AC 20-191 condition prevents it f rom meeting the performance specified in sections
3.2.3 and 3.2.4. The removal of guidance alone is not adequate annunciation. Alerts must be timely, unambiguous, readily evident to each flight crew member, and compatible with the alerting philosophy of the airplane. Annunciations must be located to ensure rapid recognition and must not distract the pilot making the takeoff or significantly degrade the forward view.
3.2.5.3.1 Annunciations.During takeoff, whenever the takeoff guidance system does not provide valid guidance appropriate for the takeoff operation, it must clearly annunciate the failure to the flight crew, and the invalid guidance must be removed. The location of the annunciation must be positioned to ensure rapid recognition without distracting the pilot or significantly degrading the forward view.
3.2.5.3.2 Warnings.The takeoff guidance system must provide warnings for conditions requiring immediate pilot awareness and action
(e.g., failure of the guidance system).
3.2.5.3.3 Cautions.The takeoff guidance system must provide cautions for conditions requiring immediate pilot awareness and possible subsequent pilot action. These alerts need not generate a Master Caution light that would be contrary to the takeoff alert inhibit philosophy. Caution annunciations should not cause flight crew distraction during takeoff roll.
3.2.5.3.4 Advisories.The takeoff guidance system must provide advisories for conditions requiring pilot awareness in a timely manner. It should not generate advisories after takeoff commences.
3.2.5.3.5 System Status.
The takeoff guidance system should provide a system status
(e.g., status of built-in test equipment (BITE)/self-test).
3.2.6 Availability.
The probability of loss of takeoff guidance system should be remote.
3.3 Airborne Systems for Takeoff.
This section covers the criteria for a HUD that is integrated with ILS localizer or GBAS signals. In all cases, this AC assumes the sensors used for approach and landing will guide the aircraft during takeoff.
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AC 20-191
3.3.1 HUD for Ta keoff Guidance.
The following criteria apply if an applicant employs a HUD to provide takeoff guidance:
3.3.1.1 The workload associated with use of the HUD must comply with 14 CFR §§
23.2610, 25.1523, 27.1523, or 29.1523 as applicable. Reference AC 23.1523 and AC 23.1311-1; AC 25.1523-1 and AC 25-11, AC 27-1; or AC 29-2 as applicable for additional guidance.
3.3.1.2 The HUD installation and display presentation must meet 14 CFR §§
23.2600(a), 25.773, 27.773, or 29.773 as applicable. Reference AC 23.1311- 1; or AC 25.773 and AC 25-11, appendix F; or AC 27-1; or AC 29-2 for additional guidance.
3.3.1.3 For the entire takeoff path and for all normal and non-normal conditions, except loss of the HUD itself, the HUD takeoff system must provide acceptable guidance and flight information to enable the PF to complete the takeoff or abort the takeoff. HUD takeoff system use should not require excessive workload, exceptional skill, or excessive reference to other cockpit displays.
3.3.2 GBAS.
An applicant may use the guidance in this chapter to obtain airworthiness approval of a GBAS receiver for low visibility takeoff guidance. In addition, the applicant must evaluate the effect of loss and signal reacquisition during takeoffs .
3.4 Takeoff Guidance Evaluation.
An applicant should submit performance data for components used for takeoff guidance.
3.4.1 Certification Plan .
The applicant should provide a certification plan that includes a description of the aircraft systems, the certification basis, the certification methods, and compliance documentation. The certification plan should describe how any non-aircraft elements relate to the operation of aircraft systems from a performance, integrity, and availability perspective.
3.4.1.1 For ILS-based system elements, the applicant can predicate satisfaction of these performance provisions upon compliance with the ICAO Standards and Recommended Practices (SARPs), equivalent State standard, or by reference to an acceptable standard for performance of any navigation service.
3.4.1.2 For a Global Navigation Satellite System (GNSS) based system such as GBAS, the applicant can predicate satisfaction of these performance 3-9
AC 20-191 provisions upon compliance with either the ICAO SARPs, or equivalent State s tandards. The applicant should address any gaps or shortfalls in performance and how they relate to the aircraft system certification plan.
3.4.1.3 The certification plan should describe any new or novel system concepts or operational philosophy as applicable. The FAA will determine the need for additional criteria and provisions beyond this AC.
3.4.2 Performance Evaluation.
For new systems and any significant changes to an existing system, the applicant should demonstrate the performance of the aircraft and its systems by flight tests. Flight tests should include those maneuvers that are reasonably representative of actual expected conditions and should cover the range of parameters affecting the behavior of the aircraft (e.g., wind speed, ILS, or GBAS characteristics, aircraft configurations, weight, center of gravity, and non-normal events).
3.4.2.1 The performance evaluation should verify the takeoff guidance system meets the centerline tracking performance guidance specified in section
3.2.3.6.
3.4.2.2 The applicant should demonstrate the system performance in non-visual conditions for:
• Normal operations,
• Engine failure cases, and
• Recovery from displacements from non-normal events.
3.4.2.3 The applicant should demonstrate this performance to have a satisfactory level of workload and pilot compensation. The methods defined in AC 25-7 or AC 23-8 are acceptable.
3.4.2.4 The applicant should show the takeoff guidance meets its stated performance criteria without the use of any outside visual references.
Note: The pilot may begin the takeoff using external visual reference, but from a speed no greater than 50% of V1, the pilot should follow the guidance commands as accurately as possible without using the external view. The applicant may need to safely integrate a view limiting means during the demonstration.
3.4.2.5 The takeoff guidance system performance demonstration should comprise a sufficient number of takeoffs to show the system meets its intended function under any foreseeable operating conditions. The number of takeoffs specified below is adequate for this compliance demonstration. Note, however, the FAA may require more demonstrations depending on aircraft characteristics and design, or difficulties encountered during testing.
• Twenty (20) normal, all-engine takeoffs, 3-10
AC 20-191
• Ten (10) completed takeoffs, with simulated engine failure at or after th e appropriate VFAILURE. The assessment must consider all critical cases, and
• Ten (10) rejected takeoffs, some with simulated engine failure just prior to V1, and at least one run with simulated engine failure at a speed less than VMCG.
Note 1: EASA’s AMC AWO 431 recommends a different number of takeoffs.
Note 2: An applicant may propose an alternate method of compliance in their certification plan or through issue paper. An example of an alternate method could be a reduced number of takeoffs for the takeoff guidance system performance demonstration with rationale for a reduction in flighttesting. Examples of rationale could include recognition for modeling and simulation testing done as part of the demonstration or a similar previously certified system with consistent flight test data.
3.4.2.6 The applicant may seek credit for an earlier demonstration of the takeoff guidance system. New testing of the aircraft may be necessary if the FAA deems credit for design similarity or performance is not appropriate. In cases where the aircraft’s performance dynamics associated with retarding the throttle to idle do not adequately simulate the dynamics of an engine failure, the FAA may require an actual engine shutdown.
3.4.2.7 The applicant should demonstrate the takeoff guidance system performance with headwinds for which credit is sought, and at least 150 percent of the tailwinds, and crosswinds for which credit is sought. Headwinds and crosswinds must be 15 knots or greater.
3.4.2.8 The applicant should demonstrate the operation does not exhibit any guidance or control characteristics that would cause the flight crew to react in an inappropriate or unsafe manner.
3.4.2.9 The demonstration aircraft should be configured with the appropriate instruments to record the time history of track with respect to the extended runway and the climb profile after liftoff to a reasonable point (e.g., departure end of the runway) as a means to show satisfactory performance.
3.4.2.10 The applicant should demonstrate no display or failure characteristics degrade the flight crew’s ability to adequately monitor takeoff performance.
Examples of takeoff performance parameters to monitor include acceleration, engine performance, takeoff speed callouts, attitude, and airspeed. The demonstration should include the entire takeoff, and transition 3-11
AC 20-191 to the enroute climb speed and configuration, for all normal, abnormal, and emergency situations.
3.4.2.11 The performance evaluation must demonstrate that the takeoff guidance system provides command information as lateral guidance, which will enable maintaining the aircraft on the runway during the takeoff roll through acceleration to liftoff or, during a deceleration to a stop during a rejected takeoff. The evaluation must also demonstrate the failure annunciation criteria of section 3.2.5, as well as the crew’s ability to immediately detect and mitigate non-annunciated failures.
3.4.2.12 The applicant should demonstrate the aircraft system response to loss of the takeoff guidance signal and appropriate annunciation to the flight crew.
3.4.2.13 Pilot Experience Levels. The applicant must demonstrate the takeoff guidance system meets the performance provisions in this chapter with pilots of varying experience levels.
3.4.2.14 Failure cases should typically be spontaneous and unpredictable on the subject’s or evaluation pilot’s part.
3.4.3 Safety Assessment.
In addition to any specific safety-related criteria identified in this chapter, the applicant must conduct a safety assessment of all aircraft’s takeoff system and associated components, considered separately and in conjunction with other systems, to show compliance with §§ 23.2500, 23.2510, 23.2605, 25.1309, 27.1309, or 29.1309 per the guidance contained in AC 23.1309-1, 25.1309-1, AC 27-1, or AC 29-2, respectively.
3.4.3.1 The applicant must consider the responses to failures of navigation facilities, taking into account pertinent criteria for navigation facilities.
3.4.3.2 The applicant’s documented safety analysis conclusions must include:
3.4.3.2.1 Pursuant to §§ 23.2500, 23.2510, 23.2605, 25.1309 , 27.1309, or 29.1309, a Functional Hazard Assessment (FHA) conducted in accordance with AC 23.1309-1, AC 25.1309-1, AC 27-1, or AC 29-2, respectively; results summary from the fault tree analysis, demonstrated compliance, and probability determinations for significant functional hazards.
3.4.3.2.2 Information regarding “alleviating flight crew actions” considered in the safety analysis. This information should list appropriate alleviating actions and be consistent with the test validation. If alleviating actions are identified, the applicant should describe the alleviating actions in a form suitable to aid in developing:
• Pertinent provisions of the Aircraft Flight Manual (AFM) 3-12
AC 20-191 procedures section(s)
• Flig ht Crew Operating Manual (FCOM) provisions, or equivalent
• Pilot qualification criteria (e.g., training requirements, Flight Standardization Board (FSB) provisions)
• Any other reference material necessary for an operator or flight crew to use the system safely.
3.4.3.2.3 Information to support preparation of any maintenance and preventive maintenance procedures necessary for safety, such as:
• Certification Maintenance Requirements (CMR),
• Periodic checks, or
• Other checks, as necessary (e.g., return to service).
3.4.3.2.4 Information applicable to lim itations, as necessary.
3.4.3.2.5 Information necessary for development of Non-normal Procedures.
3.5 AFM.
Pursuant to 14 CFR §§ 23.1581, 25.1581, 27.1581, or 29.1581, as applicable, an applicant must furnish AFM with each aircraft. The AFM should contain the following information:
3.5.1 The criteria and configurations used for the takeoff system demonstration.
3.5.2 Any constraints or limitations necessary for safe operation.
3.5.3 Acceptable normal and non-normal procedures.
3.5.4 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 s known to be unacceptable for use (e.g ., ILS localizer or GLS) .
3.5.5 Applicable atmospheric conditions under which the system was demonstrated (e.g., headwind, crosswind, tailwind).
3.5.6 All necessary performance, procedure, or configuration data to permit an operator to determine climb gradient and transition distances for safe obstacle clearance during a takeoff operation ; 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 3-13
AC 20-191 operator and manufacturer (e.g., Flight Crew Operating Manual (FCOM), su pplementary performance information, separate AFM appendix).
3.5.7 For a takeoff system meeting the provisions of this chapter, the Normal Procedures, Normal Operations, or equivalent section, of the AFM should also contain the following statements:
• “The airborne system has been demonstrated to meet the airworthiness guidance of AC 20-191 (Chapter 3) for [specify the pertinent takeoff capability section(s) criteria met] when the following equipment is installed and operative:”
• “[list pertinent equipment]”
• “This AFM provision does not constitute operational approval for low visibility takeoff use of the system.”
3-14
AC 20-191 CHAPTER 4. CATEGORY (CAT) II
4.1 Introduction.
4.1.1 This chapter contains airworthiness approval criteria for equipment used to conduct a CAT II weather minima approach using certain radio na vigation aids (navaids) such as ILS or GBAS. This chapter does not provide criteria for each potential combination of aircraft and non-aircraft elements.
4.1.2 This chapter addresses the approach phase of flight, beginning at the Final Approach Fix (FAF) and ending at the CAT II Decision Height ( DH).
4.1.3 ICAO Annex 10 includes standards for ILS, MLS, and GBAS intended to support CAT II operations. This chapter addresses approval of equipment for operations using either ILS class (II/D/2) or better performance or GBAS facility classification (D/G1/any/any 1). This chapter addresses ILS avionics with Technical Standard Order (TSO)-C34e, TSO-C36e authorization, and GBAS avionics with the latest TSO- C161b and TSO-C162b authorization.
Note 1: While the airworthiness criteria for the guidance system for the approach and landing system applies from the FAF to the DH, guidance should be available down to half the DH.
Note 2: GBAS approach service volume is defined in ICAO Annex 10 Amendment 91.
4.1.4 The standards for GBAS ( RTCA DO-253D Change 1 and ICAO Annex 10) define two general classes of GBAS service, Approach Services and the GBAS Positioning Service. The standards further diffe rentiate GBAS approach services into multiple types referred to as GBAS Approach Service Types (GAST). A GAST is defined as the matched set of airborne and ground performance and functional requirements intended to be used in concert to provide approach guidance wi th quantifiable performance.
4.1.5 GBAS GAST C is the approved GBAS to support CAT I level of service. Applicants for CAT II airworthiness approvals typically seek approval through GBAS GAST D level of service using GBAS airborne equipment class ( GAEC) D. Applicants seeking CAT II airworthiness approval using GAST C and GAEC C avionics with TSO- C161b and TSO-C162b authorization need to show equivalence to performance achieved with ILS II/D/2 with additional criteria, limitations , and exceptions as 1 RTCA DO-253D Change 1, appendix I, contains a detailed discussion of approach service types, facility classification and airborne equipment classification for GBAS.
4-1
AC 20-191 determined by the FAA .
4.2 Airworthiness Criteria.
4.2.1 Airborne Equipment.
Airborne equipment meeting the airworthiness criteria contained in this chapter for the CAT II landing system satisfy the operational requirements of CAT II ILS found in AC 120-118. The basic airworthiness criteria rely on meeting the specific airworthiness performance provisions and are independent of the specific implementation in the aircraft or the type of approach system selected for the approach.
4.2.2 Applicant’s Proposal.
The applicant’s proposal for type certification approval for the equipment, system installations, and test methods should include factors such as the intended function of the installed system, its accuracy, reliability, and fail-safe features.
4.2.3 Intended Flight Path.
The applicant may establish the intended flight path in a number of ways, for example using a navigation aid (e.g., ILS, GBAS, etc.). Other methods may be acceptable if the applicant can show feasibility through other means (e.g., se nsing of the runway environment such as surface, lighting or markings or both with a vision enhancement system).
4.2.4 Onboard Navigation Systems.
Onboard navigation systems may have various sensor elements by which to determine the aircraft’s position. The sensor elements may include ILS, GBAS, or inertial information. Each of these sensor elements must perform within its appropriate limitations with regard to accuracy, integrity, and availability.
4.2.5 Indications.
The system must provide indications of the aircraft position with respect to the intended flight path. A list of accepted means of providing these indications to the pilot includes:
• Deviation displays with reference to navigation source (e.g., ILS receiver, GLS receiver, etc.)
• Onboard navigation system computations with corresponding displays of position and reference path
• Vision enhancement system, if applicable.
4.2.6 Approach System Accuracy Criteria.
The criteria for acceptable approach performance are based upon acquiring and tracking the required flight path to the appropriate approach procedure’s minimum altitude. The acquisition should be accomplished in a manner compatible with instrument procedure requirements and flight crew requirements for the type of approach being conducted.
4-2
AC 20-191
4.2.6.1 Appr oach Guidance System.
The approach guidance system must not generate sustained oscillatory command information (e.g., flight director, HUD, etc.) or require unusual effort by the pilot to control the flight path.
4.2.6.2 Lateral and Vertical Tracking Performance.
The applicant must show the system will meet the following performance.
4.2.6.2.1 Lateral tracking performance f rom 1000 ft. Height Above Touchdown (HAT) to 300 ft. HAT will be stable without large deviations (i.e., within ±50 microamps deviation or equivalent) from the indicated course or path.
4.2.6.2.2 Lateral tracking performance from 300 ft. (HAT) down to 100 ft. HAT will be stable without large deviations (i.e., within ±25 microamp s deviation) from the indicated course, for 95% of the time.
4.2.6.2.3 Vertical tracking f rom 700 ft. HAT to 300 ft. HAT should be stable without large deviations (i.e., within ±75 microamps deviation or equivalent) from the indicated course or path.
4.2.6.2.4 Vertical tracking performance from 300 ft. HAT down to 100 ft. HAT will 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. When applying this provision to path tracking in conjunction with CAT III, momentary excursions up to ±75 microamps during test demonstrations may be acceptable if the applicant shows satisfactory performance of the flight guidance system through touchdown and landing.
Note: The performance standards for ILS or GBAS GAST D signal in space contained in ICAO SARPs Annex 10, or an equivalent State standard, are acceptable standards for operations based on an ILS or GBAS, respectively.
4.2.7 Approach System Integrity Criteria .
Pursuant to §§ 23.2500, 23.2510, 23.2605, 25.1309, 27.1309, or 29.1309, the onboard components of the landing system, when considered separately and in relation to other associated onboard systems, must consider all specific safety related criteria identified in this AC, or as identified in accordance with the operating rules. The applicant can use the following criteria as advisory material for the application of §§ 23.2500, 23.2510,
23.2605, 25.1309, 27.1309, or 29.1309 to Approach and Landing Systems:
4.2.7.1 ILS.
The applicant must establish the aircraft system response to loss of ILS 4-3
AC 20-191 guidance signals (localizer (LOC) or glideslope (GS)). The applicant must also establish the aircraft system response during a switchover from an active LOC or GS transmitter to an optional backup transmitter.
4.2.7.2 GLS.
The applicant must establish the aircraft system response to loss of GLS guidance signals.
4.2.7.2.1 When using GBAS, the required flight path is uplin ked to the aircraft after the approach has been selected. This path will be used for flight guidance or the autopilot or both when required to conduct an approach, landing, and rollout.
4.2.7.2.2 Corruption of the information contained in the received VHF Data Broadcast (VDB) to define the reference path is hazardous. Failure resulting in undetected changes to the approach path definitions data must be extremely remote.
4.2.7.2.3 The flight crew must not be able to modify information that relates to the critical definition of required flight path.
4.2.8 Approach System Continuity Criteria .
The applicant should verify the continuity of navigation during normal aircraft maneuvering while in approach. For GLS, this includes verifying VDB signal reception at all angles relative to the airframe, as the GBAS facility could be located anywhere with respect to the approach path.
4.2.9 Approach System Availability Criteria .
While on approach below 500 ft., 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).
4.2.10 Go-around.
4.2.10.1 Go-Around Safety.
An aircraft conducting a CAT II instrument approach must be capable of safely executing a go-around from any point in an approach prior to touchdown with the aircraft in a normal configuration or specified nonnormal configurations (e.g., engine out for multiengine aircraft).
4.2.10.1.1 A go-around should not require unusual pilot skill, alertness, or strength.
4.2.10.1.2 The system should have information indicating the availability of a safe go-around flight path.
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AC 20-191
4.2.11 Information, A nnunciation, and Alerting .
This section identifies the provisions for information, annunciations, and alerting.
4.2.11.1 Compliance.
The design of the Information, Annunciation, and Alerting must comply with §§ 23.2605, 25.1322, 27.1322, or 29.1322 as applicable. Reference AC
23.1311-1, AC 25.1322, AC 27-1, or AC 29-2 for additional guidance.
4.2.11.2 Information guidance.
This section identifies criteria for basic situational and guidance information.
4.2.11.2.1 The system must present the mode and system malfunction indications in a manner consistent with the human f actors cockpit design philosophy. The indications must be grouped in a logical and consistent manner and be visible under all expected normal lighting conditions.
4.2.11.2.2 For manual control of approach flight path, the appropriate flight display(s), whether head down (HDD) or HUD, must provide sufficient information, without excessive reference to other cockpit displays, to enable a suitably trained pilot to :
• Maintain the approach path,
• Make the alignment with the runway, and if applicable, safely flare and roll out, or
• Go-around.
4.2.11.2.3 The information provided along with any additional information necessary to the design of the system must be sufficient to allow the pilots to monitor the progress and safety of the approach operation .
4.2.11.2.4 The system must have flight performance monitoring to include at least the following:
• Unambiguous identification of the intended path for the approach, and, if applicable, flare and roll-out, (e.g., ILS approach identifier/frequency, and selected navigation source, GBAS Runway Path Identifier (RPI), approach service type, etc.).
• Indication of the position of the aircraft with respect to the intended path (e.g., raw data localizer and glide path, deviation from FAS or equivalent).
4.2.11.3 Annunciation.
The system should provide a positive, continuous, and unambiguous 4-5