Appendix 2 Page 19 (and 20)
a. The integrity of the datalink should be commensurate with the integrity required for the approach.
b. The role of the datalink in the approach system must be addressed as part of the aircraft system certification process until such time as an acceptable national or international standard for the ground system is established.
9. AIRPLANE FLIGHT MANUAL (AFM). The AFM should contain the following information:
a. Any conditions or constraints on approach performance with regard to airport conditions (e.g., elevation, ambient temperature, approach path slope, runway slope and ground profile under the approach path).
b. The criteria used for the demonstration of the system, acceptable normal and non-normal procedures, the demonstrated configurations and types of facilities used, and any constraints or limitations necessary for safe operation.
c. The type of navigation facilities used as a basis for certification. This should not be taken as a limitation on the use of other facilities. The AFM may contain a statement regarding the type of facilities or condition known to be unacceptable for use.
d. Information should be provided to the flightcrew regarding atmospheric conditions under which the system was demonstrated (e.g., headwind, crosswind, tailwind etc.). The AFM should contain a statement that “Credit may not be predicated on the use of <type of system> if conditions exceed … (those for which the system received airworthiness approval).”
e. Any necessary performance, procedure, or configuration data to permit an operator to determine climb gradient and transition distances for safe obstacle clearance during a missed approach, balked landing, or rejected landing. Note that this information need not be specifically included in the AFM if it is available to the operator using some other method acceptable to the operator and manufacturer (e.g., FCOM, supplementary performance information, separate AFM appendix).
Data may be based on corresponding takeoff performance and obstacle assessment data if appropriate accommodation of configuration change and transition distance can be accounted for. Otherwise, additional information on data that may be useful to an operator for determination of engine-inoperative missed performance, maximum allowable weight, or obstacle assessments is discussed in the main body of this advisory circular in Paragraph 4.3.1.8.
NOTE 1: The AFM limitation section should not specify DA(H) or RVR limitations.
NOTE 2: Section 2 of AC 25.1581-1 discusses AFM contents. The approval status referenced in 2 b
(9) (vii) for Category I, II, or III of that AC should be noted in the Normal Procedures Section of the AFM, in accordance with the above provisions of 9. Airplane Flight Manual.
Appendix 3 APPENDIX 3. AIRBORNE SYSTEMS FOR CATEGORY II Mandatory terms used in this Advisory Circular (AC) such as “shall” or “must” are used only in the sense of ensuring applicability of these particular methods of compliance when the acceptable means of compliance described herein are used. This AC does not change, add, or delete regulatory requirements or authorize deviations from regulatory requirements.
1. PURPOSE. This appendix contains airworthiness criteria for the approval of aircraft equipment and installations required to conduct an approach in Category II weather minima.
2. GENERAL.
The type certification approval for the equipment, system installations, and test methods should be based on a consideration of factors such as the intended function of the installed system, its accuracy, reliability, and fail-safe features, as well as the operational concepts contained in the body of this AC. The guidelines and procedures contained herein are considered acceptable methods of determining transport category airplane airworthiness to conduct an approach in Category II weather conditions.
The overall assurance of performance and safety of an operation can only be assessed when all elements of the system are considered. This appendix includes a discussion of the non-aircraft elements of a system so that an overall assessment of the operation can be accomplished.
References to Joint Airworthiness Authority (JAA) All Weather Operations Regulations (JAR) are provided to facilitate the All Weather Operations Harmonization process. A reference to a JAR provision does not necessarily mean that the FAA and JAA requirements are equivalent but that they are related with similar intent. The FAA may typically identify which JAR provisions are acceptable to FAA at the time a type certification basis is established.
3. INTRODUCTION. This appendix addresses the approach phase of flight. For the purpose of this appendix, the approach phase of flight is defined as the flight segment from the Final Approach Fix (FAF) to the Category II decision height. This appendix provides criteria which represents an acceptable means of compliance with performance, integrity, and availability requirements for low visibility approach. An applicant may propose alternative criteria. With new emerging technologies, there is a potential for many ways of conducting low visibility approach operations. This appendix does not attempt to provide criteria for each potential combination of airplane and non-airplane elements.
a. Operations using current ILS or MLS ground-based facilities and airplane elements are in use, and the certification criteria for approval of these airplane systems are established. Other operations, using non-ground based facilities or evolving ground facilities (e.g., local area augmented Global Navigation Satellite System (GNSS)), and the use of some new aircraft equipment require Proof of Concept testing to establish appropriate criteria for operational approval and system certification. The need for a Proof of Concept program is identified in this AC with a [PoC] designator. This appendix provides some general guidelines, but not comprehensive criteria, for airplane systems that require a Proof of Concept.
b. The intended flight path may be established in a number of ways. For systems addressed by this appendix, the reference path may be established by a navigation aid (e.g., ILS, MLS). Other methods may be acceptable if shown feasible by a Proof of Concept [PoC]. Methods requiring PoC include, but are not limited to:
• the use of ground surveyed waypoints, either stored in an on-board data base or provided by data link to the airplane, with path definition by the airborne system
• sensing of the runway environment (e.g., surface, lighting, and/or markings) with a vision enhancement system
Appendix 3 On-board navigation systems may have various sensor elements by which to determine airplane position. The sensor elements may include ILS, MLS, GNSS with ground-based augmentation (GLS), or inertial information. Each of these sensor elements should be used within appropriate limitations with regard to accuracy, integrity, and availability.
Indications of the airplane position with respect to the intended path can be provided to the pilot in a number of ways.
• deviation displays with reference to navigation source (e.g., Instrument Landing System (ILS) receiver, Microwave Landing System (MLS) receiver), or
• on-board navigation system computations with corresponding displays of position and reference path, or
• by a vision enhancement system. [PoC]
c. The minimum visibility required for safe operations with such systems and backup means will be specified by FAA Flight Standards in the operational authorization.
4. TYPES OF APPROACH OPERATIONS. The airworthiness criteria in this appendix are intended to be consistent with the operational concepts of Paragraph 4.3 of the main body of this AC.
4.1. Operations based on a Standard Landing Aid.
ILS and MLS have been characterized by appropriate International Civil Aviation Organization l (ICAO) standards, and for the purpose of certification in accordance with this Appendix may be considered a Standard Landing Aid.
Landing Systems based on GNSS Landing System (GLS) may use interim United States criteria, or other FAA agreed State criteria, or other international standards developed for acceptable combination of space and ground-based elements. Acceptable overall aircraft performance may be established based upon the assumption that these services are used and maintained to the specified standards identified, or as specified in the applicable airworthiness approval.
4.2. Operations based on Required Navigation Performance (RNP). The airworthiness criteria in this appendix support the operational concept for RNP as described in Paragraph 4.5 in the main body of this AC.
4.2.1. Standard RNP Types. Approach operations may be specified based upon standard RNP type designations.
The type designation identifies the performance standard required to conduct the operation. The RNP Type will have a lateral performance component and may additionally have a vertical component. Refer to Paragraph 4.5.1 in the main body of this AC for Standard RNP Types.
4.2.2. Non-standard RNP Types. Some operations may be approved for Non-Standard RNP Types - Refer to Paragraph 4.5.2 in the main body of this AC. It is envisioned that the airplane systems approval process for Non- Standard RNP Types will be equivalent to that used for Standard RNP Types unless otherwise agreed with the FAA.
5. TYPES OF APPROACH NAVIGATION SERVICE.
5.1. ILS.
The ILS is supported by established international standards for ground station operation. These standards should be used in demonstrating airplane system operation.
The airplane system response during a switchover from an active localizer transmitter to a backup transmitter shall be established.
Appendix 3 The Airplane Flight Manual shall indicate that operation is predicated upon the use of an ILS facility with performance and integrity equivalent to, or better than, an International Civil Aviation Organization (ICAO) Annex 10 Facility Performance Category II ILS, an U.S. Type II or equivalent.
5.1.1. ILS Flight Path Definition. The required lateral and vertical flight path is inherent in the design of the ILS.
Acceptable performance and integrity standards have been established for ILS.
5.1.2. ILS Airplane Position Determination. The airplane lateral and vertical position relative to the desired flight path is accomplished by an airplane ILS receiver that provides deviation from the extended runway centerline path when in the coverage area.
5.2. MLS.
The MLS is supported by established ICAO Annex 10 international standards for ground station operation. These standards should be used in demonstrating airplane system operation.
The airplane system response during a switchover from an active azimuth transmitter to a backup transmitter shall be established.
The Airplane Flight Manual (AFM) shall indicate that operation is predicated upon the use of an MLS facility with performance and integrity equivalent to, or better than, an ICAO Annex 10 Facility Performance Category II MLS, or equivalent.
5.2.1. MLS Flight Path Definition. The lateral and vertical required flight path is inherent in the design of the MLS. Acceptable performance and integrity standards have been established for MLS.
5.2.2. MLS Airplane Position Determination. The airplane lateral and vertical position relative to the desired flight path is accomplished by an airplane MLS receiver that provides deviation from the extended runway centerline path when in the coverage area.
5.3. GNSS Landing System (GLS) [PoC].
This appendix section is not intended to provide a comprehensive means of compliance for airworthiness approval of GNSS-based systems. Currently approved systems are ILS or MLS-based. The application of new technologies and systems will require an overall assessment of the integration of the airplane components with other elements (e.g., new ground-based aids, satellite systems, advanced radar mapping systems, enhanced vision sensor systems) to ensure that the overall safety of the use of these systems for Category II. This GNSS section is included to identify important differences between conventional ILS/MLS-based systems and GNSS based systems that affect GLS criteria development.
The performance, integrity and availability of any ground station elements, any data links to the airplane, any satellite elements and any data base considerations, when combined with the performance, integrity, and availability of the airplane system, should be at least equivalent to the overall performance, integrity, and availability provided by ILS to support Category II operations.
5.3.1. GLS Flight Path Definition. Appropriate specification of the required flight path for approach, or approach, landing, and rollout (as applicable), is necessary to assure safety of the operation to the relevant operational minima.
The required flight path should be established to provide adequate clearance between the airplane and fixed obstacles on the ground, between airplanes on adjacent approaches, and to ensure that the airplane stays within the confines of the runway.
a. The effect of the navigation reference point on the airplane flight path and wheel to threshold crossing height must be addressed.
Appendix 3
b. The required flight path is not inherent in the design of a GNSS-based approach, landing, and rollout system;
therefore, an airplane navigation system must specify a sequence of earth-referenced path points, or the airplane must receive information from a ground-based system, to define the approach, landing, and rollout required path points.
c. Certain path points, waypoints, leg types, and other criteria are necessary to safely implement the approach, or approach, landing, and rollout operations based on satellite and other integrated multi-sensor navigation systems.
d. Figure 4.6-1 in the main body of this AC shows the minimum set of path points, waypoints, and leg types considered necessary to specify the flight path for approach, or approach, landing, and rollout operations.
e. The required flight path may be stored in an airplane database for recall and use by the command guidance and/or control system when required to conduct the approach to relevant minima for landing and rollout.
f. The definition, resolution, and maintenance of the waypoints which define the required flight path and flight segments is key to the integrity of this type of approach, landing, and rollout operation.
g. A mechanism should be established to assure the continued integrity of the flight path designators.
h. The integrity of any database used to define required path points for an approach should be addressed as part of the certification process. The flightcrew shall not be able to modify information in the database that relates to the definition of the required flight path for the final approach, and if necessary, initial missed approach.
5.3.2. GLS Airplane Position Determination. The safety of an approach operation is, in part, predicated on knowing where the airplane is positioned relative to the required flight path. Navigation satellite systems exist which can provide position information to specified levels of accuracy, integrity, and availability. The accuracy, integrity, and availability can be enhanced by additional space and ground-based elements. These systems provide certain levels of capability to support present low visibility operations and are planned to have additional future capability.
a. Satellite systems have the potential to provide positioning information necessary to guide the airplane during approach. If operational credit is sought for these operations, the performance, integrity, and availability must be established to support that operation. Ground-based aids such as differential position receivers, pseudolites, etc., and a data link to the airplane may be required to achieve the accuracy, integrity, or availability for certain types of operation.
b. A level of safety equivalent to current ILS-based operations should be established.
c. The role of the satellite-based elements in the landing system should be addressed as part of the airplane system certification process until such time as acceptable national or international standards for satellite-based systems are established.
Basic GNSS (Un-augmented). This is the basic navigation service provided by a satellite system. No additional navigation service elements are used to enhance accuracy or integrity of the operation.
Differential Augmentation. The role of the differential station in the landing system should be addressed as part of the airplane system certification process, unless an acceptable national or international standard for the ground reference system is established.
Local Area Differential Augmentation. Local Area Differential (LAD) augmentation consists of a set of ground-based GNSS receivers that are used to derive pseudo-range corrections and integrity data referenced to a point on or near the airport. This augmentation data is then provided to the airplane via a local, ground-based data broadcast signal.
Appendix 3 Wide Area Differential Augmentation. Wide Area Differential (WAD) augmentation may be used to provide approach capability supporting appropriate levels of Category II procedures.
Typically only LAD systems provide a basis for establishing the necessary position fixing accuracy, integrity, and availability for the final portion of a final approach segment or rollout. Unaugmented GNSS or WAD are typically only suited for support of initial or intermediate segments of an approach, final approach to restricted DA(H)s, or missed approach. GNSS or WAD may, however, be used in conjunction with Category II procedures for applications such as equivalent DME distance, or marker beacon position determination, when authorized by the operating rules.
5.3.3. Data Link [PoC]. A data link may be used to provide data to the airplane to provide the accuracy necessary to support certain operations (e.g., navigation waypoints, differential corrections for GNSS).
a. The integrity of the data link should be commensurate with the integrity required for the operation.
b. The role of the data link in the approach, or approach and landing system should be addressed as part of the airplane system certification process unless an identified acceptable U.S. or international standard(s) for the data link ground system is applicable and is used.
6. BASIC AIRWORTHINESS REQUIREMENTS. This section identifies airworthiness requirements, including those for performance, integrity, and availability that apply to all types of airplane systems, independent of the type of approach and landing or navigation system used. The definitions of performance, integrity, and availability are found in Appendix 1. The basic airworthiness criteria are intended to be independent of the specific implementation in the airplane or the type of approach system being used. Criteria may be expanded further in later sections of this appendix as it applies to a particular airplane system or architecture.
Note: Continuity of Approach Function may involve aircraft systems, ground systems and, in some cases, space based systems. This AC addresses the aircraft part of the system, and aircraft criteria will be defined in terms of aircraft system availability to provide quantifiable criteria for airworthiness compliance.
6.1. General Requirements. An applicant shall provide a certification plan which describes how any non-aircraft elements of the Approach System relate to the aircraft system from a performance, integrity, and availability perspective. Standard Landing Aids (SLA) can be addressed by reference to ICAO Standards and Recommended Practices (SARPS).
a. The plan for certification shall describe the system concepts and operational philosophy to allow the regulatory authority to determine whether criteria and requirements other than those contained in this appendix are necessary.
b. The approach system performance should be established considering the environmental and deterministic effects that may reasonably be experienced for the type of operation for which certification and operational approval will be sought.
c. Where reliance is placed on the pilot to detect a failure of engagement of a mode when it is selected (e.g., goaround), an appropriate indication or warning must be provided.
d. The effect of the failures of the navigation facilities must be considered taking into account ICAO and other pertinent State criteria.
e. The effect of the aircraft navigation reference point on the airplane flight path and wheel-to-threshold crossing height shall be assessed.
Appendix 3
6.2. Approach System Accuracy Requirements. The following items are general criteria that apply to the various types of approach operation.
a. Performance shall be demonstrated by flight test, or analysis validated by flight test, using at least 3 different representative facilities for a minimum of 20 total approaches, with a representative range of environmental and system variables which have an effect on overall performance.
b. The performance assessment shall take into account at least the following variables with the variables being applied based upon their expected distribution:
(1) Configurations of the airplane (e.g., flap settings);
(2) Center of gravity;
(3) Landing weight;
(4) Conditions of wind, turbulence, and wind shear;
(5) Characteristics of ground and space based systems and aids (i.e., ILS, MLS, GLS); and
(6) Any other parameter which may affect system performance (e.g., airport altitude, approach path slope, variations in approach speed).
c. The criteria for acceptable approach performance are based upon acquiring and tracking the required flight path to the appropriate minimum altitude for the procedure. The acquisition should be accomplished in a manner compatible with instrument procedure requirements and flightcrew requirements for the type of approach being conducted.
d. An approach guidance system shall not generate command information (e.g., flight director, HUD etc.) which results in flight path control that is oscillatory or requires unusual effort by the pilot to satisfy the performance requirements.
e. An approach control system shall not generate flight path control (e.g., autopilot) with sustained oscillations.
f. The approach system must cause no sustained nuisance oscillations or undue attitude changes or control activity as a result of configuration or power changes or any other disturbance to be expected in normal operation.
6.2.1. ILS. The performance standards for signal alignment and quality contained in ICAO Annex 10, or an equivalent State standard, are acceptable standards for operations based on ILS. These standards shall be used in establishing the performance of the operation.
a. Lateral tracking performance from 300 ft. HAT to 100 ft. HAT should be stable without large deviations (i.e., within ±25 microamps deviation) from the indicated course, for 95% of the time per approach.
b. Vertical tracking performance from 300 ft. HAT to 100 ft. HAT should be stable without large deviations
(i.e., within ±35 microamps deviation) from the indicated path or ±12 ft, whichever is greater, for 95% of the time per approach.
Note: When this provision is applied to path tracking in conjunction with Category III, momentary excursions up to ±75 microamps during test demonstrations may be acceptable if flight guidance system touchdown and landing performance is otherwise shown to be satisfactory.
Appendix 3
c. The Continuous Method and the Pass/Fail methods found in JAR ACJ AWO 231 may be used in lieu of the 95% of the time per approach and the minimum number of 20 approaches stated above.
6.2.2. MLS. The performance standards for signal alignment and quality contained in ICAO Annex 10 or an equivalent State standard are acceptable standards for operations based on MLS. These standards shall be used in establishing the performance of the operation.
a. Lateral tracking performance from 300 ft. HAT to 100 ft. HAT should be stable without large deviations (i.e., within ±25 microamps deviation) from the indicated course, for 95% of the time per approach.
b. Vertical tracking performance from 300 ft. HAT to 100 ft. HAT should be stable without large deviations
(i.e., within ±35 microamps deviation) from the indicated path or ±12 ft, whichever is greater, for 95% of the time per approach.
Note: When this provision is applied to path tracking in conjunction with Category III, momentary excursions up to ±75 microamps during test demonstrations may be acceptable if flight guidance system touchdown and landing performance is otherwise shown to be satisfactory.
c. The Continuous Method and the Pass/Fail methods found in JAR ACJ AWO 231 may be used in lieu of the 95% of the time per approach and the minimum number of 20 approaches stated above.
6.2.3. GLS [PoC]. Paragraph 5.3 provides background GLS considerations.
a. Lateral tracking performance from 300 ft. HAT to 100 ft. HAT should be stable without large deviations (i.e., within ±25 microamps deviation) from the indicated course or path, or equivalent, for 95% of the time per approach.
b. Vertical tracking performance from 300 ft. HAT to 100 ft. HAT should be stable without large deviations
(i.e., within ±35 microamps deviation) from the indicated path or ±12 ft, whichever is greater, or equivalent, for 95% of the time per approach.
Note: When this provision is applied to path tracking in conjunction with Category III, momentary excursions up to ±75 microamps during test demonstrations may be acceptable if flight guidance system touchdown and landing performance is otherwise shown to be satisfactory.
c. The Continuous Method and the Pass/Fail methods found in JAR ACJ AWO 231 may be used in lieu of the 95% of the time per approach and the minimum number of 20 approaches stated above.
6.2.4. RNP. The accuracy criteria for RNP are designed to enable a seamless transition from en route RNP to approach RNP to be accomplished. RNP operations are based upon the accuracy of the airplane flight path in absolute terms with respect to the defined flight path over the ground. The Total System Error (TSE) will be characterized by the combined performance of airplane systems and any navigation aids. The certification plan should identify any navigation aid(s) on which the RNP performance will be established and how the airplane performance interacts with the navigation aid(s) to meet the TSE performance requirements. The certification plan should identify the assumed relationship between airplane performance and any navigation aid performance.
a. The approach RNP is specified from the FAF to the point along the final approach segment at which the lowest applicable Decision Altitude (Height) (DA(H)) typically is applied. There may be one or more levels of RNP specified on a final segment. Missed approach RNP, or levels of RNP if more than one level or RNP is specified, is typically specified from a point related to the lowest applicable DA(H), and typically continues to a missed approach holding fix or missed approach waypoint. RNP also may be applied to a “go-around safety” assessment. When applied to a “go-around safety assessment” the RNP level and associated obstacle clearance start at the end of the touchdown zone with an expanding lateral area that widens to match the level of RNP used, and then continues at the
Appendix 3 RNP level(s) specified. The expanding lateral area starts on the centerline for the approach at the end of the touchdown zone and widens at a 7.5 degree splay, or ICAO 1:8 splay, depending on procedure development criteria used. It is applicable from the end of a touchdown zone to reaching the missed approach holding fix or applicable missed approach waypoint (See Appendix 5).
b. Assumptions regarding the performance for any radio navigation aid(s) used should be consistent with ICAO Annex 10 or an equivalent State standard. In cases where site specific geometry must be considered in the evaluation of the NSE, limits on the assumed geometry should be identified.
c. The guidance or control system shall be demonstrated to maintain a flight path which tracks the defined flight path to the RNP Type as specified in Paragraph 4.5 of the body of this AC, as applicable.
6.2.5. Flight Path Definition. Refer to Paragraph 4.6 in the main body of this AC for consideration on Flight Path Definition when navigation aids are used which do not have the required flight path inherent in the structure of the signal in space.
6.3. Approach System Integrity Requirements. The applicant shall provide the certification authority with an overall operational safety assessment plan for the use of systems other than ILS or MLS for “path in space” guidance.
This plan shall identify the assumptions and considerations for the non-aircraft elements of the system and how these assumptions and considerations relate to the airplane system certification plan.
a. The onboard components of the landing system, considered separately and in relation to other associated onboard systems, should be designed to comply with Title 14 of the Code of Federal Regulations (14 CFR) part 25, section 25.1309, considering any specific safety related criteria identified in this appendix, or as identified in accordance with the operating rules.
b. The following criteria is provided as advisory material for the application of section 25.1309 to Landing Systems:
6.3.1. ILS. The aircraft system response to loss of ILS guidance signals (localizer and glideslope) shall be established.
The aircraft system response during a switchover from an active localizer or glideslope transmitter to a backup transmitter shall be established.
6.3.2. MLS. The aircraft system response to loss of MLS guidance signals (elevation and azimuth) shall be established.
The aircraft system response during a switchover from an active elevation or azimuth transmitter to a backup transmitter shall be established.
6.3.3. GLS. The aircraft system response to loss of GLS guidance signals shall be established.
The aircraft system response during any switchover to alternate differential augmentation, pseudolites, and data link services, as applicable, shall be established.
6.3.4. RNP. The aircraft system response to loss of the navigation service(s) used to conduct the RNP operation shall be established.
a. The aircraft system response during any switch over to alternate navigation services shall be established.
b. It shall be demonstrated that the airplane will maintain the required flight path within the containment limits
(i.e., 2 times the RNP value) when un-annunciated failures not shown to be extremely remote (probability on the order of 10-7 per approach, or less) are experienced.
Appendix 3
6.4. Approach System Availability Requirements. Below 500 ft. on approach, the demonstrated probability of a successful landing should be at least 95% (i.e., no more than 5% of the approaches result in a go-around, due to the combination of failures in the landing system and the incidence of unsatisfactory performance). In addition, a dual or single area navigation (RNAV) approach system installation should meet the availability requirements consistent with the operational objective of 14 CFR part 121, section 121.349, (as applicable to standard Operations Specifications (OpSpecs)).
6.5. Go-around Requirements. A go-around may be required following a failure in the Approach System, as required by the flightcrew or by Air Traffic Service (ATS) at any time prior to touchdown.
a. It should be possible to initiate a missed approach at any point during the approach until touchdown on the runway. It should be safe to initiate a missed approach that results in a momentary touchdown on the runway.
b. A go-around should not require unusual pilot skill, alertness, or strength.
c. The proportion of approaches terminating in a go-around below 500 ft. (150 m), due to the combination of failures in the landing system and the incidence of unsatisfactory system performance, may not be greater than 5%.
d. Information should be available to the operator to assure that a safe go-around flight path can be determined.
6.6. Flightdeck Information, Annunciation, and Alerting Requirements. This section identifies information, annunciations, and alerting requirements for the flight deck.
The controls, indicators, and warnings must be designed to minimize crew errors that could create a hazard. Mode and system malfunction indications must be presented in a manner compatible with the procedures and assigned tasks of the flightcrew. The indications must be grouped in a logical and consistent manner and be visible under all expected normal lighting conditions.
6.6.1. Flightdeck Information Requirements. This section identifies requirements for basic situational and guidance information.
a. For manual control of approach flight path, the appropriate flight display(s), whether head down or head up, must provide sufficient information, without excessive reference to other cockpit displays, to enable a suitably trained pilot to:
(1) maintain the approach path,
(2) to make the alignment with the runway, and if applicable, safely flare and roll out, or
(3) go-around.
b. Sufficient information should be provided in the flight deck to allow the pilots to monitor the progress and safety of the approach operation, using the information identified above and any additional information necessary to the design of the system.
c. Required flight performance monitoring capability includes at least the following:
(1) unambiguous identification of the intended path for the approach, and, if applicable, safely flare and roll out, (e.g., ILS/MLS approach identifier/frequency, and selected navigation source), and
(2) indication of the position of the aircraft with respect to the intended path (e.g., raw data localizer and glide path, or equivalent).
Appendix 3
6.6.2. Annunciation Requirements. A positive, continuous, and unambiguous indication should be provided for the modes actually in operation, as well as those that are armed for engagement. In addition, where engagement of a mode is automatic (e.g., localizer and glide path acquisition), clear indication must be given when the mode has been armed by either action of a member of the flightcrew, or automatically by the system (e.g., a pre-land test - LAND 3).
6.6.3. Alerting. Alerting requirements are intended to address the need for warning, caution, and advisory information for the flightcrew.
6.6.3.1. Warnings. Section 25.1309 requires that information be provided to alert the crew to unsafe system operating conditions and to enable the crew to take appropriate corrective action. A warning indication must be provided if immediate corrective action is required. The design should account for crew alerting cues, corrective action required, and the capability of detecting faults.
6.6.3.2. Cautions. A caution is required whenever immediate crew awareness is required and timely subsequent crew action may be required. A means shall be provided to advise the flightcrew of failed airplane system elements that affect the decision to continue or discontinue the approach.
For RNP systems, the guidance or control system shall indicate to the flightcrew when the Actual Navigation Performance (ANP) exceeds the RNP Deviation alerting. The FAA does not require excessive deviation alerting, but will approve systems that meet appropriate criteria. If a method is provided to detect excessive deviation of the airplane, laterally and vertically during approach to touchdown, and laterally after touchdown, then it should not require excessive workload or undue attention. This provision does not require a specified deviation alerting method or annunciation, but may be addressed by parameters displayed on the Attitude Direction Indicator (ADI), Electronic Attitude Indicator (EADI), Head Up Display (HUD), or PFD. When a dedicated deviation alerting is provided, its use must not cause excessive nuisance alerts.
For systems demonstrated to meet criteria for Category II, compliance with the following criteria, from JAA AWO 236, is an acceptable means of compliance, but is not a required means of compliance:
a. For systems meeting the AWO 236 criteria, excess-deviation alerts should operate when the deviation from the ILS or MLS glide path or localizer centerline exceeds a value from which a safe landing can be made from offset positions equivalent to the excess-deviation alert, without exceptional piloting skill and with the visual references available in these conditions.
b. For systems meeting the AWO 236 criteria, excess-deviation alerts should be set to operate with a delay of not more than one (1) second from the time that the deviation thresholds are exceeded.
c. For systems meeting the AWO 236 criteria, excess-deviation alerts should be active at least from 300 ft. HAT (90 m) to the decision height, but the glide path alert should not be active below 100 ft. HAT (30 m).
6.6.3.3. System Status. Appropriate system status and failure annunciations suited to the guidance systems used, navigation sensors used, and any related aircraft systems (e.g., autopilot, flight director, electrical system) should be provided for the operator to determine prior to departure and the flightcrew to determine after departure, the capability of the airplane approach system components to accomplish the intended approach.
a. While en route, the failure of each airplane component affecting the approach capability should be indicated without flightcrew action. The indication should be an advisory (i.e., not a warning or caution, annunciates without flightcrew action, but does not demand immediate flightcrew attention), unless the failure requires a warning or caution for other reasons (e.g., autopilot disconnect warning).
b. A means shall be provided to advise the flightcrew of failed airplane system elements that affect the decision to continue to the destination or divert to an alternate.