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.
Chapter 19. Installed Performance - Data Submittal.
19-1. Introduction.
This chapter identifies documentation 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.
19-2. Project Specific Certification Plan.
Provide a plan 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.
19-3. TSO Technical Data.
Due to positioning and navigation equipment 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 of the system design 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-C146d 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 or ‘C’ Level C would state the following:
“This TSO-C146d 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: ….”
19-4. Review the installation manual.
a. The applicant should include all known installation and performance 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 12 through 23 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.
19-5. Structural Analysis.
The positioning and navigation equipment 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 139
--- vessel require a damage tolerance assessment of the installation, considering the unique installation and the aircraft TC airworthiness basis.
19-6. Power Supply.
Provide an electrical load analysis to verify that the total electrical load requirements are within the capabilities of the aircraft's electrical generating system. Verify that the supplied electrical power is consistent with applicable equipment reliability requirements. This includes describing the primary power bus for the equipment and how the equipment is powered in an emergency condition.
19-7. Environment.
Provide qualification data substantiating that the aircraft environment in which the positioning and navigation equipment is to be installed is appropriate to the environmental categories (or criteria) in the appropriate RTCA/DO-160 revision per the TSO to which the equipment has been tested.
Note: Equipment produced to different TSO revisions can reference different RTCA/DO-160 revisions for environmental testing. Manufacturers may use later RTCA/DO-160 revisions than what is stated in the TSO, but their ACO will need to approve a deviation request to document the change.
19-8. Database.
a. AC 20-153 (latest revision) defines an acceptable means of ensuring that the aeronautical data process does not corrupt data, from the publication of data by the originating source to its application in the equipment, for those navigation systems that comply with the latest revisions of ACs 90-100 and 90-105. The TSOA provides sufficient evidence for compliance to AC 20-153(latest revision) for the installation approval, but operational approval for IFR use is based upon a database assurance process through a type 2 LOA. A type 2 LOA provides database objective evidence of integrity consistent with the monitoring and alerting requirement for GNSS and other RNP systems.
b. Verify the navigation database type 2 LOA exists with reference to AC 20-153 (latest revision). If there is no evidence of a Type 2 LOA, it is appropriate to place a limitation in the AFM(S)/RFM(S) stating “Not approved for IFR operations without a Type 2 LOA.”
19-9. Operations manual or AFMS/RFMS.
An AFMS/RFMS must be provided that contains the limitations and operating procedures applicable to the installed equipment configuration. The AFMS/RFMS must address the operation of the equipment and the related components as they are installed (e.g., remote source selector). An AFM/RFM supplement is required if the installation is based on a prior approval that had an AFM/RFM, or if there are any limitations associated with the operation of the equipment. See paragraph 15-4 for additional documentation considerations 140
specific to GNSS.
19-10. Stand-Alone Navigation Equipment.
Navigation systems designed as a combination navigation computer/sensor configuration must develop a pilot’s guide and a quick reference guide. These guides are typically developed by the equipment manufacturer.
a. Pilot’s Guide.
An operations manual (pilot’s guide) describing the equipment, functions and procedures must be provided with the positioning and navigation equipment. It is essential that the pilot’s guide be complete, concise, and easy to understand. Have an FAA flight test pilot familiar with the equipment review the pilot’s guide and required training programs. This training program may be a series of manuals, a videotape, interactive CD-ROM, etc. Due to the inherent complexity in area navigation operations, it is important that these training materials are useful and help pilots learn to operate the equipment.
b. Quick Reference Guide.
A quick reference guide must be provided with the positioning and navigation equipment as a training aid for the operation of the positioning and navigation equipment. The guide should be evaluated by a flight test pilot familiar with the equipment.
19-11. Ground and Flight Test Plans (functional and EMI/EMC testing).
The applicant must submit the proposed ground and flight test plans to demonstrate the equipment performance (as described in chapters 19 through 23), regulatory compliance, and EMI/EMC testing.
Chapter 20. Installed Performance - Test (General).
20-1. Intended Function.
Assess the ability for the equipment and aircraft combination to perform the intended function for the operation. The installed equipment may have the capability to perform an operation that is beyond the aircraft’s performance limit or current approval (or visa versa) and may require an AFMS/RFMS limitation. For example, a particular rotorcraft may only be approved for six degree steep angle approaches even though the installed equipment is capable of steeper angles.
20-2. Power Supply.
Assess all switching and transfer functions, including electrical bus switching, pertaining to the positioning and navigation installation.
20-3. Accuracy.
The accuracy of GNSS equipment is not a function of the installation, and should not be evaluated for each GNSS or multi-sensor installation. The accuracy of the GNSS equipment will be demonstrated during the sensor evaluation, typically as part of a TSOA/LODA.
20-4. Human Factors.
a. Visibility of the controls, displays, and annunciators relating to the installation should be evaluated during day and night lighting conditions. No distracting cockpit glare or reflections may be introduced and all controls must be illuminated for identification and ease of use. Night lighting should be consistent with other cockpit lighting.
b. Layout of the installed equipment should be evaluated with emphasis on equipment controls, applicable circuit breakers (labels and accessibility), switching arrangement, and related indicators, displays, annunciators, etc.
c. Manual approach selection or manual tuning of the approach should override any automatic selection. Once an approach has been selected, appropriate feedback to the pilot
(e.g., display of approach name (including runway), airport and reference path identifier) must be given to indicate the approach has been correctly selected.
d. Additional human factor considerations are in RTCA/DO-283B, appendix F.
Note: RTCA/DO-257 is currently under revision and may provide additional human factors information upon publication.
Chapter 21. Installed Performance - Test (GNSS).
21-1. Ground Test - GPS, GPS/SBAS, and GPS/GBAS.
21-1.1 Interference.
a. The lack of interference from VHF radios should be demonstrated on the completed GNSS installation by tuning each VHF transmitter to the frequencies listed below and transmitting for a period of 30 seconds while observing the signal status of each satellite being received. Degradation of individually received satellite signals below a point where navigation is no longer possible is not acceptable and will require that additional isolation measures be taken. Re-evaluation of installed VHF transceiver performance is not necessary if the filter insertion loss is 2 dB or less.
b. Evaluate the following VHF frequencies (25 kHz channels):
121.150 MHz
121.200 MHz
131.275 MHz
121.175 MHz
131.250 MHz
131.300 MHz
c. For VHF radios with 8.33 kHz channel spacing, evaluate the following additional VHF frequencies:
121.185 MHz 121.190 MHz
130.285 MHz 131.290 MHz
d. For installations on rotorcraft, ensure that the rotor blades do not interfere with the received signals. This problem has been experienced in some rotorcraft and varies with the rotation rate.
21-1.2 Antenna to Aircraft Navigation Reference Offset.
RTCA/DO-229D, Change 1, paragraph 2.2.4.3.3 (Class Gamma equipment) and RTCA/DO-253C, paragraph 2.3.11.5.1 stipulates the equipment will support installations with the ability to compensate for the navigation center to antenna offset. If applicable, confirm that the antenna to aircraft center of navigation offset is appropriate to the installation for GPS/SBAS or GPS/GBAS equipment supporting LPV or GLS approach capability.
Note: The fact that the GNSS antenna is top-mounted can result in several feet of vertical difference between the antenna and the aircraft center of navigation, significantly larger than for ILS antennas. The center-of-navigation to wheel-crossing height should be evaluated for each installation. For most installations, a fixed vertical offset is adequate.