8 CHAPTER 3. ADS-B OUT SYSTEM INSTALLATION GUIDANCE
3.1 General Installation Guidance.
3.1.1 Environmental Qualification.
Ensure the environmental qualification of the installed equipment is appropriate for the aircraft in accordance with AC 21-16G, RTCA Document DO-160 versions D, E, F, and G, “Environmental Conditions and Test Procedures for Airborne Equipment”.
3.1.2 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 use 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.
3.1.2.1 Compliant Architecture.
3.1.2.1.1 ADS-B equipment that meets the minimum performance requirements of TSO-C166b or TSO-C154c and is directly connected to a position source meeting the minimum performance requirements of any revision of the following TSOs may set the SDA = 2 without further analysis:
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 Satellite Based Augmentation System (SBAS);
TSO-C146, Stand-Alone Airborne Navigation Equipment Using the Global Positioning System (GPS) Augmented By the Satellite Based Augmentation System (SBAS); or TSO-C196, Airborne Supplemental Navigation Sensors for Global Positioning System Equipment using Aircraft-Based Augmentation.
3.1.2.1.2 For installations in aircraft with more complex system architectures, a system safety assessment, as described below, is required to set the SDA.
Installations of uncertified ADS-B systems must set SDA = 0 with the following exception: experimental category aircraft, including experimental light-sport aircraft (E-LSA) (Part 91 aircraft), may install unapproved equipment and set the SDA in accordance with the equipment manufacturer’s installation manual, provided the equipment has a statement of compliance to the performance requirements of § 91.227), from the equipment manufacturer(s).
3.1.2.2 Conducting the System Safety Assessment.
3.1.2.2.1 ADS-B systems using position sources not listed in section 3.1.2.1 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(), System Design and Analysis;
AC 23.1309-1(), System Safety Analysis and Assessment for Part 23 Airplanes;
SAE International (SAE) Aerospace Recommended Practice (ARP) 4761, Guidelines and Methods for Conducting the Safety Assessment Process on Civil Airborne Systems and Equipment; or SAE ARP 4754A, Guidelines for Development of Civil Aircraft and Systems.
3.1.2.2.2 If the system contains different design assurance levels for hardware and software, the worst-case design assurance level should be used. For example, if the hardware assurance level is C, and the software assurance level is B, the SDA would indicate the system has been qualified commensurate with a Major failure condition. If the ADS-B system is integrated with a noncompliant GPS, (for example, a GPS not compliant with §3.1.2.1), the SDA must be set to “0”.
Note: Although the direct effects to your aircraft of an ADS-B failure may be minor, the ADS-B OUT information will be used by other ADS-B IN 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 OUT system.
3.1.2.3 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, flightcrew controls, heading instruments, or antennas. In contrast, the position source installation must be compliant with the guidance in this AC, including design assurance considerations.
3.1.3 Position Latency.
Latency is the difference between the time when a measurement is taken to determine the aircraft’s geometric position and the time when the aircraft’s ADS-B equipment transmits that position measurement. Limiting the latency in ADS-B systems
10 minimizes the errors in the reported position. TSO-C166b and TSO-C154c ADS-B equipment compensate for latency by extrapolating the position based on velocity information. All applicants must demonstrate compliance with the latency requirements in section 3.1.3.1. This can be done by equipping with a compliant architecture such as the one listed in section 3.1.3.2 or performing an analysis such as the one detailed in section 3.1.3.3. Latency terms are further defined in 4.5.6Appendix C of this AC.
Note 1: To demonstrate compliance with § 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 RTCA, Inc. (RTCA) document (DO)-260B, Minimum Operational Performance Standards for 1090 MHz Extended Squitter Automatic Dependent Surveillance – Broadcast (ADS-B) and Traffic Information Services – Broadcast (TIS-B), with corrigendum 1, and RTCA/DO-282B, Minimum Operational Performance Standards for Universal Access Transceiver (UAT) Automatic Dependent Surveillance – Broadcast, with corrigendum 1.
3.1.3.1 Position Latency Requirements.
There are two position latency requirements associated with ADS-B OUT:
1. 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. To meet § 91.227, the total latency must be less than or equal to 2.0 seconds.
2. 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. To meet § 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 (that is, lead the aircraft position) by more than 0.2 seconds.
Note: RTCA Special Committee 186, which developed the ADS-B OUT minimum operational performance standards, 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 § 91.227 latency requirements support ATC separation services and the initial basic ADS-B IN applications.
However, we encourage you to minimize uncompensated latency as much as possible in your installation. Recommendations for minimizing latency are included in 4.5.6Appendix C of this AC.
3.1.3.2 Compliant Architecture.
ADS-B systems that 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 satisfy the total latency and uncompensated latency requirements. Systems with a
11 compliant architecture do not need to accomplish a position and velocity latency analysis.
3.1.3.3 Position Latency Analysis.
If you are installing an ADS-B system that does not have a compliant architecture described in section 3.1.3.2, 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. 4.5.6Appendix C of this AC provides for an acceptable method to complete the latency analysis.
3.1.4 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. § 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.
3.1.4.1 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-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: ARINC Characteristic 743A-5, GNSS Sensor, 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.
3.1.4.2 Integrity Metric Latency Analysis.
If you are installing an ADS-B system without a compliant architecture, like the one 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
12 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.
3.1.5 System Design Assurance (SDA) and Source Integrity Level (SIL) Latency.
§ 91.227 requires broadcasting changes in the SDA or SIL within 10 seconds. Changes in the SDA or SIL will typically occur when all position sources are lost, or 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 noncompliant GPS, the SDA and SIL must be set to “0”.
3.1.6 Populating Message Elements.
§ 91.227 lists parameters that must be populated (that is, not a null value) for operation in airspace defined by § 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.
3.2.1 Equipment Eligibility.
ADS-B equipment must meet the performance requirements specified in TSO-C166b or TSO-C154c. A compliant installation must meet the requirements in § 91.227. To deviate from any rule requirements, you must obtain a deviation approval from the FAA, in accordance with § 91.225(c) and § 91.227(f). Under those provisions, as specified in 14 CFR 21.618, this requires showing that factors or design features provide an equivalent level of safety that compensates for the standards from which a deviation is requested.
3.2.2 Installation Guidance.
3.2.2.1 UAT Systems With Mode S Transponders.
Do not install a UAT ADS-B OUT system with the capability to transmit a random 24-bit address in an aircraft that 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.
3.2.2.2 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
13 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.
3.2.2.3 Stand-Alone 1090ES Transmitters.
RTCA/DO-260B, section 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 § 91.227.
3.2.2.4 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 the anonymity (random address) feature. If dual ADS-B OUT systems of the same link are installed (for example, to increase dispatch reliability), the installation must preclude operation of both systems simultaneously. Also, dual systems must be the same version level;
that is, if the 1090ES system meets the requirements of RTCA/DO-260B (version 2), the UAT system must meet the requirements of RTCA/DO-282B (version 2).
Note: Installation of dual 1090ES and UAT ADS-B IN capability is acceptable and encouraged. Refer to AC 20-172() for ADS-B IN installation guidance.
3.2.3 Configuration of Associated Parameters.
This section provides additional guidance on setting key ADS-B OUT parameters.
Definitions for each of the following associated parameters are included in
4.5.6Appendix A of the AC.
3.2.3.1 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 currently 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 section 3.7.2.3 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.
14 Note 3: Installation instructions may require inputting the 24-bit address as an Octal, Decimal, or Hexadecimal number (that is, 50604331Octal = 10684633Decimal = A308D9Hex). Ensure you use the correct base number when configuring the ADS-B system.
3.2.3.2 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 § 91.227. The length and width code chosen should be the smallest value that encompasses the entire aircraft and any fixed objects.
For fixed-wing aircraft, this may be the nose, or other fixed object forward of the nose, such as a pitot probe. For rotorcraft, this may be the most forward, aft and lateral point the rotor blades sweep or some other fixed object such as a refueling boom. See (refer to figure 2 below).
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 Position of GNSS antenna ADS-B reference point Center of defining rectangle (center of solid box) ● Center of leading edge of Length Width code “box” Aerial refueling boom, or other fixed object extending beyond nose of vehicle
3.2.3.3 ADS-B IN Capability.
This parameter must be configured to indicate if the aircraft has an ADS-B IN system installed, and can process ADS-B messages to support at least one ADS-B IN application. For ease of installation, the parameter does not have to indicate the operational status of the ADS-B IN system. If the
15 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.
3.2.3.4 Emitter Category.
Set emitter category per manufacturer instructions. Table 1 below provides guidance on setting the emitter category that is appropriate for the type of aircraft it is being install on.
16 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 lbs 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 lbs 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 lbs 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 ≥ 300,000 lbs Any airplane with a maximum takeoff weight equal to or above 300,000 pounds.
High Performance > 5 G and > 400 TAS Any airplane, regardless of weight, that 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.
Parachute / Sky Diver For use by parachute / sky divers.
Ultralight Vehicle A vehicle that meets the requirements of 14 CFR
103.1.Light sport aircraft should not use the ultralight emitter category unless they meet 14 CFR 103.1.
UAV Any unmanned aerial vehicle or system regardless of weight.
Space/Trans-atmospheric Vehicle For use by space/trans-atmospheric vehicles.
No ADS-B Emitter Category Information Do not use this emitter category. Refer to category 0 above.
Surface Vehicle— Emergency Vehicle For use by surface emergency vehicles.
Surface Vehicle— Service Vehicle For use by surface vehicles.
Point Obstacle (Includes Tethered Balloons) For use by point obstacles to include tethered Balloons.
Cluster Obstacle For use by cluster obstacles.
Line Obstacle For use by line obstacles.
3.3 Position Source.
3.3.1 Equipment Eligibility.
§ 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 performance requirements in 4.5.6Appendix B of this AC. Compliance with the 4.5.6Appendix B requirements may be documented in the position source manufacturer’s installation instructions.
Note: Not all GNSS position sources will provide the same availability. Refer to
4.5.6Appendix B for more information on GNSS availability. The FAA recommends TSO-C145 or TSO-C146 position sources that meet the 4.5.6Appendix B requirements to maximize availability and ensure access to the airspace identified in § 91.225 after January 1, 2020.
3.3.2 Installation Guidance.
3.3.2.1 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 20-138(), Airworthiness Approval of Positioning and Navigation Systems.
3.3.2.2 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 that demonstrates 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.
3.3.2.3 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 4.5.6Appendix B of this AC.
18 Note: If a position source is unable to provide § 91.227 accuracy and integrity values, it will not qualify the aircraft to operate in airspace defined by § 91.225 after January 1, 2020.
3.3.2.4 Position Source Selection.
If multiple position sources (such as MMR/GPS, IRS/INS/ADIRU or GPS1 & GPS2) 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 flightcrew 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, accuracy metrics, and integrity metrics.
3.3.2.5 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 system without providing any navigation information to other onboard systems. As addressed in 4.5.6Appendix B of this AC, an integrated GNSS position source should still meet the requirements of TSO-C145(), TSO-C146(), or TSO-C196().
3.3.2.6 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 allow the time mark pulse to be asynchronous to the UTC second, 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.
3.3.3 Configuration of Associated Parameters.
This section provides additional guidance on setting key ADS-B OUT parameters.
Definitions for each of the following associated parameters are included in
4.5.6Appendix A.
3.3.3.1 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.
3.3.3.2 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 and an 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. Refer to section 3.5.3 of this AC for additional information on interfacing heading.
3.3.3.3 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 that derive SIL from GNSS position sources that are compliant with any revision of TSO-C129, TSO-C145, TSO-C146, or TSO-C196 and 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 noncompliant GPS, SIL must be set to “0”.
3.3.3.4 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.
3.3.3.5 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, although HPL values significantly smaller than 0.1 nautical mile (nm) can be output from single-frequency GNSS sources, the HPL 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