1.1.2 APPENDIX 5 Final Approach (FAS), Missed Approach (MAS) and other Related Segments
1.1.3 APPENDIX 5 Approach and Missed Approach Conditions To Be Assessed
1.1.4 APPENDIX 5 Touchdown Zone
1.2 APPENDIX 5 Obstacle Criteria
1.2.1 APPENDIX 5 Obstacle Identification Surface Between Point Of Lowest DA(H) and the Runway
1.2.2 APPENDIX 5 Obstacle Identification Surface Between the Point of Lowest DA(H) and a Missed Approach
1.2.3 APPENDIX 5 Obstacle Identification Surface Between the End of the TDZ and a Missed Approach Waypoint
1.2.4 APPENDIX 5 FAS Turn Construction
1.2.4.1 APPENDIX 5 FAS Turn Construction for Fly-by Waypoints
1.2.4.2 APPENDIX 5 FAS Turn Construction for Fly-over Waypoints
1.2.5 APPENDIX 5 MAS Turn Construction
1.2.5.1 APPENDIX 5 MAS Turn Construction for Fly-by Waypoints
1.2.5.2 APPENDIX 5 MAS Turn Construction For Fly-over Waypoints
1.2.6 APPENDIX 5 RNP Reductions
1.2.7 APPENDIX 5 Coordinate Systems
1.2.8 APPENDIX 5 Obstruction and Terrain Charts
1.2.8.1 APPENDIX 5 Recommended Use of USGS Charts
1.2.8.2 APPENDIX 5 Vertical Clearance Adjustments for Certain Topographical Charts
1.2.8.3 APPENDIX 5 Tree Heights
1.2.8.4 APPENDIX 5 Assumptions for Terrain Elevations
1.2.9 APPENDIX 5 Man-Made Obstacle Data
1.2.10 APPENDIX 5 Wheel to Navigation Reference Point or Longitudinal Navigation Reference Points
1.3 APPENDIX 5 Examples of completed RNP Forms 2 APPENDIX 5 FINAL APPROACH OBSTACLE ASSESSMENT - NON-STANDARD LEVELS OF RNP
2.1 APPENDIX 5 Obstacle Assessment For Non-Standard Levels of RNP
2.2 APPENDIX 5 OBSTACLE CRITERIA
2.3 APPENDIX 5 USE OF THESE CRITERIA FOR AIRBORNE SYSTEM AIRWORTHINESS DEMONSTRATIONS WITH
NON-STANDARD LEVELS OF RNP
2.3.1 APPENDIX 5 LATERAL PERFORMANCE
2.3.2 APPENDIX 5 VERTICAL PERFORMANCE
2.4 APPENDIX 5 OTHER CONSIDERTIONS APPENDIX 6 GROUND SYSTEMS AND OBSTACLE CLEARANCE CRITERIA FOR CATEGORY II AND CATEGORY III OPERATIONS 1 APPENDIX 6 PURPOSE 2 APPENDIX 6 GENERAL 3 APPENDIX 6 SUPPORTING NAVIGATION AIDS OR SENSORS FOR CATEGORY II PROCEDURES 4 APPENDIX 6 OBSTACLE CLEARANCE CRITERIA APPENDIX 7 OPERATIONS SPECIFICATIONS 1 APPENDIX 7 General 2 APPENDIX 7 14 CFR Part 121 Operations Specifications - PART A 3 APPENDIX 7 14 CFR Part 121 Operations Specifications - PART C C051 APPENDIX 7 OpSpec C051, Terminal Instrument Procedures C052 APPENDIX 7 OpSpec C052, Basic Instrument Approach Procedure Authorization - All Airports C053 APPENDIX 7 OpSpec C053, Straight-in Category I Approach Procedures other than ILS, MLS, or GPS and IFR Landing Minimums - All Airports C054 APPENDIX 7 OpSpec C054, Limitations and Provisions for Instrument Approach Procedures and IFR Landing Minimums C055 APPENDIX 7 OpSpec C055, Alternate Airport IFR Weather Minimums C056 APPENDIX 7 OpSpec C056, IFR Takeoff Minimums, Part 121 Airplane Operations - All Airports C059 APPENDIX 7 OpSpec C059, Category II Instrument Approach and Landing Operations C061 APPENDIX 7 OpSpec C061, Flight Control Guidance Systems for Automatic Landing Operations Other Than Categories II and III C062 APPENDIX 7 OpSpec C062, Manually Flown Flight Control Guidance System Certified for Landing Operations Other Than Categories II and III C074 APPENDIX 7 OpSpec C074, Straight-in Category I, ILS, MLS, or GLS Approach Procedures and IFR Landing Minimums - All Airports C075 APPENDIX 7 OpSpec C075, Category I IFR Landing Minimums - Circling Maneuvers C076 APPENDIX 7 OpSpec C076, Category I IFR Landing Minimums - Contact Approaches C078 APPENDIX 7 OpSpec C078, IFR Lower Than Standard Takeoff Minimums, 14 CFR Part 121 Airplane Operations - All Airports C090 APPENDIX 7 OpSpec C090, Required Navigation Performance (RNP) APPENDIX 8 USE OF ALTERNATIVE OPERATING MINIMA 1 APPENDIX 8 General 2 APPENDIX 8 Terminology 3 APPENDIX 8 “Go-Around” Transition To A Missed Approach When Using a DA(H) or MDA(H) 4 APPENDIX 8 Alternative RVR/Visibility Value Table 5 APPENDIX 8 Approach and Runway Lighting Systems Definition, Classification, and Equivalence 6 APPENDIX 8 Applicability to Various Classes of Instrument Approach Procedures 7 APPENDIX 8 Transition Provisions 8 APPENDIX 8 Authorized RVR Minima Conversions between “Feet and Meters” 9 APPENDIX 8 Acceptable Meteorological Visibility or RVR Equivalence or Conversion
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1. PURPOSE. This advisory circular (AC) provides an acceptable means, but not the only means, for obtaining and maintaining approval of Category I and II Weather Minima including the installation and approval of associated aircraft systems. This AC is applicable to Title 14 of the Code of Federal Regulations (14 CFR) parts 121, 135, and those part 125 operators not exempted under section 125.1 or not having received an applicable deviation authorization under section 125.3. Certain aspects of this AC are applicable to 14 CFR part 129 operators. Many of the principles, concepts, and procedures described also may apply to 14 CFR part 91 operations and are recommended for use by those operators when applicable.
a. This AC provides some guidance that may be applicable to operations conducted by civil helicopters and powered-lift aircraft. Supplementary guidance for those aircraft may be provided by other FAA or industry documents.
b. Mandatory terms used in this AC such as “shall” or “must” are used only in the sense of insuring applicability of these particular methods of compliance when the acceptable means of compliance described herein is used. This AC does not change, add, or delete regulatory requirements or authorize deviations from regulatory requirements.
c. Major changes introduced in this revision include new provisions for Required Navigation Performance (RNP), Vertical Navigation (VNAV), Flight Management System (FMS), Global Navigation Satellite System (GNSS), Head Up Display (HUD), Global Positioning System (GPS) or GNSS Landing System (GLS), revised obstacle assessment criteria related to RNP, and revised airborne equipment requirements for Category I and II.
d. With issuance of AC120-29A, the former AC 120-29, Criteria for Approving Category I and Category II Landing Minima for FAR 121 Operators, dated December 3, 1974, is canceled.
2. RELATED REFERENCES AND DEFINITIONS.
2.1. Related References.
a. Regulations. 14 CFR part 91, sections 91.175, and 91.189; 14 CFR part 121, sections 121.579, and
121.651; 14 CFR part 125, sections 125.379, and 125.381; 14 CFR part 129, section 129.11; and 14 CFR part 135, section 135.225; 14 CFR part 25, sections 25.1309, and 25.1329.
b. ACs. Current editions of: AC 120-28, Criteria for Approval of Category III Landing Weather Minimal; AC 20-129, Airworthiness Approval of Vertical Navigation (VNAV) Systems for Use In the U.S. NAS and Alaska; AC 20-130, Airworthiness Approval of Navigation or Flight Management Systems Integrating Multiple Navigation Sensors; AC20-138, Airworthiness Approval of GPS Navigation Equipment for use as a Supplemental Navigation System; and AC 25-15, Approval of Flight Management Systems in Transport Category Airplanes.
c. Orders. FAA Orders 8400.8, Procedures for Approval of Facilities for FAR Part 121 and Part 135 CAT III Operations; 8400.10, Air Transportation Operations Inspector’s Handbook; 8400.13, Procedures for the Approval of Category II Operations and Lower Than Standard Category I Operations on Type I Facilities; and 6750.24, Instrument Landing System (ILS) and Ancillary Electronic Component Configuration and Performance Requirements.
d. OpSpecs. Standard Operations Specifications Part A and C.
e. Foreign. Joint Aviation Authority (JAA) ACJ AWO 231, Flight Demonstration (Acceptable Means of Compliance) dated August, 1996.
2.2. Definitions. A comprehensive set of definitions pertinent to Category I and II is included in Appendix I.
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3. BACKGROUND.
3.1. Major Changes Addressed in this Revision. This advisory circular includes additional Category I and Category II criteria or revised Category II criteria for use of Head up Displays, use of Required Navigation Performance (RNP), satellite based navigation, and “engine inoperative” Category II approach procedures. This revision expands information regarding Category I approach procedures, and now includes material pertinent to types of approach procedures other than ILS, MLS, or GLS (e.g., also addresses approaches previously considered as non-precision approaches).
a. This AC also clarifies existing criteria to address frequently asked questions.
b. This revision incorporates changes resulting from the first steps toward international all weather operations (AWO) criteria harmonization taken by the FAA, European JAA, and several other regulatory authorities.
Subsequent revisions of this AC are planned as additional all weather operations harmonization items (AHI(s)) are agreed and completed by FAA and JAA, or internationally.
3.2. Relationship of Operational Authorizations for Category I or Category II and Airborne System Demonstrations. Approach weather minima are approved through applicable operating rules, use of approved instrument procedures and issuance of Operations Specifications (Op-Specs)*. Airworthiness demonstration of aircraft equipment is usually accomplished in support of operational authorizations on a one-time basis at the time of Type Certification (TC) or Supplemental Type Certification (STC). This demonstration is based upon the airworthiness criteria in place at that time. Since operating rules continuously apply over time and may change after airworthiness demonstrations are conducted, or may be updated consistent with safety experience, additional Category I or Category II credit or constraints may apply to Operators or aircraft as necessary for safe operations. In general, criteria related to operational approval is contained in the main body of this AC and criteria related primarily to the airworthiness demonstration of systems or equipment is included in the appendices to this AC.
*NOTE: Operations Specifications are unique Federal Aviation Regulations applicable to a particular operator. OpSpecs are based on the regulations. However, they are specifically applicable to and tailored to a particular operator’s aircraft, routes, and operating circumstances. Standard Operations Specifications are developed by FAA and provided to FAA field offices to aid in development and issuance of the particular and unique OpSpecs issued to each operator.
3.3. Applicable Criteria. Except as described below, new airworthiness demonstrations or operational authorizations should use the criteria of AC 120-29A. Airworthiness demonstrations may use equivalent JAA criteria where agreed by FAA through the FAA/JAA criteria harmonization process. Operators electing to comply with these revised criteria may receive additional credit when using the revised criteria. Aircraft manufacturers or modifiers may elect to demonstrate their aircraft using the revised criteria to seek credit for additional operations.
Aircraft demonstrated using earlier criteria may continue to be approved for Category I or Category II operations in accordance with (IAW) that earlier criteria. Operators seeking additional credit provided for in this AC must, however, use the criteria of this AC for that credit.
3.4. Category I, II, and III Terminology.
a. Since 1985, the FAA has referred to all approaches other than Category II or Category III as Category I, for purposes of regulatory authorization for part 121, 125, 135, and 129 operators (e.g., Operations Specifications).
Thus for consistency and continuity, all Category I approach procedures and operational authorizations are now addressed in this AC. In addition to typical Category I Instrument Landing System (ILS), Microwave Landing System (MLS) and Global Navigation Satellite System (GNSS) Landing System (GLS) procedures (e.g., procedures historically considered as precision approach), information about approaches other than ILS, MLS, and GLS are now included (e.g., procedures historically considered as non-precision approach). The use of the term “non-precision” has been dropped within this AC to reduce confusion which exists with use of this term with current and future
Par 3 Page 3 systems and authorizations, particularly with Vertical Navigation (VNAV) and Area Navigation (RNAV), and with other approaches that may incorporate the use of barometric VNAV to provide a stabilized descent path to a runway.
b. Accordingly, Category I, II, and III terminology used in this AC is based on and is consistent with current U.S. Standard Operations Specifications for part 121, 125, 135, and 129 Operators. Definition usage is also consistent with other ACs (e.g., AC120-28D). Definitions of instrument approach Categories in current use in the U.S. are listed in Appendix 1 of this AC (i.e., Category I, Category II, Category IIIa, IIIb, and IIIc). While there are slight variations of these definitions as used within ICAO and various countries internationally, the broad objectives and practical operational applications are similar. It is significant to note that for U.S. applications to part 121, 125, 135, and 129 operators, Category I is considered to include any instrument approach procedure having minima not less than 200 ft. Height Above Touchdown (HAT) and RVR not less than 1800ft. Accordingly, approaches such as Localizer (LOC); LOC BCRS; Localizer-Type Directional Aid (LDA); Simplified Directional Facility (SDF); Very High Frequency (VHF) Omni-directional Radio Range (VOR); Non-Directional Beacon (NDB); and RNAV are each considered to be Category I approaches. In other states, Category I may only apply to straight-in ILS or MLS instrument procedures. Also, in certain states, lowest authorized minima may be slightly different than as promulgated by the U.S. or ICAO criteria. In a few states, these approach categories relate more closely to aircraft configuration or ILS facilities used, rather than directly landing minima (e.g., Decision Altitude (Height) (DA(H)) and visibility or RVR).
3.5. Requirement for Evaluation Prior to Operations. Instrument approach procedures in the United States and its territories must be validated by an authorized FAA process. Special procedure requests should be made through the CMO to AFS-400.
4. OPERATIONAL CONCEPTS.
4.1. Classification and Applicability of Minima. Landing minima are generally classified by Category I, Category II, and Category III. Definitions for Category I, II, and III are as specified by ICAO and individual states.
For the U.S. these definitions are as included in Appendix 1. Certificate Holding District Offices (CHDO) and Operators should be aware that slight differences exist in definition and use of Category I, II, and III terminology in international operations. Operators should ensure that any differences in definitions do not adversely affect intended operations (see Paragraph 3.4 above).
a. This AC addresses criteria for Category I and Category II instrument approach operations. AC 120-28 addresses takeoff in low visibility conditions and Category III landing operations.
b. Landing minima are generally addressed by parts 91.175, 121.649, 121.651, 121.652 and standard or special OpSpecs Part C. Application of these definitions of Category I, II, and III to landing is discussed in paragraph 4.3.1 below.
c. Although a wide variety of normal and non-normal situations are considered in the design and approval of systems and procedures for Category I and Category II, landing weather minima are primarily intended to apply to normal operations. For non-normal operations, flightcrews are expected to take the safest course of action appropriate for the situation, notwithstanding landing weather minima. When aircraft systems have been demonstrated to account for certain non-normal configurations and a procedure is specified (e.g., an approach with an engine inoperative non-normal procedure), the flightcrew may take account of this information in assessing the safest course of action. In addition, when inoperative aircraft systems have been accounted for in the Airplane Flight Manual (AFM) as an alternate configuration using criteria of this AC (e.g., an approach with an engine inoperative is specified as a demonstrated configuration) operational credit for that configuration (alternate minima credit) may be authorized.
d. Takeoff minimums are generally addressed by parts 91, 121, 135, and standard or special OpSpecs.
Application of takeoff minima is discussed in paragraph 4.2 below.
4.2. Takeoff.
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a. Takeoff Minima.
(1) Takeoff minima are addressed by sections 91.175(f), 121.649, 121.651, 135.225, and standard or special OpSpecs Part C. The authority for lower than standard takeoff minima is contained in sections 135.225(h)(3) and 121.651(a)(1).
(2) OpSpecs are applicable to part 121 and 135 Operators and certain other Operators (e.g., part 125 and part 129). Where minima lower than that provided in standard OpSpecs are necessary, applicable criteria for use of those minima are specified in AC 120-28D. When appropriate, principal operations inspectors (POI(s)) issue OpSpecs specifying the lower minima through paragraph C056 for part 121 Operators and OpSpecs paragraph C057 for part 135 Operators. OpSpecs contain specific guidance regarding pilots, aircraft, and airports when lower than standard takeoff minimums are used.
b. Takeoff RVR Equivalence and Assessment (See also 8.6.3). For takeoff procedures where minima are published only in terms of RVR, but visibility is being reported as a meteorological visibility, tables referenced in Standard OpSpecs may be used to establish equivalent RVR (see Appendix 7, OpSpec Paragraph). This table does not apply to minima published as meteorological visibility being reported as RVR
c. Pilot Assessment of equivalent RVR. For takeoff circumstances where Touchdown Zone RVR is inoperative or is determined by the pilot to be significantly in error (e.g., patchy fog obscuring a transmissometer but not the runway, snow on transmissometer causing erroneous readings), a pilot assessment may be made in lieu of RVR (see Appendix 7, OpSpec Paragraph C078).
(1) To be eligible to use this provision the operator must ensure that each pilot authorized to make this determination has completed approved training addressing pilot procedures to be used for visibility assessment in lieu of RVR, and the pilot can determine the necessary runway markings or runway lighting that must be available to provide an equivalent RVR to that specified to ensure adequate visual reference for the takeoff.
(2) When any pilot assessment of equivalent RVR is made, the pilot must be able to positively determine position on the airport and correct runway, and positively establish that the aircraft is at the correct position for initiation of takeoff. Typically this equivalent RVR assessment is applicable only at a runway threshold where runway identifying markings and number(s) are visible from the takeoff position (e.g., not applicable to intersection takeoffs).
(3) When such a pilot RVR assessment is made, the result of the assessment should typically be provided to any pertinent air traffic facility when practical, and may also be provided to the operator (e.g., dispatch) to facilitate other operations.
4.3. Landing.
4.3.1. Approach and Landing Concepts and Objectives. Landing minima are classified as Category I, Category II, and Category III. Definitions of these categories are provided in Standard OpSpecs Part A paragraph A002, and in Appendix 1. While generally consistent with ICAO definitions, the definitions used in Standard OpSpecs, where different from ICAO, apply and take precedence for U.S. operators, or for international operators conducting operations within the United States, or at U.S. facilities.
a. For U.S. Operators, any instrument approach with a DA(H) or Minimum Descent Altitude (Height) (MDA(H)) and visibility above that specified in OpSpecs for Category I, (see Appendix 7) is considered to be a Category I operation (e.g., an approach with either a DA(H) or an MDA(H) which is not lower than 200 ft. HAT and visibility not less than 1800 RVR is considered to be Category I, even though it may be based on a Navigational Aid (NAVAID) other than ILS).
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b. Any instrument approach with a DA(H) or visibility less than that specified for Category I, but above that specified for Category II, is considered to be a Category II operation.
c. Any instrument approach with a DA(H) less than that specified for Category II (or with no DA(H) or with an Alert Height), or with a visibility less than that specified for Category II, IAW applicable OpSpecs is considered to be a Category III operation.
d. Category I operations may be conducted manually using raw data information, by reference to flight guidance displays (flight directors), or automatically using approved autopilot or autoland systems. However, air carrier operations, particularly with turbine powered aircraft, typically have minima restricted by OpSpecs if a flight director or autopilot is not used.
e. For Category I, basic airworthiness certification for IFR under provisions of 14 CFR part 25 typically is considered an acceptable means of demonstration of capability for operational acceptance of an aircraft and its associated systems. Specific criteria for airworthiness demonstration of certain specific systems or capabilities for Category I are included in Appendix 2 (e.g., FMS or RNP).
f. For Category I minima, it is expected that for non-normal operations (e.g., engine(s) inoperative, hydraulic or electrical system(s) failure) the pilot or operator should consider any necessary adjustment of operating minima, wind limit constraints, or other factors to ensure safe operation with the non-normal condition.
g. Category II operations may be conducted manually using flight guidance (e.g., flight director) displays.
However, most Category II operations are conducted using an autopilot or autoland system, or with combinations of systems using both automatic and flight guidance (e.g., flight director) elements. Additional demonstration or operational assessment beyond that required for basic IFR flight under provisions of basic aircraft 14 CFR part 25 type certification typically is necessary for operational authorization of an aircraft for Category II (see Paragraph 5 and Appendix 3). Specific criteria for airworthiness demonstration of systems or capabilities for Category II are included in Appendix 3 (e.g., for flight director(s), autopilot(s), or HUD) for cases where an applicant seeks prior credit for such a prior airworthiness demonstration documented in the AFM).
h. For Category II minima, certain non-normal conditions are typically considered in the assessment and authorization process. Response to those non-normal conditions may be explicitly defined in the Category II authorization (e.g., engine failure, electrical component failure, or engine inoperative Category II). For failures other than those addressed by the Category II authorization, the pilot or operator may need to adjust the operating minima used, introduce wind limit constraints, or address other factors to ensure safe operation for the particular non-normal condition.
4.3.1.1. Operational Safety Evaluation. For any instrument approach using either Category I or Category II minima, the operator must adequately consider and provide for safe operations considering at least the following:
a. The possibility of a failure of any one of the pertinent navigation systems, flight guidance system, flight instrument system, or annunciation system elements used for the approach or missed approach (e.g., ILS receiver failure, Autopilot disconnect, etc.).
b. The possibility of a failure of a key aircraft component or related supporting system during the approach or missed approach (e.g., engine failure, electrical generator failure, single hydraulic component failure). Even though a particular failure may in itself be considered too remote based on exposure time (e.g., engine failure), it is nonetheless important to address these considerations since, in practical circumstances, a “go-around” may be due to a factor which relates to or leads to the failure, and thus is not an independent event (e.g., flocking bird ingestion).
This is consistent with the long standing principle of safety of operation of multi-engine aircraft in air carrier operations which notes that after passing V1 on takeoff, until touchdown, the aircraft should typically be able to sustain a failure such as engine failure and still safely be able to continue flight and land.
c. The possibility of a balked landing or rejected landing at or below DA(H), or MDA(H), as applicable.
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d. The possibility of loss or significant reduction of visual reference, that may result in or require a go-around.
e. Suitable obstacle clearance following a missed approach, considering applicable aircraft configuration during approach and any configuration changes associated with a go-around (e.g., engine failure, flap retraction).
f. For special airports identified IAW section 121.445 (e.g., mountainous terrain), or other airports with critical obstacles that have not otherwise been accounted for, the ability to ensure suitable obstacle clearance following a rejected landing; applicable aircraft configuration(s) during approach and any configuration changes associated with a go-around and missed approach should be considered.
g. Unusual atmospheric or environmental conditions that could adversely affect the safety of the operation (e.g., extreme cold temperatures, known local atmospheric or weather phenomena that introduce undue risk, etc.).
When conducting a safety assessment of issues listed above, and uncertainty exists as to aircraft failure condition effects, procedural design intent or margins, aircraft characteristics or capabilities following failure, or other such issues, the operator should consult with an appropriate organization source able to provide reliable and comprehensive information. Typically this includes consultation with one or more of the following as applicable, and as necessary:
• Aircraft manufacturer,
• Avionics manufacturer;
• Procedure designer;
• Air Traffic Service provider, or regulatory authority.
NOTE: For definitions and discussion of differences among the terms “balked landing,” “rejected landing,” “go-around,” and “missed approach,” see Appendix 1.
4.3.1.2. Primary and Supplementary Means of Navigation and Required Navigation Performance (RNP).
For the purpose of this AC, “Primary” and “Supplementary” means of navigation and Required Navigation Performance (RNP) are defined in Appendix 1. Application of these terms to instrument approach or takeoff is described below. In addition, it should be noted that the term “Primary Means of Navigation” may apply to either instrument approach initial, intermediate final approach, or missed approach courses of procedures flown to Category I or Category II minima. The term Supplemental Means of Navigation can typically apply to initial or intermediate segments or Missed approach segments, but typically does not apply to flying a final approach course of an instrument procedure. For definitions of Category I or Category II as used by the U.S. and ICAO, see Appendix 1.
a. Primary Means of Navigation. A “Primary Means” of navigation is a means of navigation that satisfies each of the necessary levels of accuracy and integrity for a particular area, route, procedure or operation. The failure of a “Primary Means” of navigation may result in, or require reversion to a “non-normal” means of navigation or alternate level of RNP.
(1) “Availability” as relates to a primary means of navigation is typically addressed in conjunction with the applicable operating rules for use of the system, in the context of the area, airspace, route, procedures, or operations for which system use is intended (e.g., use of multiple versus single sensors or systems, or NAVAID signal access, reliability, or continuity of service as might apply to a particular approach path).
(2) As applicable to instrument approach operations for an air carrier, particularly for a final approach segment or a missed approach segment, the following may be considered to satisfy requirements for a primary means of navigation.
(3) For sensor specific approaches (e.g., VOR, or NDB, or ILS) each particular airborne system using its respective associated NAVAID (e.g., ILS) may be considered as the “primary means of navigation” for completion of that respective specified approach procedure (e.g., ILS RWY 16R).
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(4) When multiple components are required (e.g., ILS, with use of an NDB for the missed approach), the collective set of specified navigation components are considered to be the primary means of navigation for that procedure. Failure of any one of the required components may preclude use of the procedure, or may require reversion to a non-normal means of navigation for completion of the procedure (e.g., failure of the NDB missed approach NAVAID associated with an ILS approach).
(5) For RNAV based procedures where the only method of flying the procedure is by an RNAV or RNAV/RNP system (e.g., FMS), RNAV is considered to be the primary means of navigation for that approach procedure. Any associated NAVAID, or combinations of NAVAIDs, or airborne sensors necessary to achieve the necessary level of FMS performance may be considered as an input sensor(s) to the FMS, but the sensors or NAVAIDs taken alone are not necessarily considered to be the primary means of navigation.
(6) Where RNAV systems are used to overfly other types of instrument approach procedures (e.g., FMS RNAV systems over-flying VOR or NDB procedures), the RNAV system may be considered as a supplemental system if the aircraft can revert to use of the underlying procedure flown with “raw data,” in the event of failure of the RNAV system (see b. below).
b. Supplementary Means of Navigation. A “Supplementary Means” of navigation is a means of navigation which satisfies one or more, but not necessarily all of the necessary levels of accuracy, integrity, and availability for a particular area, route, procedure, or operation. The failure of a “Supplementary Means” of navigation may result in, or require reversion to another alternate “normal” means of navigation for the intended route, procedure, or operation.
(1) As applicable to instrument approach operations for an air carrier, particularly for a final approach segment or a missed approach segment, the following may be considered to satisfy requirements as a supplementary means of navigation.
(2) When procedures have multiple methods to achieve compliance (e.g., a multi-sensor FMS over-flying a VOR approach, or an ILS approach with the choice of either an NDB or a VOR-based missed approach), those airborne systems which have another alternate normal means to accomplish the procedure, or a portion of the procedure, for one or more applicable segments, may be considered as supplementary for those applicable segments
(e.g., if the FMS should fail, and the crew is monitoring the underlying VOR information, and the crew can transition to use of VOR-based navigation) the FMS may be considered as supplementary.
(3) Or, if, after an ILS approach, FMS RNAV capability is used to overfly a VOR/DME-based missed approach (with VOR/ DME NAVAID facilities operating), the FMS RNAV capability may be considered supplementary. Note, however, that if the specified approach/missed approach VOR/DME NAVAIDs are not operative, and the FMS RNAV operation is based on use of multi-sensor NAVAID capability, then the FMS use for that approach/missed approach would typically be considered a primary means of navigation.
c. Required Navigation Performance (RNP). Required Navigation Performance is a statement of the navigation performance necessary for operation within a defined airspace (Adapted from ICAO - IS&RP Annex 6).
Required Navigation Performance is specified in terms of accuracy, integrity, and availability of navigation signals and equipment for a particular airspace, route, procedure, or operation.
4.3.1.3. Use of ICAO Standard NAVAIDs. U.S. Category I or Category II Operations are based on use of ICAO standard NAVAIDs, equivalent NAVAIDs, or other NAVAIDs acceptable to FAA and approved in OpSpecs.
Authorization for use of NAVAIDs other than ICAO Standard NAVAIDs must be coordinated with AFS-400.
In the context of this AC, a Standard Landing Aid (SLA) is considered to be any navigation service or navigation aid provided by a State which meets internationally accepted performance standards (e.g., ICAO Standards and Recommended Practices (SARPs), or equivalent U.S. or other State standards - see Appendix 1).
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4.3.1.4. Standard Instrument Approach Procedures (SIAPS).
a. Acceptable Instrument Approach Procedure Basis. Instrument approach procedures used by Operators IAW with this AC should be based on:
(1) U.S. Standard Instrument Approach Procedures;
(2) For non-U.S. airports, foreign instrument approach procedures acceptable to FAA promulgated by the state of the airport of landing (i.e., ICAO - State of the Aerodrome). The operator may propose use of such procedures for Principal Operations Inspector (POI), Aircrew Program Manager (APM), or Certificate Management Office (CMO) acceptance;
(3) Military instrument procedures acceptable to FAA for operations at military facilities. The operator may propose use of such procedures for POI, APM, or CMO acceptance;
(4) Special instrument approach procedures approved by the FAA;
(5) Special instrument approach procedures developed by the operator which are acceptable to FAA, or procedures developed by the operator using methods acceptable to FAA; or
(6) Special instrument approach procedures, acceptable to FAA, developed by other U.S. or non-U.S.
Operators, or by the State of the Aerodrome (for foreign airports).
b. Considerations for use of procedures other than U.S. Standard procedures. For procedures other than those developed IAW FAA Order 8260.3, United States Standards for Terminal Instrument Procedures (TERPS), the operator must ensure consideration of at least the following factors related to use of those instrument procedures:
(1) Availability of suitable weather reporting and forecasts;
(2) Identification of any necessary alternate airports or alternate minima;
(3) Ability to discontinue an approach, if necessary, from any point to touchdown;
(4) Suitability of the airborne equipment to use the procedure (e.g., compatibility of the airborne equipment with the type/characteristics of the ILS, VOR, DME, NDB ground facilities used);
(5) Suitability of Ground Systems/Equipment (e.g., lighting, transmissometers, pilot control of lighting);
(6) Suitability of NAVAIDs (e.g., maintenance, monitoring);
(7) Suitability of Airport/Runway (e.g., obstructions, clear zones, markings);
(8) Availability of Aeronautical Information (e.g., timely NOTAM availability);
(9) Identification of any special Training or qualification related to the procedure; and
(10) Resolution of any issues identified from adverse “service experience” with the procedure.
c. Special Instrument Approach Procedures. Special instrument approach procedures should be coordinated with the Flight Standards Division of the FAA region having responsibility for the airport of the procedure. Special procedures should address any provisions associated with application of section 121.445 for special airport qualification. Special procedures are approved by AFS-400 and issued by the POI after coordination with pertinent FAA organizations.
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d. Use of FAA/JAA Harmonized Instrument Approach Minima Tables. Information from FAA/JAA harmonized instrument approach minima tables are provided in Appendix 8. Unless otherwise authorized by AFS-400, procedures incorporating these minima are issued as special instrument procedures through OpSpecs, or through a Letter of Authorization (LOA). Minima based on values provided in Appendix 8 should not be below the lowest minima authorized through a Category I Standard OpSpec authorization, or below any applicable published foreign aerodrome minima when operating outside the United States (see Paragraph 6.2.18 and Appendix 8).
4.3.1.5. “Steep Approaches” and Approach Path Descent Angle Constraints. Approach path angles between
2.75 degrees and 3.77 degrees are considered standard for air carrier operations. Approach angles above 3.77 degrees are considered “steep angle” and, if authorized, may require additional assessment. Air carrier use of approach angles over 3.77 degrees requires coordination with AFS-400. Use of approach angles over 4.5 degrees should normally be based on an associated aircraft type AFM provision for “steep angle approaches,” IAW AC 25-7A, Flight Test Guide for Certification of Transport Category Airplanes, or equivalent, and paragraph 6.8 of Appendix 2.
4.3.1.6. “Normal Maneuvering” Considerations. Part 91, section 91.175 requires that approach procedures should be based on use of “normal maneuvers” before and after passing DA(H) or MDA(H). Normal maneuvers typically do not involve use of bank angles greater than 30 degrees, pitch attitudes in excess of 25 degrees nose up or 10 degrees nose down, or sink rates in excess of 1100 ft. per minute below 500 ft. HAT while maneuvering to land within the touchdown zone, during go-around, or during a rejected landing. During a missed approach, pitch attitudes in excess of +30 degrees or bank angles greater than 30 degrees would typically be considered excessive.
4.3.1.7. Non-Normal Events or Configurations. Takeoff and landing weather minimums are intended for normal operations. When non-normal events occur, flightcrews are expected to take the safest course of action to ensure safe completion of the flight. Using emergency authority, crews may deviate from rules or polices, to the extent necessary for the circumstances, to minimize risk during landing.
Paragraph 6.1.8 addresses guidelines and procedures to be considered in conducting an instrument approach during a non-normal event.
4.3.1.8. Go-Around Safety.
a. General. A multiengine aircraft conducting a Category I or Category II instrument approach should be capable of safely executing a “one-engine-inoperative” go-around from any point in an approach prior to touchdown with the aircraft in a normal configuration, or specified non-normal configurations (e.g., engine out, if applicable).
This is necessary to provide for go-around safety due to missed approaches or rejected landings due to a variety of circumstances such as:
• Unexpected environmental conditions (e.g., cross winds, turbulence)
• Aircraft related failures (e.g., gear unsafe)
• Air Traffic Service contingencies (e.g., RTO on a crossing runway)
• Loss of visual reference
• When a pilot finds the runway surface unsuitable (e.g., clutter, flocking birds)
• When the runway is blocked (airport vehicles or exiting aircraft ahead not clear), or due to a go-around or missed approach due to any other reason
(1) This objective may be achieved by the operator providing information to flightcrews on an appropriate lateral flight path to follow to enable the aircraft to safely operate to the runway, and out from the runway following a rejected landing. In the rare event that operation out of a runway may not be possible following a rejected landing, then provision of suitable information on a “commit point,” or equivalent condition (e.g., limit weight, minimum speed, or suitable configuration) may instead be provided. The intent of providing information on safe go-around capability is to identify the best option or options for a safe lateral ground track and flight path to follow in the event that a missed approach, balked landing, rejected landing or go-around is necessary. It is not the intention of this provision to require or indicate the need for an analysis of each flight, or a dispatch assessment, or an individual
Page 10 Par 4 flight landing weight assessment or limitation. Operators may make the judgment as to whether a review on a “perflight” or specific condition basis may or may not be needed.
(2) While coping with the go-around contingency situation is appropriate for any operation, it is particularly important for low visibility operations in which the pilot has minimum time to respond, and may have limited visual reference available to safely cope with the adverse condition (e.g., night and poor visibility). Further, “go-around” safety should be addressed regardless of when an engine failure may occur prior to landing. However, operators may elect to distinguish between procedures or expected crew response for engine failures occurring at various times during a flight as follows:
(a) Engine failure occurring enroute or prior to passing a final approach fix or point,
(b) Engine failure during a final approach segment, or
(c) Engine failure after passing DA(H) or after descending below MDA(H) but prior to touchdown, or during a go-around or missed approach.
(3) For an engine failure occurring prior to final approach, flight diversion planning should allow for the potential need for a missed approach or balked landing, and for the need to maintain subsequent suitable obstacle clearance (e.g., when making suitable diversion choices - sections 121.161, 121.191, or 121.193. The pilot should consider any adjustment to minima, procedures or missed approach path that may be appropriate to facilitate safe obstacle clearance (e.g., following a suitable operator-developed takeoff procedure, published takeoff procedure, or IFR Departure Procedure (DP)). This is particularly appropriate if U.S. TERPS or ICAO PANS-Ops-specified instrument procedural gradients cannot be met during any portion of a go-around or missed approach, or if following a suitable lateral path cannot be ensured (e.g., crosswinds with no course guidance available, cannot maintain VMC, or at night).
(4) For engine failure during approach, if there is any doubt of the ability to safely complete the landing or ensure a safe balked landing and missed approach capability, the pilot should consider the advisability of discontinuing the approach and diverting to a different airport or runway, to better ensure safe missed approach or balked landing obstacle clearance.
(5) For engine failure after passing DA(H) or descending below MDA(H), the pilot should be prepared to expeditiously follow or join any pre-established and applicable “T-procedure” or “IFR Departure Procedure,” or equivalent, until becoming established on a published segment of the missed approach procedure, at or above a safe altitude.
(6) Accordingly, an operator should have reviewed the missed approach and rejected landing flight path to ensure that in the event of a go-around the aircraft is able to ensure safe obstacle clearance following a missed approach or go-around. This can be particularly important in mountainous areas where the landing runway may be in a direction not typically used for takeoff (e.g., an airport that is one way in, and the opposite direction out).
b. Go-Around Assessment Considerations.
(1) Operators may accomplish such assessments generically for a particular runway, procedure, aircraft type, and expected performance, and need not perform this assessment for each specific flight. Operators may use simplifying assumptions to account for the transition, reconfiguration, and acceleration distances following goaround (e.g., use expected landing weights, assume anticipated landing flap settings).
(2) The operational considerations should include:
(a) Go-around configuration transitions from approach to missed approach configuration including expected flap settings and flap retraction procedures.