7 Chapter 3. ADS-B System Installation Guidance
3-1. General Installation Guidance.
a. Environmental qualification. Ensure the environmental qualification of the installed equipment is appropriate for the aircraft in accordance with AC 21-16G, RTCA/DO-160 Versions D, E, F, and G “Environmental Conditions and Test Procedures for Airborne Equipment.”
b. System Safety assessment. The ADS-B System Design Assurance (SDA) parameter indicates the probability of an ADS-B system malfunction causing false or misleading position information or position quality metrics to be transmitted. SDA may be preset at installation for systems that do not utilize multiple position sources with different design assurance levels, otherwise the system must be capable of adjusting the SDA broadcast parameter to match the position source being employed at the time of transmission.
(1) Compliant architecture. ADS-B equipment meeting the minimum performance requirements of TSO-C166b or TSO-C154c that is directly connected to a position source meeting the minimum performance requirements of any revision of TSO-C129, Airborne Supplemental Navigation Equipment Using the Global Positioning System (GPS), TSO-C145, Airborne Navigation Sensors Using the Global Positioning System (GPS) Augmented by the Wide Area Augmentation System (WAAS), TSO-C146, Stand-Alone Airborne Navigation Equipment Using the Global Positioning System (GPS) Augmented by the Wide Area Augmentation System (WAAS), or TSO-C196, Airborne Supplemental Navigation Sensors for Global Positioning System Equipment Using Aircraft-Based Augmentation, may set the SDA = 2 without further analysis. For installations in aircraft with more complex system architectures, a system safety assessment, as described below, is required to set the SDA. Installations with uncertified equipment must set SDA = 0.
(2) Conducting the system safety assessment. ADS-B systems using position sources not listed in paragraph 3-1b(1) or systems with intermediary devices such as data concentrators must accomplish a system safety assessment and set the SDA according to the results of the assessment. Systems integrated through a highly integrated data bus architecture must complete the system safety assessment. The system safety assessment must demonstrate that the installed system meets all TSO-C166b or TSO-C154c requirements to set the SDA = 2 or 3. This can be accomplished using the methods, for example, as described in AC 25.1309-1(), Systems Design and Analysis, AC 23.1309-1(), System Safety Analysis and Assessment for Part 23 Airplanes, SAE ARP 4761, Guidelines and Methods for Conducting the Safety Assessment Process on Civil Airborne Systems and Equipment, or SAE ARP 4754a, Certification Considerations for Highly- Integrated or Complex Aircraft Systems.
Note: Although the direct effects to your aircraft of an ADS-B failure may be minor, the ADS-B information will be used by other ADS-B equipped aircraft and by ATC, thus the provisions in AC 23.1309-1() that allow reduction in failure probabilities and design assurance level for aircraft under 6,000 pounds do not apply to the ADS-B system.
8 If the system contains different design assurance levels for hardware and software, then the worst case design assurance level should be used. For example, if the hardware assurance level is level C, and the software assurance level is B, the SDA would indicate that the system has been qualified commensurate with a Major failure condition. If the ADS-B system is integrated with a non-compliant GPS, the SDA must be set to 0.
(3) Existing equipment design assurance. The aircraft installation may make use of some equipment certified for use with an existing transponder system. There is no intent for this safety assessment to drive the replacement of existing altimetry, flight crew controls, heading instruments, or antennas. In contrast, the position source installation must be compliant with the guidance in this AC including design assurance considerations.
c. Position latency. Latency is the difference between the time a measurement is taken to determine the aircraft’s geometric position and the time when that position measurement is transmitted by the aircraft’s ADS-B equipment. Limiting the latency in ADS-B systems minimizes the errors in the reported position. TSO-C166b and TSO-C154c ADS-B equipment typically compensate for latency by extrapolating the position based on velocity information. All applicants must demonstrate compliance with the latency requirements in paragraph 3-1c(1). This can be done by equipping with a compliant architecture listed in paragraph 3-1c(2) or performing an analysis detailed in paragraph 3-1c(3). Latency terms are further defined in appendix 3 of this AC.
Note: To demonstrate compliance with 14 CFR 91.227 you must calculate latency from the position source time of measurement (TOM). Do not calculate latency from the position source time of applicability, as defined in DO-260B, Minimum Operational Performance Standards for 1090 MHz Automatic Dependent Surveillance-Broadcast (ADS-B), with Corrigendum 1 and DO-282B with corrigendum 1.
(1) Position latency requirements. There are two position latency requirements associated with ADS-B OUT.
(a) Total latency. Total latency is defined as the difference between the time when the position is measured and when the position is transmitted from the aircraft. In order to meet 14 CFR 91.227, the total latency must be less than or equal to 2.0 seconds.
(b) Uncompensated latency. Uncompensated latency is the difference between the time of applicability for the transmitted position and the actual time the position is transmitted from the ADS-B system. In order to meet 14 CFR 91.227, the uncompensated latency must be less than or equal to 0.6 seconds. The aircraft must compensate for any latency greater than 0.6 seconds but must not overcompensate by more 0.2 seconds (i.e. lead the aircraft position).
Note: RTCA Special Committee 186 recommends ADS-B OUT systems transmit position information with an uncompensated latency of less than or equal to 0.4 seconds. This recommendation is to support future ADS-B IN applications. The 14 CFR 91.227 latency requirements support ATC separation services and the initial basic ADS-B IN applications. However, we encourage you to minimize
9 uncompensated latency as much as possible in your installation. Recommendations for minimizing latency are included in appendix 3 of this AC.
(2) Compliant architecture. ADS-B systems which directly connect a position source meeting the minimum performance requirements of any revision of TSO-C145, TSO-C146, or TSO-C196 with ADS-B equipment meeting the minimum performance requirements of TSO-C166b or TSO-C154c meet the total latency and uncompensated latency requirements. Systems with a compliant architecture do not need to accomplish a position and velocity latency analysis.
(3) Position latency analysis. If you are installing an ADS-B system that does not have a compliant architecture described in paragraph 3-1c(2), you must accomplish a latency analysis to demonstrate that the installed ADS-B system meets the total latency and uncompensated latency requirements. Systems integrated through a highly integrated data bus architecture must complete the latency analysis. Appendix 3 of this AC provides for an acceptable method to complete the latency analysis.
d. Integrity metric latency. There is an allowance for Global Navigation Satellite System (GNSS) position sources to delay the update of the integrity containment radius while attempting to detect and exclude faulted satellites. 14 CFR 91.227 allows up to 12 seconds for the ADS-B system to transmit a change in the Navigation Integrity Category (NIC). This 12 second allowance is available for any position source, not just GNSS position sources. The 12 seconds includes both the time for the position source to detect the fault and time for the ADS-B system to transmit the fault indication. The requirement to indicate a change in NIC applies to the time between when a faulted position is first transmitted and when the updated NIC is transmitted indicating the fault. The total time to update the NIC is based on the cumulative effect of: (1) the position source fault detection and exclusion time; and (2) the worst-case asynchronous transmission difference between when the faulted position is transmitted and when the NIC indicating the fault is transmitted.
(1) Compliant architecture. ADS-B equipment meeting the minimum performance requirements of TSO-C166b or TSO-C154c that are directly connected to a position source meeting the minimum performance requirements of any revision of TSO-C145, TSO-C146, or TSO-C196 will typically meet the integrity latency requirements. For these systems you only need to demonstrate, through analysis, that a non-isolated GNSS satellite fault detected by the position source is properly passed to the ADS-B equipment and that the ADS-B equipment indicates an invalid position by transmitting the position integrity and accuracy metrics equal to zero.
Note: GNSS Sensor ARINC Characteristic 743A-5, allows flexibility in how information is transferred during a GNSS satellite fault, thus it is necessary to ensure a non-isolated satellite failure results in the ADS-B indicating an invalid position.
(2) Integrity metric latency analysis. If you are installing an ADS-B system without a compliant architecture described above, you must accomplish a latency analysis to demonstrate the ADS-B system meets the integrity metric latency requirements. The latency analysis should include the maximum time for a position source to indicate an integrity fault, any delay added by an intermediary device such as a data concentrator, and the delay added by the ADS-B equipment.
e. System design assurance (SDA) and source integrity level (SIL) latency.
14 CFR 91.227 requires changes in the SDA or SIL be broadcast within 10 seconds. Changes in the SDA or SIL will typically only occur when a secondary position source is integrated into an ADS-B system and that secondary position source has a different SDA or SIL than the primary position source. If you integrate multiple position sources with different SDAs or SILs, demonstrate during ground testing that a change in position source results in an updated SDA and SIL within 10 seconds. If integrating an ADS-B transmitter with a non-compliant GPS, the SDA and SIL must be set to 0.
f. Populating message elements. 14 CFR 91.227 lists parameters that must be populated
(i.e. not a null value) for operation in airspace defined by 14 CFR 91.225. All parameters transmitted by the ADS-B system must conform to the standards in TSO-C166b or TSO-C154c and may not contain false or misleading information.
3-2. ADS-B Equipment.
a. Equipment eligibility. ADS-B equipment must meet the requirements specified in TSO-C166b or TSO-C154c.
b. Installation guidance.
(1) UAT systems with Mode S transponders. Do not install a UAT ADS-B OUT system which has the capability to transmit a random 24-bit address in an aircraft which also has a Mode S transponder unless the random 24-bit feature is disabled. The ATC automation system would interpret the different 24-bit addresses as two separate aircraft, and alert controllers to a conflict that does not actually exist.
(2) Mixed transmit/receive classifications. TSO-C166b and TSO-C154c allow Class A transmit-only and Class A receive-only equipment configurations. There are no restrictions for installing a certain class of receive equipment with a different class of transmit equipment.
For example, a Class A3 transmit-only unit can be used in the same aircraft with a Class A1 receive-only unit. It is also acceptable to have a TSO-C166b transmitter and a TSO-C154c receiver and vice versa.
(3) Stand alone 1090ES transmitters. RTCA/DO-260B, paragraph 2.2.2.2 only allows Class A0 and B0 1090ES stand-alone (not integrated with a transponder) transmitters.
This AC does not cover installation approval for class A0 or B0 1090ES transmitters because they are not compliant with 14 CFR 91.227.
(4) Multiple ADS-B OUT systems. If the aircraft has the ability to operate a 1090ES and a UAT ADS-B OUT system at the same time, the systems must have a single point of entry for the emergency code, IDENT, and Mode 3/A code. Neither system may use a random address feature. If dual ADS-B OUT systems of the same link are installed (e.g., to increase dispatch reliability), the installation must preclude operation of both systems simultaneously.
11 Note: 1: We recommend that you do not install both 1090ES and UAT ADS-B OUT capability on the same aircraft.
Note: 2: Installation of dual 1090ES and UAT ADS-B IN capability is acceptable and encouraged.
c. Configuration of associated parameters. The following paragraphs provide additional guidance on setting key ADS-B OUT parameters. Definitions for each of the following associated parameters are included in appendix 1.
(1) International Civil Aviation Organization (ICAO) 24-bit address. You must set the ICAO 24-bit address during installation in accordance with the ADS-B equipment manufacturer’s instructions. For U.S. civil aircraft, the ICAO 24-bit address is established as a function of the aircraft’s registration or “N” number. You can determine the appropriate address for U.S. registered aircraft on the following FAA website: http://registry.faa.gov/aircraftinquiry/.
Use of a random 24 bit address is discussed further in paragraph 3-7.b.(3) of this AC.
Note: 1: The ICAO 24-bit address is also used by the Mode S transponder. For the addition of ADS-B (1090ES) in an existing Mode S transponder installation, verify that the ICAO 24-bit address decodes to the current aircraft registration number.
Note: 2: The ICAO 24-bit address will have to be updated if the aircraft’s registration number changes.
(2) Aircraft length and width. This parameter must be configured during installation.
Do not set the length and width parameter to a value of “0”, as the length and width code is required by 14 CFR 91.227. The length and width code chosen should be the smallest value that encompasses the entire aircraft. For example, the length and width code for a helicopter with a refueling boom would include the rotor blades or any other fixed object that extends from the fuselage, see figure 2.
12 Figure 2. Example of Aircraft Length and Width Code Determination.
Reported Length (using next higher value) Reported Width (using next higher value) Actual length of aircraft Actual width of aircraft Aerial Refueling boom GNSS antenna location
(3) ADS-B IN capability. This parameter must be configured to indicate if the aircraft has an ADS-B IN system installed. For ease of installation, the parameter does not have to indicate the operational status of the ADS-B IN system. If the aircraft has both 1090ES ADS-B IN and UAT ADS-B IN systems installed, both the 1090ES ADS-B IN and UAT ADS-B IN capability should be set accordingly.
(4) Emitter category. Table 1, Emitter Category, provides guidance on setting the emitter category.
13 Table 1. Emitter Category
Emitter Category Description No Emitter Category Do not use this emitter category. If no emitter category fits your installation, seek guidance from the FAA as appropriate.
Light Airplane < 15,500 pounds Any airplane with a maximum takeoff weight less than 15,500 pounds. This includes very light aircraft (light sport aircraft) that do not meet the requirements of 14 CFR 103.1.
Small Airplane ≥ 15,500 to < 75,000 pounds Any airplane with a maximum takeoff weight greater than or equal to15,500 pounds but less than 75,000 pounds.
Large Airplane ≥ 75,000 to < 300,000 pounds Any airplane with a maximum takeoff weight greater than or equal to 75,000 pounds but less than 300,000 pounds that does not qualify for the high vortex category.
Large Airplane with High Vortex Any airplane with a maximum takeoff weight greater than or equal to 75,000 pounds but less than 300,000 pounds that has been determined to generate a high wake vortex. Currently, the Boeing 757 is the only example.
Heavy Airplane ≥ 300,000 pounds Any airplane with a maximum takeoff weight equal to or above 300,000 pounds.
Highly Maneuverable > 5 G and > 400 TAS Any airplane, regardless of weight, which can maneuver in excess of 5 G’s and maintain true airspeed above 400 knots.
Rotorcraft Any rotorcraft regardless of weight.
Glider / Sailplane Any glider or sailplane regardless of weight.
Lighter than Air Any lighter than air (airship or balloon) regardless of weight.
UAV Any unmanned aerial vehicle or unmanned aircraft system regardless of weight.
Ultralight Vehicle A vehicle that m eets the requirements of 14 CFR 103.1.
Light sport aircraft should not use the ultralight emitter category unless they meet 14 CFR 103.1.
3-3. Position Source.
a. Equipment eligibility. 14 CFR 91.227 is performance based and does not require any specific position source. The existing navigation equipment and airworthiness standards should be used, however they must be augmented to address the unique issues associated with ADS-B. A TSO authorization alone is not sufficient to ensure ADS-B compatibility. The position source must also comply with the appendix 2 minimum performance requirements. Compliance with the appendix 2 requirements may be documented in the position source manufacturer’s installation instructions.
Note: Not all GNSS position sources will provide the same availability. See appendix 2 for more information on GNSS availability. The FAA recommends TSO-C145 or TSO-C146 position sources that meet the appendix 2 requirements to maximize availability and ensure access to the airspace identified in 14 CFR 91.227 after January 1, 2020.
b. Installation guidance.
(1) Installation guidance. The position source must be installed in accordance with the applicable guidance. New GNSS position sources must be installed in accordance with AC 20-138C, Airworthiness Approval of Positioning and Navigation Systems.
(2) Position source and ADS-B equipment interface. Unless the ADS-B equipment manufacturer has analyzed the interface between the position source and the ADS-B equipment you are installing, and specifically listed the position source in the ADS-B equipment’s installation manual, you must provide an analysis of the interface between the position source and the ADS-B equipment which demonstrates that the position, velocity, position accuracy, position integrity, and velocity accuracy information taken from the position source is properly interpreted by the ADS-B equipment. When installing modifications to a position source, the installer must determine and test those portions of the ADS-B system that are impacted by the modification and ensure the ADS-B system is not adversely impacted.
Note: This analysis will require engineering design data from the ADS-B equipment manufacturer and / or the position source manufacturer.
(3) Secondary position source. There is no requirement to have a secondary position source input. However, if you interface a secondary position source to the ADS-B system, it must meet the requirements in appendix 2.
Note: If a position source is unable to provide 14 CFR 91.227 accuracy and integrity values, it will not qualify the aircraft to operate in airspace defined by 14 CFR 91.225 after January 1, 2020.
(4) Position source selection. If multiple position sources are interfaced to the ADS-B equipment, source selection can be accomplished manually by the pilot, automatically by the aircraft’s navigation system, or by the ADS-B equipment. We discourage automatic selection of the ADS-B position source based solely on the navigation source in use because operational requirements sometimes dictate a navigation source that may not provide the best ADS-B performance. If the ADS-B equipment accomplishes the position source selection, it should do so in accordance with TSO-C166b or TSO-C154c. If multiple sources are interfaced to the ADS-B system, there should be a means for the flight crew to readily determine which source is selected. Describing how this selection is performed in the AFM is one acceptable means of compliance.
Note: TSO-C166b and TSO-C154c require the ADS-B equipment to use a single position source for the latitude, longitude, horizontal velocity, and accuracy metrics, and integrity metrics.
(5) Position source. The ADS-B position source does not need to be the same position source used for navigation. It is acceptable for a GNSS position source to be embedded in the ADS-B equipment and provide position information to the ADS-B without providing any navigation information to other on-board systems. As addressed in appendix 2, an integrated GNSS position source should still meet the requirements of TSO-C145, TSO-C146, or
15 TSO-C196.
(6) GPS / UAT time mark synchronization. When integrating a UAT with an external GPS, the design of the hardware time mark must be interoperable. Some GPS synchronize the leading edge of the time mark to the UTC second. Other GPS let the time mark pulse be asynchronous to the UTC second and then record the time of the leading edge in the digital data along with the position solution. The UAT equipment must support the GPS time mark design. If the UAT equipment and GPS do not share a common time mark design, the UAT equipment will not be properly synchronized with the ground system and other aircraft.
c. Configuration of associated parameters. The following paragraphs provide additional guidance on setting key ADS-B OUT parameters. Definitions for each of the following associated parameters are included in appendix 1.
(1) Latitude and longitude. The ADS-B equipment must set the latitude and longitude based on the real-time position information provided by the position source.
(2) Horizontal velocity. The ADS-B equipment must set the horizontal velocity based on the real-time velocity information provided by the position source. The ADS-B equipment must transmit a north/south east/west velocity while airborne and a combination of ground speed and ground track or heading while on the surface. Ensure the position source provides horizontal velocity in both formats or ensure the ADS-B equipment can properly convert between formats.
We recommend transmitting heading instead of ground track while on the surface, see paragraph 3-5c for additional information on interfacing heading.
(3) Source Integrity Level (SIL). SIL is typically a static (unchanging) value and may be set at the time of installation if a single type of position source is integrated with the ADS-B system.
SIL is based solely on the position source’s probability of exceeding the reported integrity value and should be set based on design data from the position source equipment manufacturer. Installations which derive SIL from GNSS position sources compliant with any revision of TSO-C129, TSO-C145, TSO-C146, or TSO-C196 which output Horizontal Protection Level (HPL) or Horizontal Integrity Level (HIL) should set the SIL = 3 because HPL and HIL are based on a probability of 1x10-7 per hour. Do not base NIC or SIL on Horizontal Uncertainty Level (HUL) information. If integrating with a non-compliant GPS, SIL must be set to 0.
(4) Source Integrity Level Supplement (SILSUPP). SILSUPP is based on whether the position source probability of exceeding the reported integrity value is calculated on a per hour or per sample basis and should be set based on design data from the position source equipment manufacturer. ADS-B systems interfaced with a GNSS position source compliant with any revision of TSO-C129, TSO-C145, TSO-C146, or TSO-C196 may preset SILSUPP to ZERO, as GNSS position sources use a per hour basis for integrity.
(5) Navigation Integrity Category (NIC). The ADS-B equipment must set the NIC based on the real-time integrity metric provided by the position source. When interfacing GNSS position sources, the NIC should be based on the HPL or HIL. However, while HPL values significantly smaller than 0.1 nm can be output from single frequency GNSS sources, the HPL
16 may not actually achieve the reported level of protection as there are error contributions that are no longer considered negligible. You should review the position source design data to determine if all error sources are taken into consideration, or if the position source limits the HPL output, when computing an un-augmented Receiver Autonomous Integrity Monitoring (RAIM) based HPL. This applies to all TSO-C129 and TSO-C196 position sources, and to TSO-C145 and TSO-C146 position sources when operating in un-augmented modes where the HPL is based on RAIM. This may apply to some position sources even when operating in an augmented mode. If the position source does not account for all errors or accomplish the appropriate HPL limiting, you must ensure you interface the position source to ADS-B equipment which limits the NIC ≤ 8. See appendix 2, paragraph 4.f for additional information on HPL considerations.
(6) Navigation Accuracy Category for Position (NACP). The ADS-B equipment must set the NACP based on the real time 95% accuracy metric provided by the position source.
When interfacing GNSS sources, the NACP should be based on a qualified Horizontal Figure of Merit (HFOM).
(7) Navigation Accuracy Category for Velocity (NACV). Set the NACV based on design data provided by the position source manufacturer. The NACV may be updated dynamically from the position source, or set statically based on qualification of the position source.
(a) A NACV = 1 (< 10 m/s) may be permanently set at installation for GNSS equipment passing the tests identified in appendix 2, or may be set dynamically from velocity accuracy output of a position source qualified in accordance with the appendix 2 guidance.
(b) A NACV = 2 (< 3 m/s) may be set dynamically from velocity accuracy output of a position source qualified in accordance with the appendix 2 guidance. Do not permanently preset a NACV = 2 at installation, even if the position source has passed the tests identified in appendix 2.
(c) A NACV = 3 or NACV = 4 should not be set based on GNSS velocity accuracy unless you can demonstrate to the FAA that the velocity accuracy actually meets the requirement.
(8) Geometric Altitude. Ensure that the geometric altitude provided by the position source is based on Height-Above-Ellipsoid (HAE) instead of Height-Above-Geoid (HAG). Do not interface a position source that provides HAG or Mean Sea Level (MSL) altitude to the ADS-B equipment unless the ADS-B equipment has the ability to determine the difference between an HAG and HAE input, and that the ADS-B equipment has demonstrated during design approval that it can properly convert HAG to HAE using the same model as the position source. It would also be acceptable to demonstrate that the error due to conversion of HAG to HAE does not cause the reported geometric accuracy to be exceeded.
(9) Geometric Vertical Accuracy (GVA). Set the GVA based on design data provided by the position source manufacturer. GNSS position sources may provide the geometric altitude
17 accuracy through the Vertical Figure of Merit (VFOM). If the position source does not output a qualified vertical accuracy metric, the GVA parameter should be set to “0.”
(10) Ground Track Angle. For installations that do not have heading information available, ground track from the position source must be transmitted while on the surface. Many position sources will provide accurate ground track information, but the ground track may only be accurate above certain ground speeds. If the position source ground track is inaccurate below a certain ground speed and the position source does not inhibit output of the ground track at these slower speeds, the installer should ensure that the ADS-B equipment has the capability to invalidate the ground track when the GNSS ground speed falls below 7 knots. Erroneous ground track readings could be misleading for ATC surface operations and ADS-B IN applications. If the position source itself inhibits output of ground track at slower speeds where the ground track would be inaccurate, the installer may interface the position source ground track to the ADS-B equipment without any restrictions.
3-4. Barometric Altitude Source.
a. Equipment eligibility.
(1) Utilize barometric altitude from a barometric altimeter meeting the minimum performance requirements of:
(a) TSO-C10, Altimeter, Pressure Actuated, Sensitive Type, (any revision) or
(b) TSO-C106, Air Data Computer (any revision).
(2) If appropriate, utilize a digitizer meeting the minimum performance requirements of any revision of TSO-C88, Automatic Pressure Altitude Reporting Code-Generating Equipment.
b. Installation guidance.
(1) The barometric altitude used for the ADS-B broadcast must be from the same altitude source as the barometric altitude used for the ATC transponder Mode C reply, if an altitude-encoding transponder is installed in the aircraft.
(2) 14 CFR 91.225 and 91.227 do not alter any existing regulatory guidance regarding the barometric altitude accuracy or resolution. For example, if an operation requires a 25 foot altitude resolution or a 14 CFR part 91 appendix G, Operations in Reduced Vertical Separation Minimum (RVSM), accuracy, that resolution and accuracy should be reflected in the ADS-B message.
(3) If a secondary altitude source is utilized when a secondary transponder is selected or a secondary altitude source is selected for a single transponder, the altitude source for ADS-B must also be changed so that the altitude source remains the same for both the transponder and ADS-B.
c. Configuration of associated parameters. The following paragraphs provide additional guidance on setting key ADS-B OUT parameters. Definitions for each of the following associated parameters are included in appendix 1.
(1) Barometric altitude. The ADS-B equipment must update the barometric altitude based on the real-time barometric altitude provided by the barometric altitude source.
(2) Barometric Altitude Integrity Code (NICBARO). You should verify the type of altitude source installed in the aircraft and interface the altitude system per the ADS-B equipment manufacturer’s instructions. For aircraft with an approved, non-Gillham altitude source, NICBARO should be preset at installation to ONE. For aircraft with a Gillham altitude source without an automatic cross-check, NICBARO must be preset at installation to ZERO. For aircraft which dynamically cross-check a Gillham altitude source with a second altitude source the NICBARO must be set based on the result of this cross-check. We recommend that ADS-B installations use non-Gillham altitude encoders to reduce the potential for altitude errors.
3-5. Heading Source.
a. Equipment eligibility. For installations that integrate heading on the airport surface, the heading source must meet the minimum performance requirements of any revision of TSO-C5, Direction Instrument, Non-Magnetic (Gyroscopically Stabilized), or any revision of TSO-C6, Direction Instrument, Magnetic (Gyroscopically Stabilized). The equipment must have the appropriate installation and airworthiness approval.
b. Installation guidance.
(1) The heading does not need to come from the same source as the position and velocity.
(2) Interfacing heading is not required, but highly encouraged if the aircraft has an approved heading source.
c. Configuration of associated parameters. When the aircraft is on the surface, the ADS-B system is required to transmit either heading or ground track, however we recommend transmitting heading if a source of heading information is available and valid. True heading is preferred, but magnetic heading is acceptable. Ensure the heading type (true or magnetic) interfaced to the ADS-B equipment matches the heading type transmitted from the ADS-B equipment.
3-6. TCAS Status Source.
a. Equipment eligibility. TCAS II systems should comply with TSO-C119a, Traffic Alert and Collision Avoidance System (TCAS) Airborne Equipment, or subsequent, and be installed in accordance with AC 20-131A, Airworthiness Approval of Traffic Alert and Collision Avoidance Systems (TCAS II) and Mode S Transponders, or any revision of AC 20-151, Airworthiness Approval of Traffic Alert and Collision Avoidance Systems (TCAS II) Versions 7.0 and 7.1 and Associated