14-6.5 System Status.
The flight crew m ust have a means to evaluate the aircraft equipment’s capability to accomplish the approach operation. The flight crew must be advised of failed aircraft systems or equipment affecting the decision to continue to the destination or divert to an alternate.
Note: System status considerations also apply to IFR departure operations such as standard instrument departures. The flight crew must be advised of failed aircraft systems or equipment affecting the decision to depart.
14-6.6 Annunciations.
a. For installations containing m ore than one approach navigation source, the navigation source (for example, ILS, GPS/SBAS, baro-VNAV, 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 (LP/LPV, LNAV/VNAV, LNAV) must be clearly annunciated to the pilot 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, 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, or 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 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.
c. Changes in the approach type annunciations should be very clear and distinctive to quickly catch the flight crew’s attention. This is so the flight crew knows and understands that there h as been a change in service level and will make adjustments as needed to fly the appropriate approach minimums.
d. Aircraft installations containing both GPS/SBAS-provided vertical guidance and baro-VNAV vertical guidance capability should be carefully evaluated to ensure the annunciations clearly indicate the approach service provided and the sensor driving the vertical display (see paragraph 17-5).
14-6.7 Accessibility.
a. Single equ ipment 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).
14-6.8 GPWS/TAWS Glideslope Warning.
Aircraft with ILS capability that is in terfaced to GPWS or Class A TAWS with a glideslope warning function (Mode 5 GPWS alert) must also include the glideslope warning function during a GPS/SBAS LPV approach.
Note: There is no intent to differentiate between LPV approaches using a 35m VAL or 50m VAL in the FAS datablock. The guidance above is intended for all LPV approaches.
14-7. GPS/GBAS VDB Receiver.
This parag raph provides guidance related to the installation of a VDB receiver, including those embedded within a multi-mode receiver (MMR). This guidance applies to all installations, but is only expected to be specifically evaluated as part of the initial airworthiness approval (i.e., initial airworthiness approval may provide sufficient substantiation for follow-on installations).
14-7.1 Interference – EMC.
a. The VDB receiver m ay be susceptible to interference from VHF communications equipment on the aircraft.
b. At least 53 decibels relative to carrier power (dBc) of isolation is required to protect the VDB receiver from desensitization for horizontally polarized VDB antennas operating in the presence of a +40 decibels referenced to one milliwatt (dBm) (effective isotropically radiated power) vertically polarized VHF communications transmission. This isolation may be 83
achieved through a combination of 15 dBc of cross-polarization rejection and -38 dBc of antenna coupling.
c. The full 53 dBc m ust be achieved through antenna coupling for aircraft using a vertically polarized VDB antenna. It is not feasible to accomplish this isolation simply due to free space path loss: special considerations will be required.
14-7.2 Compatibility with other systems.
The VDB receiver m ay use the localizer or VOR antenna. If this involves introducing additional splitters in the RF path, the performance of the localizer or VOR receivers must be re-assessed due to the degradation in signal strength resulting from the splitter. The latest revisions of AC 23-8, AC 25-7, AC 27-1, and AC 29-2 provide guidance material on these installations.
14-7.3 VDB aircraft implementation loss.
The airc raft implementation loss should be less than 6 dB (gain) and greater than -15 dB (loss) for a horizontally polarized antenna, or less than 6 dB (gain) and greater than -11 dB (loss) for a vertically polarized antenna. The total implementation loss is the algebraic sum (in dBs) of the antenna gain (referenced to an isotropic radiator) and the attenuation (as a negative number) between the antenna and the VDB receiver. The attenuation includes line dissipation and voltage standing wave ratio (VSWR) mismatch losses. The implementation loss should be verified over the frequency range 108.000 to 117.95 MHz.
Note: Integrations that re-use VOR and localizer antennas may be problematic when trying to meet the -15 dB aircraft implementation loss allocation due to aircraft-level issues
(e.g., antenna patterns, cabling losses, splitters, connectors, etc.) and/or receiving the signal from any direction (see paragraph 5-4.1.b).
14-8. GPS/GBAS Navigation Computer Receiver.
This paragraph provides guidance related to the installation of GPS/GBAS equipm ent supporting GLS Category I approaches. This guidance applies to all installations, but is only expected to be specifically evaluated as part of the initial airworthiness approval (i.e., initial airworthiness approval may provide sufficient substantiation for follow-on installations).
14-8.1 GPS/GBAS equipment intended for Category I.
Category I approach operation m ust 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: GPS/GBAS no longer requires proof of concept testing to establish appropria te criteria for operational approval and certification testing for Category I as stated in AC 120-29a, appendix 2.
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 and/or TSO-C129a 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.
14-8.2 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 85
should be demonstrated at th is 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.
14-8.3 Performance and Performance Monitoring.
Sufficient infor mation 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).
14-8.4 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).
14-8.5 Continuity of Navigation.
a. Verify continuity of navigation data during norm al 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.
14-8.6 Fault Detection and Annunciation.
The autom atic 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.
14-8.7 System Status.
The f light 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.
14-8.8 Annunciation.
a. For installations containing m ore 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 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.
14-8.9 Accessibility.
a. Single equ ipment 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 m ore) 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).
14-8.10 Glidepath Capture.
Dem onstrate 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.
14-8.11 Equipment Qualification.
The GPS/GBAS positioning and navigation equipm ent 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.
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 GPWS/TAWS Glideslope Warning.
Aircraft with ILS capability that is in terfaced to GPWS or Class A TAWS with a glideslope warning function (Mode 5 GPWS alert) must also include the glideslope warning function during a GPS/GBAS precision approach.
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:
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:
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:
(1) The distance to active waypoint m ust 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 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.
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.
92 Note: 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.
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 0.25 Flight Director and Autopilot
1.0 0.5
0.8 Flight Director and Autopilot Manual CDI operation
2.0 1.0 Manual CDI operation
4.0 2.0 Manual CDI 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). If a moving map display is included with or interfaced to the positioning and navigation equipment, the map display should be capable of depicting the curved, RF leg segments without discontinuities on both active and inactive leg segments. 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, 93