14-8.12 Interoperability.
Any GPS/GBAS ground installation provided or used by the applicant for the purpose of perform ance 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.
14-8.13 GPS/GBAS Glideslope Low Deviation Alerting Function.
a. Aircraft with ILS capability that is in terfaced to GPWS or Class A TAWS (Mode 5 GPWS) alert for ILS deviations below the ILS glideslope must also include a glideslope alerting function during a GPS/GBAS precision approach.
b. The FAA understands that for digital-only systems, complying with the guidance in paragraph 14-8.13.a might not be possible without changes to the GPWS/TAWS system. There is no intent to force changes to the GPWS or TAWS functions, impact the GPWS or TAWS TSOA, or imply that GPWS or TAWS become the only means to provide the function. The intent for paragraph 14-8.13.a is to include an equivalent alert during GLS approaches for deviations below glideslope, but not necessarily through the GPWS or TAWS equipment. For example, GPS/GBAS vertical performance monitoring and alerting can be used to provide an equivalent glideslope alerting function if it is not accomplished through the GPWS or TAWS equipment.
c. This guidance reflects the AC 20-138B clarification policy memorandum signed on November 22, 2010 and replaces that memorandum.
14-9. Special Use Mission Equipment - Not for Navigation.
A special ap proval 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 25-10 (latest revision) provides additional guidance on miscellaneous, non-required equipment installations.
Chapter 15. Inst allation Considerations - RNAV Multi-Sensor Equipment.
15-1. Introduction.
When installing GNSS a s part of a multi-sensor system, the installation issues of chapter 14 apply and will take precedence if any conflicts with this chapter arise.
15-2. Interface to Primary Navigation Display.
Navigation data, including a TO/FROM indication and a failure indicator, m ust 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 indicated 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.
15-2.1 Non-numeric Deviation Displays.
a. Non-num eric 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 automatically 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.
15-2.2 Map Displays.
Map displays should give equivalent functionality to a non-num eric lateral deviation display described above, and be readily visible to the pilot with appropriate map scales (scaling may be set manually by the pilot.)
15-3. Interface to Remote Annunciator.
a. Multi-sensor equipm ent 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 97
98 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.
15-4. Unique Software Considerations.
a. If software was developed using RTCA/DO-178A procedures (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 pertinent airworthiness requirements is to comply with pertinent portions of the requirements contained in RTCA/DO-178B, 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-178B, as referenced in AC 20-115B (or later revision) to show that the software aspects of a system comply with pertinent airworthiness requirements. For software developed prior to the availability of RTCA/DO-178B, paragraph 12.1.4 of RTCA/DO-178B 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-178B.
Chapter 16. Inst allation Considerations - RNP.
16-1. Introduction.
This chapter contain s installation consideration guidance for basic RNP. RNP AR installation considerations are in appendix 2 of this AC.
16-2. Flight Technical Error.
The aircraft m anufacturer should verify maintenance of FTE (95% of the flying time) during straight path segments per Table 9 below. The FTE should be demonstrated in each phase of flight, both with and without autopilot and/or FD as applicable. The FTE values below are also acceptable for curved path segments only with an autopilot and/or FD. Manual flight operation on curved path segments will require a separate FTE evaluation.
RNP FTE FTE Basis
0.3 0.125
0.25 Autopilot Flight Director or Manual Operation
1.0 0.5
0.8 Flight Director or Autopilot Manual Operation
2.0 1.0 Manual Operation
4.0 2.0 Manual Operation Table 9. RNP FTE Performance
Note: Navigation systems providing RNP performance monitoring and alerting (such as GNSS) can satisfy this FTE requirement. These systems must ensure the TSE for each segment is not exceeded, and the integration of operational modes and configurations accounts for accuracy and FTE.
16-3. Radius to Fix (RF) Legs.
a. Paragraph 16-3 applies to equipm ent intended to support procedures with RF legs (see appendix 3). The map display should be capable of depicting the curved, RF leg segments without discontinuities on both active and inactive leg segments if a moving map display is included with or interfaced to the positioning and navigation equipment. Positioning and navigation equipment manufacturers should include a list of compatible moving map displays in the installation manual/instructions by part number, model, and/or software version as applicable to support RF leg capability.
b. It could be possible for applicants to provide mitigations for moving map displays that are not capable of depicting RF leg segments. The applicant needs to substantiate during the installation approval that FTE is monitored and controlled during the entire RNP operation, including the RF legs. For example, moving map display deficiencies may be mitigated by an aircraft equipped with an automatically slaved course selector and a sufficiently capable autopilot with a limitation for autopilot coupling during RNP operations with RF legs. Other solutions may be possible, but any solution must be documented in the installation instructions along with any limitations.
c. The installation applicant should analyze crew workload when flying and monitoring track adherence in association with RF legs during all phases of flight and determine the workload is acceptable, including those non-normal procedures that can be evaluated in flight.
d. Positioning and navigation equipment that does not support RF leg capability must have an AFMS/RFMS limitation stating the equipment cannot be used for RNP procedures containing RF legs.
16-4. Interface to FGS.
Verify acceptable autop ilot response to an RNP fault by 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 17. Inst allation Considerations - Baro-VNAV.
17-1. 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.
17-2. Manufacturer’s Instructions.
Baro-VNAV equipm ent should be installed in accordance with instructions and limitations provided by the manufacturer of the equipment.
17-3. Annunciations.
a. Visual annunciations must be consistent with the criticality of the annunciation and must be read able 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
(e.g., stall warnings, gear warning, or chip-detect).
17-4. Software Changes.
a. Changes to software that affect navigation functions should be carefully evaluated to determ ine if they are major changes to the equipment’s design approval (see 14 CFR 21.611 if part of a TSO’d article). Unless software 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. Software changes in TSO approved equipment must be reported, as required, to the appropriate ACO. If the equipment displays a software identifier to the flightcrew, 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.
17-5. Integration with GNSS-Provided Vertical Guidance.
a. Many aircraft integrations have im plemented baro-VNAV for use in all phases of flight, and can be used for vertical guidance on an LNAV/VNAV approach. 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 17-5.a(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 fro m 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, 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.
17-6. Glidepath Low Deviation Alerting Function.
a. For aircraft with ILS capability th at is interfaced to GPWS or Class A TAWS (Mode 5 GPWS) alert, the FAA recommends that applicants integrating baro-VNAV (i.e., TC or STC holders) include a glidepath alerting function for excess deviation below glidepath similar to a GPWS or TAWS alert for ILS deviations below the ILS glideslope. The intent for this function is to adopt the safety benefits of the ILS glideslope alert by including a similar alert during 103
104 baro-VNAV approaches for deviations below the final approach segment glidepath. However, the function need not be accomplished through the GPWS or TAWS equipment, although using the GPWS or TAWS equipment is certainly acceptable. The use of alerting for flight technical error or total system error can also meet this functional guidance.
Note: The applicant (i.e., TC or STC holders) should be cognizant of the existing alerts on the aircraft when implementing the baro-VNAV alert function. The alert function should not conflict with existing alerts or cause flightcrew human factors issues.
b. This baro-VNAV glidepath function should provide alerts similar to the GPWS/TAWS alert during ILS operations that occurs at 1.3 dots deviation low scaling. The FAA recognizes that performance scales for baro-VNAV may not match the ILS deviation scaling; particularly for non-temperature compensated equipment. It is acceptable for applicants to provide an alert when the below glidepath deviation exceeds 75 ft (i.e., the baro- VNAV FTE limits for approach operations).
c. Refer to the latest revision of TSO-C151 if using GPWS/TAWS for glidepath alerting during approaches using baro-VNAV.
Chapter 18. Inst alled Performance - Data Submittal.
18-1. Introduction.
This chapter identifies d ocumentation typically required by the aircraft certification authorities to support installation airworthiness approval. The information described in this chapter is applicable to obtaining an STC, amended STC, TC, or an amended TC.
18-2. Project Specific Certification Plan.
Provide a p lan that establishes the certification basis, how the program will be administered, method of compliance, and schedule. When establishing the certification basis, the plan should identify how the positioning and navigation equipment will meet the applicable airworthiness requirements and any special conditions. The FAA and Industry Guide to Product Certification (second edition) provides guidance on developing a project specific certification plan. Additional information can be found in the latest revision of AC 21-40.
18-3. TSO Technical Data.
Due to positioning and navigation equipm ent complexity, applicants applying for a TSOA/LODA should be prepared to provide data for the ACO to:
a. Evaluate applicant supplied bench test data on the equipment and verify that the tests comply with the relevant procedures and requirements.
b. Evaluate the applicant’s reliability data or analysis establishing that all probable failures affecting the navigation function are detected. Qualitative analysis may be used under the latest revision of AC 23.1309-1, AC 25.1309-1, AC 27-1, or AC 29-2 as appropriate.
c. Evaluate the applicant’s system safety assessment to confirm that all failure conditions have been identified, classified and described in functional and operational terms.
d. Verify compliance to the design assurance levels consistent with the failure condition classification for the equipment’s intended function.
(1) This verification includes confirming installation instructions have a summary of the equipment limitations relative to the design assurance levels, particularly if the criteria in AC 23.1309-1D for different classes of 14 CFR part 23 aircraft are applied. For example, TSO-C146c Class 3 equipment (GPS/SBAS stand-alone LPV capable equipment with a hazardous failure condition for HMI) that has software developed to RTCA/DO-178B Level C would state the following:
“This TSO-C146c equipment complies with paragraph 13a in AC 23.1309-1D for Class I, II, and III aircraft. This equipment is not eligible for installation in 14 CFR part 25, 27, 29 or part 23 Class IV aircraft unless the LPV approach mode is disabled through the following equipment configuration setting: ….”
18-4. Review the installation manual.
a. The applicant should include all known installation and perform ance limitations.
Special attention should be given to reviewing those limitations in light of the variety of different installation configurations that are supported.
b. The installation manual should include instructions for standard practices used in the installation and should address the unique equipment issues in chapters 11 through 22 of this AC.
c. Installation approvals are aided when the installation manual identifies which equipment is compatible with the newly installed positioning and navigation equipment, and/or provides detailed interface information. A data flow diagram can be a useful aid in depicting all the interfaces. Examples of typical installed equipment interfaces are: barometric altimeter, FMS, FGS, antenna(s), displays, deviation indicators, TAWS/HTAWS, ADS-B, external switches, and lightning detection. The applicant should consider developing information for the installation instructions on conducting ground and/or flight checks so the installer can ensure proper functioning of these interfaces. In addition, the installation manual should include instructions that address the critical areas unique to each installation, for example:
(1) Antenna placement;
(2) Unit placement (for controls/display);
(3) Equipment calibration and installed performance test procedures;
(4) Switching, external annunciations, configuration programming, and cockpit layout;
(5) Wiring diagrams of the installation process;
(6) Electromagnetic compatibility; and
(7) Interface compatibility.
d. Particular attention should be focused on the FGS and autopilot approach interface to ensure compatibility with the gain scheduling employed by some equipment during approaches. For example, some autopilots depend upon a radio altimeter, or, middle marker beacon passage inputs to enable a "glideslope extension" function to reduce "porpoising" or aerodynamic instability when coupled to a glideslope signal during the final approach phase.
But WAAS LPV approaches do not have middle marker beacons so autopilot response needs to be evaluated when incorporating LPV capability.
18-5. Structural Analysis.
The positioning and navigation equipm ent installation, including antenna, must be sufficient to meet all structural mounting, dynamic, and emergency landing loads appropriate to the aircraft. The installer must verify whether antenna installations penetrating the pressure 106