AC 20-138D

Advisory circular · Airworthiness Approval of Positioning and Navigation Systems

Approved
March 28, 2014
Last reviewed
June 28, 2017
Family
AC 20-138 · 5 versions
Revision
D
14 CFR parts
1, 3, 11, 14, 15, 16, 21, 23, 25, 27, 29, 43, 91, 97, 121, 125, 135

Guidance, not mandatory unless a rule or AD requires it. DRS record last changed October 23, 2026.

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Appendix 5 Sample Airplane/Rotorcraft Flight Manual (Continued) Installation Center/Repair Station Model XXX 123 Fourth Street Navigation System Anytown, USA Table of Contents

SectionPage

1 General.............................................< > 2 Limitations........................................< > 3 Emergency/Abnormal Procedures....< > 4 Normal Procedures...........................< > 5 Performance......................................< > 6 Weight and Balance..........................< > 7 System Description...........................< > FAA Approved Page <> of <> Date: ________ A5-3

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Appendix 5 Sample Airplane/Rotorcraft Flight Manual (Continued) Installation Center/Repair Station Model XXX 123 Fourth Street Navigation System Anytown, USA SECTION 1 - GENERAL <Include the appropriate statement to describe the equipment capability:> TSO-C115<revision b or later>: The installed ABC system complies with AC 20-138D for IFR navigation using multi-sensor inputs including GPS for enroute, terminal area, and approach RNP operations (as appropriate). <include appropriate GPS TSO statement below as applicable> GPS TSO-C129<appropriate revision>: The installed ABC system complies with AC 20-138D for IFR navigation using GPS for enroute, terminal area, and non-precision approach operations. Non-precision approach operations include those based on conventional navigation aids with “or GPS” in the title and those with “GPS” and “RNAV(GPS)” in the title to “LNAV” minimums.

GPS/SBAS TSO-C145 or C146<appropriate revision> Class 3: The installed ABC equipment complies with AC 20-138D for navigation using GPS and GPS/SBAS (within the coverage of a satellite-based augmentation system complying with ICAO Annex 10) for enroute, terminal area, non-precision approach, and approach procedures with vertical guidance operations.

Non-precision approach operations include those based on conventional navigation aids with “or GPS” in the title and those with “GPS” and “RNAV(GPS)” in the title to “LNAV” and “LP” minimums. Approach procedures with vertical guidance includes “RNAV(GPS) to “LNAV/VNAV” and “LPV” minimums.

Note 1: TSO-C145a/C146a Class 3 equipment is not required to perform LP approaches.

Note 2: Functional Class Delta equipment is an “ILS look-alike” that only provides LP/LPV capability on the final approach segment.

GPS/SBAS TSO-C145 or C146<appropriate revision> Class 2: The installed ABC equipment complies with AC 20-138D for navigation using GPS and GPS/SBAS (within the coverage of a satellite-based augmentation system complying with ICAO Annex 10) for enroute, terminal area, non-precision approach, and approach procedures with vertical guidance operations.

Non-precision approach operations include those based on conventional navigation aids with “or GPS” in the title and those with “GPS” and “RNAV(GPS)” in the title to “LNAV” FAA Approved Page <> of <> Date: ________ A5-4

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Appendix 5 Sample Airplane/Rotorcraft Flight Manual (Continued) Installation Center/Repair Station Model XXX 123 Fourth Street Navigation System Anytown, USA minimums. Approach procedures with vertical guidance includes “RNAV(GPS) to “LNAV/VNAV” minimums.

GPS/SBAS TSO-C145 or C146<appropriate revision Class 1: The installed ABC equipment complies with AC 20-138D for navigation using GPS and GPS/SBAS (within the coverage of a satellite-based augmentation system complying with ICAO Annex 10) for enroute, terminal area, and non-precision approach operations. Non-precision approach operations include those based on conventional navigation aids with “or GPS” in the title and those with “GPS” and “RNAV(GPS)” in the title to “LNAV” minimums.

GPS/GBAS TSO-C161<appropriate revision>: The installed ABC system complies with AC 20-138D for navigation using GPS and GPS/GBAS (within the coverage of a ground-based augmentation system complying with ICAO Annex 10) for GPS/GBAS precision approach procedures to “GLS” minimums.

GPS TSO-C196(AR): The installed ABC system complies with AC 20-138D for IFR navigation using GPS for enroute, terminal area, and non-precision approach operations. Non-precision approach operations include those based on conventional navigation aids with “or GPS” in the title and those with “GPS” and “RNAV(GPS)” in the title to “LNAV” minimums.

<The following statement applies to all types of GNSS stand-alone equipment>:

Navigation information is referenced to the WGS-84 reference system, and should only be used where the Aeronautical Information Publication (including electronic data and aeronautical charts) conform to WGS-84 or equivalent.

<For TSO-C129(AR), TSO-C145/C146(AR), and TSO-C196(AR) equipment that complies with the requirements in appendix 1 of this AC:> The ABC equipment as installed has been found to comply with the requirements for GPS oceanic/remote navigation, when used in conjunction with the ABC prediction program. This does not constitute an operational approval.

<For baro-VNAV equipment:> The ABC VNAV system has been demonstrated capable of and has been shown to meet the accuracy requirements of:

VFR/IFR enroute, terminal and approach (if applicable) VNAV operation within the conterminous U.S. and Alaska in accordance with the criteria in AC 20-138D.

FAA Approved Page <> of <> Date: ________ A5-5

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Appendix 5 Sample Airplane/Rotorcraft Flight Manual (Continued) Installation Center/Repair Station Model XXX 123 Fourth Street Navigation System Anytown, USA SECTION 2 - LIMITATIONS

1. The system must use at least software version <insert version identification> as the minimum version.

2. A valid and compatible database must be installed and contain current data.

<Limitation for TSO-C129(AR) and TSO-C196(AR) equipment:>

3. The aircraft must have other operational, approved navigation equipment installed appropriate to the operation.

<Limitation for all GNSS equipment:>

4. The TSO-C<insert number and revision> equipment has a performance limitation necessitating an alternate airport flight planning operational mitigation. In the U.S., refer to sections 1-1-17, 1-1-18, 1-2-3 and 5-4-5 in the Aeronautical Information Manual for specific operational guidance. In other states, refer to their operational guidance for RNAV(GNSS) approaches.

5. The ABC Model XXX Quick Reference Guide, P/N <insert part number>, dated <insert date> (or later appropriate revision) must be immediately available to the flight crew whenever navigation is predicated on the use of the system.

<Limitation for baro-VNAV equipment:>

6. The ABC Model XXX VNAV system Pilot’s Guide, P/N <insert part number>, dated <insert date> must be immediately available to the flight crew whenever navigation is predicated on the use of the system.

7. 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 stepdown fixes.

8. Minimum altitude for autopilot coupled VNAV operation is <insert number> feet above ground level.

9. <Specify any additional limitations applicable to the particular installation.> FAA Approved Page <> of <> Date: ________ A5-6

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Appendix 5 Sample Airplane/Rotorcraft Flight Manual (Continued) Installation Center/Repair Station Model XXX 123 Fourth Street Navigation System Anytown, USA SECTION 3 - EMERGENCY/ABNORMAL PROCEDURES

EMERGENCY PROCEDURES No change.

ABNORMAL PROCEDURES

1. If ABC Model XXX GPS navigation information is not available or invalid, use remaining operational navigation equipment as appropriate.

2. If loss of integrity monitoring message is displayed, revert to an alternate means of navigation appropriate to the route and phase of flight or periodically cross-check the GPS guidance to other, approved means of navigation.

<For baro-VNAV equipment:> If VNAV information is intermittent or lost, disengage VNAV and use the primary barometric altimeter for vertical guidance.

SECTION 4 - NORMAL PROCEDURES <For GPS equipment:>

1. Normal operating procedures are outlined in the ABC Model XXX GPS Pilot's Guide.

2. <Describe approach mode sequencing.>

3. System Annunciators <applicable to installations with external annunciators>

a. Waypoint - <describe each annunciator>

b. Message - <describe each annunciator>

c. Approach - <describe each annunciator>

d. <describe any other annunciators> FAA Approved Page <> of <> Date: ________ A5-7

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Appendix 5 Sample Airplane/Rotorcraft Flight Manual (Continued) Installation Center/Repair Station Model XXX 123 Fourth Street Navigation System Anytown, USA

4. System Switches <applicable to installations with external switches>

a. Nav/GPS - <describe switch use and function>

b. RMI Switch - <describe switch use and function>

c. <describe any other switches>

5. Pilot's Display <describe the pilot's GPS display(s)>

6. Flight Director/Autopilot Coupled Operation <describe the procedures for coupling GPS to the flight director and/or autopilot system(s)>

7. <include any other normal operating procedures necessary> <For baro-VNAV equipment:>

1. Normal operating procedures are outlined in the Pilot’s Guide, P/N <insert part number>, dated <insert date> (or later appropriate revision).

2. Describe each remote annunciator, such as: waypoint (WPT), message (MSG).

3. Describe the function and operation of the various switches used with the system.

4. Describe the pilot’s and copilot’s display (i.e., CDI, HSI, OBS, etc.)

5. Describe the coupling of VNAV system steering information to the autopilot and/or flight director.

SECTION 5 - PERFORMANCE No Change SECTION 6 - WEIGHT AND BALANCE <Refer to revised weight and balance data, if applicable.> SECTION 7 - SYSTEM DESCRIPTION

<Provide a brief description of the system, its operation, installation, etc.>

FAA Approved Page <> of <> Date: ________ A5-8

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Navigation Specification Operational Requirements/ Authorizations Required Equipment Reference Guidance Oceanic and Remote GNSS FDE availability Two <insert name> Meets the applicable Areas of Operation must be verified prior to installed systems, requirements of (formerly Class II flight. Maximum operating and receiving AC20-138D, Navigation). predicted FDE unavailability is 25 minutes.

No time limit using GNSS as the primary navigation sensor.

usable navigation information from each of the dual GNSS sensors (or one navigation system and one GNSS sensor for those routes requiring only one long range navigation sensor).

AC90-100A, AC91-70, FAA Order 8400.33.

This does not constitute an operational approval.

North Atlantic (NAT) GNSS FDE availability must be verified prior to Two <insert name> installed systems, Meets the applicable requirements of Minimum Navigation flight. Maximum operating and receiving AC20-138D, Performance predicted FDE usable navigation AC91-70, Specifications (MNPS) unavailability is 25 minutes.

No time limit using GNSS as the primary navigation sensor.

information from each of the dual GNSS sensors (or one FMS and one GNSS sensor for those routes requiring only one lon g range AC91-49.

This does not constitute an operational approval.

RNAV-10 GNSS FDE availability i ti )Two <insert name> Meets the applicable RNP-10 must be verified prior to flight. Maximum predicted FDE unavailability is 25 minutes.

EPU/ANP does not exceed RNP.

No time limit using GNSS as the primary installed systems, operating and receiving usable navigation information from each of the dual GNSS sensors.

requirements of AC20-138D FAA Order 8400.128.

This does not constitute an operational approval.

4/7/16 AC 20-138D Change 2 Appendix 5 A5-2. Sample AFM(S)/RFM(S) PBN Capabilities and Qualification Basis.

Section II Operating Limitations Model XXX

NAVIGATION OPERATIONAL CAPABILITIES The navigation equipment as installed has been found to comply with the requirements established for the following navigation specifications:

i ti (Continued Next Page) FAA Approved Page <> of <> Date: ________ A5-9

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Appendix 5

SECTION II - OPERATING LIMITATIONS MODEL XXX NAVIGATION OPERATIONAL CAPABILITIES (Continued) Navigation Specification Operational Requirements/ Authorizations Required Equipment Reference Guidance B-RNAV/RNAV-5 EPU/ANP does not At least one <insert Meets the applicable RNP-5. exceed RNP. name> installed system requirements of is receiving usable AC20-138D, No time limit using navigation information AC90-96A, GNSS as the primary from one or more of the AC90-100A, navigation sensor. following sensors: EASA AMC 20-4.

1. Multiple DMEs, or

2. GNSS sensor.

RNP-4 Oceanic and GNSS FDE availability Two <insert name> Meets the applicable Remote Area must be verified prior to installed RNP navigation requirements of Operations. flight. Maximum predicted FDE unavailability is 25 minutes.

EPU/ANP does not exceed RNP.

No time limit using GNSS as the primary navigation sensor.

systems, operating and receiving usable navigation information from each of the dual GNSS sensors.

AC20-138D, FAA Order 8400.33.

This does not constitute an operational approval.

RNAV-2 GNSS is required for At le ast one <insert Meets the applicable RNAV-1 takeoff in P-RNAV name> installed system requirements of P-RNAV airspace. is receiving usable AC20-138D, RNAV Routes (DPs, STARS, Q and T Routes) GNSS FDE availability must be verified prior to flight for DPs that navigation information from one or more of the following sensors:

AC90-105, AC90-96A, AC90-100A, JAA TGL 10.

RNP-2 require GNSS. 1. Multiple DMEs, or RNP-1 EPU/ANP does not exceed RNP.

2. GNSS sensor (required for takeoff in P-RNAV airspace and some DPs).

This does not constitute an operational approval.

No time limit using GNSS as the primary navigation sensor.

(Continued Next Page) FAA Approved Page <> of <> Date: ________ A5-10

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Appendix 5

SECTION II - OPERATING LIMITATIONS MODEL XXX NAVIGATION OPERATIONAL CAPABILITIES (Continued) Navigation Specification Operational Requirements/ Authorizations Required Equipment Reference Guidance RNP-APCH [titled All instrument approach At least one <insert Meets the applicable RNAV (GPS) or RNAV procedures that are name> installed system requirements of, (GNSS)] retrieved from the is receiving usable AC20-138D, -including RNP navigation system navigation information AC90-105, procedures to a database are authorized. from a GNSS sensor EASA AMC 20-27.

minimum value of RNP-0.3 (LNAV minimums) <include LPV minimums if GNSS is required to initiate RNAV (GPS) approach procedures.

(required for RNAV (GPS) approach procedures) This does not constitute an operational approval.

appropriate>. For RNAV(GPS) approach procedures, a RNP AR-APCH missed approach is procedures, and required if both GNSS approach procedures sensors become with RF legs are NOT unavailable authorized. EPU/ANP does not <Include a separate entry if RNP AR-APCH or advanced RNP capability such as RF exceed RNP (except during a missed approach procedure following loss of GNSS navigation).

legs ARE approved.> Maximum predicted RAIM outage is 5 minutes.

For IL S, LOC, LOC-BC, LOA, and SDF approach procedures, the active navigation source must be LOC or BC (green needles) prior to crossing the final approach fix.

Enroute, Terminal and Use of Vertical Glidepath The selected navigation Meets the applicable Approach Vertical (GP) guidance to a system is receiving requirements of Navigation (VNAV) published DA is approved. usable information for a baro-VNAV (or SBAS, if applicable) solution.

AC20-138D, AC90-100A, AC90-105, EASA AMC 20-27.

FAA Approved Page <> of <> Date: ________ A5-11

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Appendix 6 Appendix 6. Installation of GNSS Equipment for VFR Use Only.

A6-1. I ntroduction.

This appendix provides guidelines for the installation of stand-alone GNSS systems used for VFR navigation only.

A6-2. General.

GNSS equipment may be installed on a no-hazard basis as a supplement to VFR navigation.

Such installations need only to verify that the GNSS installation does not introduce a hazard to the aircraft (e.g., properly secured for crashworthiness, not combustible, etc) including EMI/EMC. Loss of or misleading VFR navigation information is considered a minor hazard failure condition; therefore, it is acceptable to have development assurance level D for software per RTCA/DO-178B or ‘C’, and electronic hardware, per RTCA/DO-254. A readable placard must be installed in clear view of the pilot stating that the equipment is only to be used for VFR operations, unless the equipment automatically displays this message on start-up and pilot action is required to clear the message. An AFMS/RFMS is not required since the placard or display contains the equipment limitation.

A6-3. Applicability.

This appendix applies to all un-pressurized aircraft less than 6000 pounds where the modification is classified as a minor alteration.

A6-4. Technical Instructions.

Install the GPS as follows:

a. The GPS equipment should be located in a position which is viewable and accessible to the pilot from his/her normally seated position. The installed GPS equipment should not:

(1) Restrict access to or view of any control, display or indicator;

(2) Restrict movement of the flight controls;

(3) Interfere with the pilot’s vision along the flight path; or

(4) Restrict pilot/passenger egress.

b. The installation should be carried out in accordance with the equipment manufacturer’s installation manual/instructions, the aircraft maintenance manual and the guidelines in AC 43.13-2 (latest revision). The installation should conform to the following requirements:

(1) Equipment manufacturer-supplied or standard parts should be used.

A6-1

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(2) If a ‘non-standard’ method of installation is used, the equipment manufacturer’s recommended procedures should be followed.

(3) The GPS mounting should be tested to ensure that it will be restrained throughout the flight envelope.

(4) Where a modification is required to the aircraft structure to show compliance with paragraph A6-4.b(3) of this appendix, the modification is to be carried out in accordance with the aircraft maintenance manual and the guidelines in the latest revisions of AC 43.13-1 and AC 43.14-2.

c. If required, install a remote GPS antenna as follows:

(1) Determine a suitable location for the GPS antenna on the upper fuselage.

Particular care should be taken to ensure that at least the minimum separation is maintained between the GPS antenna and VHF communications and ELT antennas.

(2) Install the equipment manufacturer-approved GPS antenna in accordance with the equipment manufacturer’s installation manual/instructions, the aircraft maintenance manual and the guidelines in AC 43.13-2 (latest revision). The GPS antenna installation should be tested to ensure that it would be restrained throughout the flight envelope.

(3) If using an internally mounted, equipment manufacturer-supplied remote antenna, install the antenna in accordance with the equipment manufacturer’s installation manual/instructions. Ensure that the antenna and associated cable will not interfere with pilot’s vision, aircraft controls or displays, or pilot/passenger egress.

d. Install and placard an appropriately rated circuit breaker or fuse.

e. If required, install a remote GPS indicator as follows:

(1) Determine a suitable location for the GPS indicator. The indicator should be located in the instrument panel and readily viewable to the pilot from his/her normally seated position.

(2) Install the indicator in accordance with the equipment manufacturer’s installation manual/instructions, the aircraft maintenance manual and the guidelines in AC

43.13-2 (latest revision).

(3) Interconnect the GPS, power supply, indicator and antenna (as required) in accordance with the equipment manufacturer’s installation manual/instructions.

f. Unless the equipment automatically displays a message on start-up and pilot action is required to clear the message, install the following placard in the vicinity of the GPS and in clear view of the pilot: GPS APPROVED FOR VFR USE ONLY.

A6-2

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g. Close the GPS circuit breaker or install the fuse.

h. Carry out a functional test of the GPS installation in accordance with the equipment manufacturer’s installation/operation instructions. Checks are also to be carried out to determine satisfactory operation of all disturbed systems, that there is no interference between GPS and other systems, no effect on the aircraft compass system and that there is no interference with the aircraft flight controls.

A6-3