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
20 design data to determine if all error sources are taken into consideration, or if the position source limits the HPL output, when computing an unaugmented 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 unaugmented 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 that limits the NIC ≤ 8. Refer to section
4.5.6Appendix B, of this AC for additional information regarding HPL considerations.
3.3.3.6 Navigation Accuracy Category for Position (NACP).
The ADS-B equipment must set the NACP based on the real-time 95-percent accuracy metric provided by the position source. When interfacing GNSS sources, the NACP should be based on a qualified Horizontal Figure of Merit (HFOM).
3.3.3.7 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.
3.3.3.7.1 A NACV = 1 (< 10 m/s) may be permanently set at installation for GNSS equipment passing the tests identified in 4.5.6Appendix B of this AC, or may be set dynamically from velocity accuracy output of a position source qualified in accordance with the guidance in 4.5.6Appendix B.
3.3.3.7.2 A NACV = 2 (< 3 m/s) mustbe set dynamically from velocity accuracy output of a position source qualified in accordance with the
4.5.6Appendix B guidance. Do not permanently pre-set a NACV = 2 at installation, even if the position source has passed the tests identified in
4.5.6Appendix B.
3.3.3.7.3 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.
3.3.3.8 Geometric Altitude.
Ensure 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 the ADS-B equipment has demonstrated during design approval that it can properly convert HAG to HAE using the same model as the position
21 source. It would also be acceptable to demonstrate that the error due to conversion of HAG to HAE does not cause the GVA to be exceeded.
3.3.3.9 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 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”.
3.3.3.10 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 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.
3.4.1 Equipment Eligibility.
3.4.1.1 Use barometric altitude from a barometric altimeter that meets the minimum performance requirements of 14 CFR 91.217. The following three subparagraphs are each an acceptable means of compliance.
3.4.1.1.1 TSO-C10, Altimeter, Pressure Actuated, Sensitive Type (any revision)
3.4.1.1.2 TSO-C106, Air Data Computer (any revision)
3.4.1.1.3 Ensure the equipment was tested and calibrated to transmit altitude data corresponding within 125 feet (on a 95-percent probability basis) of the indicated or calibrated datum of the altimeter normally used to maintain flight altitude, with that altimeter referenced to 29.92 inches of mercury for altitudes from sea level to the maximum operating altitude of the aircraft.
3.4.1.2 If appropriate, use a digitizer meeting the minimum performance requirements of any revision of TSO-C88, Automatic Pressure Altitude Reporting Code-Generating Equipment.
3.4.2 Installation Guidance.
3.4.2.1 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.
3.4.2.2 § 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 part 91, appendix G (Operations in Reduced Vertical Separation Minimum (RVSM) Airspace) accuracy, that resolution and accuracy should be reflected in the ADS-B message.
3.4.2.3 If a secondary altitude source is used 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 the altitude source remains the same for both the transponder and ADS-B system.
3.4.3 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:
3.4.3.1 Barometric Altitude.
The ADS-B equipment must update the barometric altitude based on the real-time barometric altitude provided by the barometric altitude source.
3.4.3.2 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 that dynamically crosscheck 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.