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
(e.g., stall warnings, gear warning, or chip-detect).
18-4. Software Changes.
a. Changes to software that affect navigation functions should be carefully evaluated to determine if they are major changes to the equipment’s design approval (see 14 CFR 21.611 if part of a TSO’d article). Unless so ftware partitioning has been previously established, any change to level C or higher software in baro-VNAV equipment should be verified and validated to the appropriate level, and should be demonstrated to not inadvertently affect the remaining navigation functions.
Note: Baro-VNAV is typically included as a sensor function in FMSs that may have a TSO-C115(AR) authorization. Baro-VNAV is treated under TSO-C115(AR) similarly to inertial navigation systems that also do not have a separate TSO.
b. All software changes must be identified with the associated line replaceable unit using acceptable methods in accordance with the criteria in RTCA/DO-178B or ‘C’. Software changes in TSO approved equipment must be reported, as required, to the appropriate ACO. If the equipment displays a software identifier to the flight crew, the AFMS/RFMS (or appropriate placard) should indicate the approved identifier. Software changes incorporated in equipment already installed in an aircraft may require additional evaluation and possible flight manual revision prior to returning the aircraft to service, depending on the scope of the change.
18-5. Integration with GNSS-Provided Vertical Guidance.
a. Many aircraft integrations have implemented baro-VNAV for use in all phases of flight, and for vertical guidance on an LNAV/VNAV approach.
b. The applicant must address the following issues when the aircraft integration includes baro-VNAV and GPS/SBAS and/or GPS/GBAS vertical guidance:
(1) Transitions between GPS/SBAS or GPS/GBAS (GNSS height) and baro-VNAV vertical guidance should be smooth.
(a) Smooth guidance means there should be no transients or jumps between GPS/SBAS or GPS/GBAS guidance and baro-VNAV guidance in the vertical guidance displays that would indicate a sudden change in aircraft flightpath position.
(b) There should be no transients or jumps in vertical guidance commands that disrupt stabilized flight.
Note: For paragraphs 18-5.b(1)(a) and (b), minor transients or jumps may be acceptable depending on the integration. The applicant will need to demonstrate that minor transients or jumps do not adversely affect the aircraft flight path.
(c) Baro-VNAV performance has not been shown to be adequate for vertical guidance on LPV or GLS approaches.
(2) Transitioning from a GPS/SBAS vertically guided approach to LNAV/VNAV minimums using baro-VNAV must only occur prior to the FAF. If the aircraft is established on the final approach segment after passing the FAF using GPS/SBAS-provided VNAV, the transition must be to GPS/SBAS LNAV (vertical guidance flagged) if supported by the GPS/SBAS equipment.
(a) Issues with transitioning from GPS/SBAS to baro-VNAV vertical guidance on the final approach segment include:
(i) Temperature errors, particularly if the GPS/SBAS approach was started outside the allowable baro-VNAV temperature range.
(ii) MSL versus WGS-84 ellipsoid for path definition.
(iii) Curved baro-VNAV path versus straight GPS/SBAS path.
(iv) Linear baro-VNAV guidance versus angular GPS/SBAS guidance.
(b) These issues can cause discontinuities or jumps that could potentially de-stabilize the critical final approach segment and result in unacceptable pilot workload.
(3) Transitioning from a GPS/GBAS GLS approach to another procedure with LNAV/VNAV minimums using baro-VNAV must only occur prior to the FAF. There is no transition from a GPS/GBAS vertically guided approach after passing the FAF. After the FAF , a missed approach is necessary for a GPS/GBAS navigation or integrity disruption.
Note: GPS/GBAS approaches have a different naming convention from other RNAV approaches and will not have LNAV/VNAV or LNAV minimums published with the GLS procedure.
(4) It should be clearly indicated to the pilot whether the approach vertical guidance is based on GPS/SBAS, GPS/GBAS, or baro-VNAV.
(5) Baro-VNAV implementations demonstrating vertical containment about a fixed path in space may not need to differentiate between GPS/SBAS or GPS/GBAS VNAV and baro-VNAV. However, this should only be done when the vertical containment demonstrated with baro-VNAV clearly meets or exceeds the vertical performance requirements of GPS/SBAS or GPS/GBAS.
Note: There is no public standard for definition of “vertical RNP” nor does this guidance material intend to define “vertical RNP.” Future performance-based operations may define “vertical RNP.”
(6) Consideration should be given to operating manual descriptions and different procedural training between GPS/SBAS, GPS/GBAS and baro-VNAV.
(a) Effects of cold temperature deviations from International Standard Atmosphere must be considered for baro-VNAV operations, and whether or not the baro- VNAV equipment includes temperature compensation.
(b) Baro-VNAV may not be authorized at airports with remote altimeter settings.
(7) There should be an annunciation in the primary field of view indicating the active approach type (for example, GLS, LPV, LP, LNAV/VNAV, LNAV). The intent is to ensure the crew has an unambiguous indication of the active approach in the primary field of view that will correlate to a line of minima on the approach chart. Consideration may be given to the aircraft’s overall cockpit alerting philosophy to reduce the number of independent indicators.
18-6. Glidepath Low Deviation Alerting Function.
a. To help prevent controlled flight into terrain, manufacturers and operators of aircraft that install baro-VNAV capability are highly encouraged to install a glidepath deviation alerting function.
b. If implemented, baro-VNAV 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.