15-9.1 G PS/GBAS Equipment Intended for Category I.
Category I approach operation must provide for the following:
a. The GPS/GBAS approach and landing systems should meet the guidance set forth in AC 120-29 (latest revision), Criteria for Approval of Category I and Category II Weather Minima for Approach, appendix 2.
Note 1: GPS/GBAS no longer requires proof of concept testing to establish appropriate criteria for operational approval and certification testing for Category I as stated in AC 120-29a, appendix 2.
Note 2: AC 120-29a will be replaced soon with a new 90 series AC.
b. For installations where the GPS/GBAS sensor is integrated with other landing systems, such as an MMR, the “ILS look-alike” implies that the MMR signal to the autopilot is scaled in terms of depth of modulation (DDM) units, with sensitivity as described in RTCA/DO-253C, paragraph 2.3.11.5.1.1.1 and paragraph 2.3.11.5.1.2.1.
c. Aircraft integrating GPS/GBAS must have an RNAV capability for the initial, intermediate, and missed approach segments.
d. FMSs that are part of GPS/GBAS integrations should provide the RNAV capability for the initial and intermediate approach segments to place the aircraft in proper position for the GPS/GBAS equipment to conduct the GLS final approach segment. The FMS should also provide RNAV capability for the missed approach segment.
(1) RNAV capability for the initial, intermediate, and missed approach segments can be accomplished by the FMS according to its TSO-C115b (or later revision) or TSO-C146(AR), approval. However, to provide the RNAV function, the FMS will need the ability to recognize a GLS RWY XX approach procedure, store the appropriate segment information in the database, and recall the information as part of the selected approach procedure.
(2) FMS RNAV capability to support GPS/GBAS approaches should be addressed as part of the considerations for installation approval.
e. All installations should meet the constraints on the total differential group delay for the antenna, navigation computer receiver, and all cables/connections referenced in RTCA/DO-253C paragraphs 2.3.6.4 for GPS satellites and 2.3.6.5 for GPS/SBAS satellites.
15-9.2 GPS/GBAS Stand-Alone or MMR Equipment Intended for Category I.
When implementing GPS/GBAS to support GLS Category I operation either as stand-alone equipment or integrated as part of the MMR, the following criteria should be addressed:
a. The airplane’s system response to a loss of GPS/GBAS guidance should be no worse than a similar ILS event (minor) and should be free of objectionable transients and sustained oscillations.
b. The GPS/GBAS should be shown to be compatible with a GPS/GBAS service provision consistent with criteria contained in ICAO Annex 10 (as modified by amendment 84) or, accepted by ICAO for incorporation into Annex 10. It is noted that the GPS/GBAS ground facility approval process is outside of the airborne system approval process.
c. It should be possible to initiate a missed approach at any point during the approach down to the minimum altitude sought by the applicant for operational use. Safe go-around should be demonstrated at this minimum altitude.
Note: The presence of large navigation system errors (detectable only by pilot visual reference out-the-window) should not hinder the pilot’s decision to land or conduct a missed approach. Annex 10 integrity limits for Category I operations reference vertical errors as large as 35 m and lateral errors as large as 40 m.
15-9.3 Performance and Performance Monitoring.
Sufficient information must be provided in the flight deck to allow the crew to monitor the approach operation progress and safety. This in-flight performance monitoring must include:
a. Unambiguous identification of the intended path for the approach (e.g., approach type, approach identifier, frequency or channel number); and
b. Indication of the position of the aircraft with respect to the intended path (e.g., cross track and vertical deviation information).
15-9.4 Integrity.
The onboard landing system components, considered separately and in relation to the other associated onboard systems, should be designed to comply with the appropriate 14 CFR part 2X.1309, considering any specific safety-related criteria in the latest revision of AC 120-29, appendix 2 and the operating rules. Presenting misleading information to the flight crew on a GPS/GBAS approach should be considered a Hazardous failure condition (see Table
8).
Note: AC 120-29a will be replaced soon with a new 90 series AC.
15-9.5 Continuity of Navigation.
a. Verify continuity of navigation data during normal aircraft maneuvering on the GPS/GBAS approach.
b. Unlike ILS, where the ILS facility is always located in front of the aircraft on approach, a GPS/GBAS facility could be located anywhere with respect to the approach path.
Therefore, the flight test should verify VDB signal reception at all angles relative to the airframe.
15-9.6 Fault Detection and Annunciation.
The automatic means to detect and annunciate misleading guidance signals should have coverage and integrity similar to that of an ILS system when used in the approach flight phase and during go-around.
15-9.7 System Status.
The flight crew must have a means to evaluate the capability of the aircraft elements to accomplish the approach operation prior to and after departure. The flight crew must be advised of failed aircraft systems or components affecting the decision to continue to the destination or divert to an alternate airport.
15-9.8 Annunciation.
a. For installations containing more than one approach navigation source, the navigation source (for example, ILS, GPS/GBAS, etc.) selected for the approach must be positively indicated in the primary field of view. Consideration should be given to the overall aircraft-level annunciation philosophy.
Note: Aircraft requiring two pilots must have this
annunciation at each pilot station.
b. The approach type (GLS) must be clearly annunciated to the flight crew prior to and throughout the entire approach in the primary field of view.
(1) It is acceptable for a primary flight display to annunciate localizer/glideslope using an abbreviation such as LOC/GS, when the aircraft integration includes GPS/SBAS LPV, GPS/GBAS GLS Category I, and ILS. There must be an unambiguous indication the navigation source is provided by GPS/SBAS, GPS/GBAS, or ILS as appropriate in the primary field of view.
(a) LNAV/VNAV and LNAV approach types must still be annunciated when applicable if the applicant uses LOC/GS for LPV, GLS Category I, or ILS.
(2) It is acceptable for the primary flight display to annunciate azimuth/elevation using an abbreviation such as AZ/EL when the aircraft integration includes GPS/SBAS LPV, GPS/GBAS GLS Category I, and MLS. There must be an unambiguous indication the 125
navigation source is provided by GPS/SBAS, GPS/GBAS, or MLS as appropriate in the primary field of view.
(a) An unambiguous navigation source annunciation is still necessary if there is no MLS capability on the aircraft and AZ/EL is being used for a combination of only LPV and GLS Category I.
(b) LNAV/VNAV and LNAV approach types must still be annunciated, when applicable, if the applicant uses AZ/EL for MLS, LPV, or GLS Category I.
15-9.9 Accessibility.
a. Single equipment installations must be accessible and usable by the pilot. For aircraft requiring two crew members, the equipment should be accessible and usable by either pilot located at a pilot or copilot crew station.
b. Dual (or more) equipment installations must have a convenient and expedient way to update data, information and programs, and a means to ensure consistency between the equipment (e.g., a “cross-load” capability can ensure identical data).
15-9.10 Glidepath Capture.
Demonstrate that acceptable glide-path capture, followed by a stable approach, can be accomplished. This demonstration may include simulations and flight test evaluations.
Factors that influence an acceptable capture followed by a stable approach may include, but are not limited to, angular offset with the glide-path centerline, altitude at which the airplane acquires that centerline, airplane flying qualities, wind and turbulence conditions, flap settings and center of gravity conditions, and time interval required by the flight control computer algorithm to acquire stable signals.
Note: With some GPS/GBAS ground facilities, guidance may not be available until the aircraft is within 20 NM of the approach runway. This is because the differential corrections are used in the avionics only within a service region defined for the specific ground facility providing the approach. The ground facility VHF data broadcast indicates the limit of this service region. Although service regions smaller than 20 NM may be indicated, they would not meet the normal, minimum coverage required to support precision approach operations.
15-9.11 Equipment Qualification.
The GPS/GBAS positioning and navigation equipment should meet the minimum performance standard in TSO-C161a. The GPS/GBAS VHF data broadcast equipment should meet the minimum performance standard in TSO-C162a.
15-9.12 Interoperability.
Any GPS/GBAS ground installation provided or used by the applicant for the purpose of performance demonstration should be shown to be consistent with ICAO Annex 10, of Standards and Recommended Practices Applicable for Category I. The applicant must show that the GPS/GBAS ground installation complies with the requirements of ICAO Annex 10. If this compliance cannot be shown, the applicant should identify and evaluate differences between the GPS/GBAS Annex 10 requirements and the flight test site. The applicant should address the implications of those differences with respect to the validity of the flight test demonstrations and address any possible implications on aircraft interoperability when used with an ICAO Annex 10-compliant ground subsystem.
15-9.13 GPS/GBAS Glidepath Low Deviation Alerting Function.
a. To help prevent controlled flight into terrain, manufacturers and operators of aircraft that install a GPS/GBAS GLS approach capability are highly encouraged to install a glidepath deviation alerting function.
b. If implemented, GPS/GBAS vertical performance monitoring and alerting based on deviation guidance outputs (i.e., FTE) can be used to provide a glidepath deviation alerting function. The alert must be prominent and easily recognized by pilots and may be either aural or visual or both. Manufacturers may propose other alternatives.
15-10. Special Use Mission Equipment - Not for Navigation.
A special approval category for GNSS equipment is “Special Use -- Not for Navigation.” Systems that are installed for special use (agriculture, search and rescue, etc.) that will not be used for aircraft positioning or navigation can be approved on a non-interference basis using less strict airworthiness approval methods. Field approvals are normally acceptable for special use GNSS mission equipment. Inspectors should ensure the flight evaluation includes maneuvers that will normally take place while the GNSS equipment is in use and the equipment does not interfere with any required systems on the aircraft. AC 20-168 (latest revision), Certification Guidance for Installation of Non-Essential, Non-Required Aircraft Cabin Systems and Equipment and AC 20-169 (latest revision), Guidance and Certification of Military and Special Mission Modifications and Equipment for Commercial Derivative Aircraft (CDA) provides additional guidance on miscellaneous, non-required equipment installations.
Chapter 16. Installation Considerations - RNAV Multi-Sensor Equipment.
16-1. Introduction.
When installing GNSS as part of a multi-sensor system, the installation issues of chapter 15 apply and will take precedence if any conflicts with this chapter arise.
16-2. Interface to Primary Navigation Display.
Navigation data, including a TO/FROM indication and a failure indicator, must be displayed on a lateral deviation display such as a CDI, (E)HSI and/or a navigation map display.
If using a navigation map display, it should give equivalent functionality to a lateral deviation display and be readily visible to the pilot with appropriate map scales (scaling may be set manually by the pilot). The navigation data will be used as primary flight instruments for aircraft navigation, for maneuver anticipation, and for failure/status/integrity indication. The display of navigation parameters data should meet the following:
Note: See paragraph 8-3.g(2) for TO/TO navigation computer displays.
a. The navigation system in use must be clearly and unambiguously indicated for installations where multi-sensor outputs can drive a display that is shared in common with other navigation equipment (for example, VOR/DME, DME/DME/IRU, ILS, GNSS, baro-VNAV, etc.).
b. When in terminal and approach modes, the bearing and distance to the active waypoint must be displayed with a minimum resolution of 1 degree and 0.1 NM up to a range of 99.9 NM. Alternate means may be a moving map display where waypoint passage is clearly indicated. Waypoint passage may be indica ted with a waypoint alert (per latest revisions of AC 25-15, paragraph 5e(5)(iv) and AC 20-159); or, with VNAV guidance where level change is alerted and initiated upon sequencing the waypoints. If a moving map is provided, the map may obviate the need for a numerical output provided there is adequate resolution.
Note: Moving maps where the finest resolution is 5nm are inadequate to negate displaying a numerical value.
c. Navigation data, including a TO/FROM indication and a failure indicator, must be displayed on a lateral deviation display such as a CDI, (E)HSI and/or a navigation map display.
These navigation data will be used as primary flight instruments for aircraft navigation, for maneuver anticipation, and for failure/status/integrity indication. The data should meet the following:
Note: See paragraph 8-3.g(2) for TO/TO navigation computer displays.
16-2.1 Non-numeric Deviation Displays.
a. Non-numeric cross-track deviation must be continuously displayed in all navigation modes.
b. Non-numeric deviation displays (for example, a CDI or (E)HSI) with a TO/FROM indication and a failure annunciation should have the following attributes:
Note: See paragraph 8-3.g(2) for TO/TO navigation computer displays.
(1) The distance to the active waypoint must be displayed either in the pilot’s primary field of view or on a readily accessible display page unless there are alternate means to indicate waypoint passage.
(2) Non-numeric vertical deviation must be continuously displayed when in an approach mode containing vertical guidance.
c. The lateral deviation scaling must be consistent with any alerting and annunciation limits, if implemented.
d. The lateral deviation display must also have a full-scale deflection suitable for the current phase of flight and must be based on the required total system accuracy.
e. The display scaling may be set automatically by default logic or set to a value obtained from a navigation database. The full-scale deflection value must be known or must be available for display to the pilot commensurate with enroute or terminal values.
f. The lateral deviation display must be automatically slaved to the RNAV computed path. The course selector to the deviation display should be autom atically slewed to the RNAV computed path or the pilot must adjust the omni bearing selector (OBS) or HSI selected course to the computed desired track.
Note: The normal function of stand-alone GNSS equipment meet this criteria.
16-2.2 Map Displays.
Map displays should give equivalent functionality to a non-numeric lateral deviation display described above, and be readily visible to the pilot with appropriate map scales (scaling may be set manually by the pilot.)
16-3. Interface to Remote Annunciator.
a. Multi-sensor equipment may drive remote annunciators in the primary field of view.
b. Visual annunciations must be consistent with the criticality of the annunciation and must be readable under all normal cockpit illumination conditions. Visual annunciations must 129
not be so bright or startling as to reduce pilot dark adaptation.
c. Waypoint sequencing, start of a turn, turn anticipation, TO/FROM indication, approach mode annunciation, and automatic mode switching should be located within the pilot’s primary field of view or on a readily accessible display page.
Note: See paragraph 8-3.g(2) for TO/TO navigation computer displays.
d. The multi-sensor equipment should provide annunciations for loss of integrity monitoring, loss of navigation, TO/FROM indication, and approach mode annunciation within the primary field of view.
Note 1: Loss of integrity monitoring is not applicable for GPS/SBAS Class Delta-4 implementations because this equipment only functions on the final approach segment (or its extension) where loss of integrity monitoring is defined as a loss of navigation. Normal loss of navigation indication is sufficient.
Note 2: See paragraph 8-3.g(2) for TO/TO navigation computer displays.
16-4. Unique Software Considerations.
a. If software was developed using RTCA/DO-178A (as is specified in TSO-C115a), the applicant may need to further evaluate some features of the software. RTCA/DO-178A does not address some applications of digital technology commonly found in multi-sensor equipment (e.g., use of user-modifiable software including data bases, option-selectable software, software development and verification tools, previously developed software in modular architectures, and field loadable software capabilities). In these cases RTCA/DO 178A does not provide adequate procedures and the applicant must include in the software aspects of certification plan the means for showing that these features comply with pertinent airworthiness requirements. One acceptable means for demonstrating such features comply with the airworthiness requirements is to comply with pertinent portions of the requirements contained in RTCA/DO-178B or ‘C’, which would supplement the basic requirements contained in RTCA/DO-178A.
b. The FAA strongly recommends that the applicant use the procedures described in RTCA/DO-178C, as referenced in AC 20-115C to show that the software aspects of a system comply with pertinent airworthiness requirements. For software developed prior to the availability of RTCA/DO-178C, AC 20-115C provides a method for upgrading a baseline for software development so that changes can be made in accordance with the requirements contained in RTCA/DO-178C.
16-5. Installed Performance Capability.
a. It is essential that procedures or optional functions an aircraft is not capable of performing are either removed from the RNAV multi-sensor equipment database, or otherwise inhibited, even if the avionics do support the function. The AFM(S)/RFM(S) must contain an appropriate entry for any limitations (see paragraph 12-7 and 12-8).
b. Data Quality Requirements (DQRs) for installed databases are normally addressed at the equipment design level. The DQRs applicable to the intended function must be confirmed at the aircraft level during airworthiness approval. A Type 2 LOA may be used to ensure the database requirements, including tool qualification, is appropriate for the intended function of the installed equipment. A Type 2 LOA also provides evidence the data quality characteristics are described and valid for the compatible equipment listed on the LOA (see paragraph 19-8).
Chapter 17. Installation Considerations - RNP.
17-1. Introduction.
This chapter contains installation consideration guidance for RNP. RNP AR installation considerations are in appendix 2 of this AC and Advanced RNP Function installation considerations are in appendix 3.
17-2. F light Technical Error.
The aircraft manufacturer should verify maintenance of FTE (95% of the flying time) per Table 9 below. Alternate FTE values may be demonstrated using the methods described below.
RNP (nm) FTE (nm) FTE Basis
0.3 0.125
0.25 Autopilot Flight Director or Manual Operation
1.0 0.5 Autopilot, Flight Director or Manual Operation
2.0 1.0 Autopilot, Flight Director or Manual Operation
4.0 2.0 Autopilot, Flight Director or Manual Operation Table 9. RNP FTE Performance Note: Table 9 is consistent with current information in RTCA/DO-283B for GPS and was derived from data in RTCA/DO-208 appendix E.
a. FTE assessments for approach, missed approach, or other defined operations, may be made by an aircraft manufacturer, avionics manufacturer, or operator to establish alternate values of expected FTE to be used for navigation system or procedure authorization. The alternate FTE values may then be applied toward TSE in lieu of using the standard FTE values shown in Table 9.
b. FTE values may be established by analysis (e.g., of existing data), by simulation
(e.g., in a suitable flight training simulator), through flight verification (e.g., data collected from flight demonstration(s) with an appropriately configured aircraft), or any combination of these methods. The FTE assessment should produce repeatable, consistent FTE level(s) and should key to:
• Types of procedures to be flown;
• Operations being normal or not (i.e., normal, non-normal, rare normal, etc.);
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• Pilot capability; and
• System variability.
c. The advantage to using lab analysis and engineering simulation for FTE assessments is the possibility to reduce the number of aircraft demonstrations. The number of planned aircraft demonstrations can be reduced when the initial aircraft demonstration data mimics and validates the FTE performance data collected through analysis and engineering simulation.
17-3. Radius to Fix (RF) Legs.
All information on RF legs is consolidated into appendix 3 (see paragraph A3-2).
17-4. Interface to FGS.
a. Verify autopilot compatibility with the installed navigation system RNP capability.
Refer to the appropriate installation guidance chapters for the navigation system.
b. Verify acceptable autopilot response to an RNP fault by simulating a representative fault consistent with the equipment architecture (e.g., pulling the circuit breaker) for the RNP equipment. The aircraft manufacturer or installer should complete this test in each of the RNP and autopilot modes, as applicable.
--- Chapter 18. Installation Considerations - Baro-VNAV.
18-1. Failure Protection.
Any probable failure of the airborne baro-VNAV system should not degrade the normal operation of other required equipment or create a flight hazard. Normal operation of the baro-VNAV equipment installation should not adversely affect the performance of other aircraft equipment.
18-2. Manufacturer’s Instructions.
a. Baro-VNAV equipment should be installed in accordance with instructions and limitations provided by the manufacturer of the equipment.
b. A special concern is using baro-VNAV vertical path guidance on published instrument procedures due to potential anomalies. A baro-VNAV airworthiness approval must have language in the installation instructions for an AFM(S)/RFM(S) limitation on baro-VNAV vertical path guidance. The limitation is that flight crews/pilots must not rely solely on the baro-VNAV vertical path guidance for compliance to published altitude restrictions during SIDs, STARs and LNAV or LP approach procedures. The flight crew/pilots must use the primary barometric altimeter to confirm compliance with all published altitude restrictions.
This includes use of the primary barometric altimeter to ensure compliance with all step-down fixes in the final approach segment of an instrument approach (see paragraph 12-8). The AFM(S)/RFM(S) (or equivalent documentation) limitation language must be equivalent to the following:
“When using the <insert name> VNAV system, the barometric altimeter must be used as the primary altitude reference for all operations; including instrument approach procedure step-down fixes.”
Note: Baro-VNAV systems certified before 11/20/1989 may have been certified to a lesser standard that is not consistent with a major failure condition. Operators of these aircraft should apply the final approach segment step-down fix to the LNAV/VNAV line of minima and should use the primary barometric altimeter to ensure meeting the step-down fix altitude constraint.
18-3. Annunciations.
a. Visual annunciations must be consistent with the criticality of the annunciation and must be readable under all normal cockpit illumination conditions. Visual annunciations must not be so bright or startling as to reduce pilot dark adaptation.
b. Audible alarms should be sufficiently loud and of appropriate pitch quality, duration and pattern. Alarms should be easily deactivated (but not easily deactivated inadvertently).
Audible alarms must not interfere with other aircraft audio alarms or alerts of higher priority 134