Appendix 1 A1-3 ICAO 24-bit address is required to be transmitted by 14 CFR 91.227 except when using the TSO-C154c anonymity feature.
o. IFR capability. This parameter existed in TSO-C166a and TSO-C154b compliant equipment, however it was removed from TSO-C166b and TSO-C154c equipment.
p. IDENT. A flag manually set by the pilot at the request of ATC, in ATCRBS, Mode S and ADS-B messages. The pilot manually enables the IDENT state, which highlights their aircraft on the controllers screen. IDENT is required to be transmitted by 14 CFR 91.227.
q. Latitude and longitude. These parameters are derived from the position source and provide a geometric based position. Reference all geometric position elements broadcast from the ADS-B unit to the World Geodetic System 1984 (WGS-84) ellipsoid. Latitude and longitude are required to be transmitted by 14 CFR 91.227.
r. Length and width of aircraft. This parameter provides ATC and other aircraft with quick reference to the aircraft’s dimensions while on the surface. Aircraft length and width is required to be transmitted by 14 CFR 91.227.
s. Mode 3/A code. Currently ATC automation relies on the Mode 3/A code to identify aircraft under radar surveillance and correlate the target to a flight plan. The mode 3/A code is a four digit number ranging from 0000 - 7777. Secondary Surveillance Radars (SSR) and ADS-B will concurrently provide surveillance, so the Mode 3/A code is included in the ADS-B OUT message and is required to be transmitted by 14 CFR 91.227.
t. Navigation Accuracy Category for Position (NACP). The NACP specifies the accuracy of the aircraft’s horizontal position information (latitude and longitude) transmitted from the aircraft’s avionics. The ADS-B equipment derives a NACP value from the position source’s accuracy output, such as the HFOM from the GNSS. The NACP specifies with 95% probability that the reported information is correct within an associated allowance. A minimum NACP value of eight must be transmitted to operate in airspace defined in 14 CFR 91.225. Table 9 provides the applicable NACP values.
Appendix 1 A1-4
Table 9. NACP Values
u. Navigation Accuracy Category for Velocity (NACV). The NACV is an estimate of the accuracy of the horizontal geometric velocity output. The coding of ZERO, indicating that the accuracy is unknown or either equal to or worse than 10 meters per second (m/s), is of little value to ADS-B applications. There is no vertical rate accuracy metric. A NACV of greater than or equal to 1 is required by 14 CFR 91.227.
v. Navigation Integrity Category (NIC). The NIC parameter specifies a position integrity containment radius. NIC is reported so that surveillance applications, such as ATC or other aircraft, may determine whether the reported geometric position has an acceptable level of integrity for the intended use. The NIC parameter is closely associated with the SIL. While NIC specifies the integrity containment radius, SIL specifies the probability of the actual position lying outside that containment radius without indication. ADS-B systems should derive the NIC from an approved position source’s integrity output, such as the horizontal protection level (HPL) from the GNSS. A minimum NIC value of seven must be transmitted to operate in airspace defined in 14 CFR 91.225. Table 10 provides the applicable NIC values.
NACP Horizontal Accuracy Bound 0 EPU ≥ 18.52 km (10nm) 1 EPU < 18.52 km (10nm) 2 EPU < 7.408 km (4nm) 3 EPU < 3.704 km (2nm) 4 EPU < 1852 m (1nm) 5 EPU < 926 m (0.5nm) 6 EPU < 555.6 m (0.3nm) 7 EPU < 185.2 m (0.1nm) 8 EPU < 92.6 m (0.05nm) 9 EPU < 30 m 10 EPU < 10 m 11 EPU < 3 m
Appendix 1 A1-5
Table 10. NIC Values
NIC Containment Radius 0 Unknown 1 R C < 37.04 km (20nm) 2 R C < 14.816 km ( 8nm) 3 R C < 7.408 km (4nm) 4 R C < 3.704 km (2nm) 5 R C < 1852 m (1nm) RC < 1111.2 m (0.6nm) RC < 926 m (0.5nm) 6 RC < 555.6 m (0.3nm) 7 R C < 370.4 m (0.2nm) 8 R C < 185.2 m (0.1nm) 9 R C < 75 m 10 R C < 25 m 11 R C < 7.5 m
w. NICBARO. NICBARO indicates if pressure altitude is provided by a single Gillham encoder or another more robust altitude source. Because of the potential for an undetected error in a Gillham encoding, many Gillham installations are cross-checked against a second altitude source.
NICBARO annotates the status of this cross-check.
x. Position. These parameters are derived from the position source and provide a geometric based position. Reference all geometric position elements broadcast from the ADS-B unit to the World Geodetic System 1984 (WGS-84) ellipsoid. Latitude and longitude is required to be transmitted by 14 CFR 91.227.
y. Receiving ATC services. A bit set in the ADS-B system of an aircraft indicating that the Mode A code is not set to 1200. This parameter existed in TSO-C166a and TSO-C154b compliant equipment, however it was removed from TSO-C166b and TSO-C154c equipment.
z. Single antenna bit. Indicates if the ADS-B equipment is transmitting through a single antenna.
aa. Source Integrity Level (SIL). The SIL field defines the probability of the reported horizontal position exceeding the radius of containment defined by the NIC, without alerting, assuming no avionics faults. Although the SIL assumes there are no un-annunciated faults in the avionics system, the SIL must consider the effects of a faulted Signal-In-Space (SIS), if a signal-inspace is used by the position source. A minimum SIL value of three must be transmitted to operate in airspace defined in 14 CFR 91.225. Table 11 outlines the SIL values.
Note: 1: The probability of an avionics fault causing the reported horizontal position to exceed the radius of containment defined by the NIC, without alerting,
Appendix 1 A1-6 is covered by the SDA parameter.
Note: 2: The SIL probability can be defined as either per sample or per hour as defined in the SIL supplement (SILSUPP).
Table 11. SIL Values, Probability of Exceeding the NIC Containment Radius.
SIL Value Probability of exceeding the NIC containment radius 3 ≤ 1x10-7 Per Hour or Sample 2 ≤ 1x10-5 Per Hour or Sample 1 ≤ 1x10-3 Per Hour or Sample 0 > 1x10 -3 Per Hour or Sample or Unknown
bb. Source Integrity Level Supplement (SILSUPP). The “SILSUPP” defines whether the reported SIL probability is based on a per hour probability or a per sample probability as defined in table 12.
Table 12. Source Integrity Level Supplement
SIL Supplement Basis for SIL Probability 1 Probability of exceedin g NIC containment radius is based on per sample 0 Probability of exceeding NIC contai nment radius is based on per hour
cc. System Design Assurance (SDA). The SDA parameter defines the failure condition that the ADS-B system is designed to support as defined in table 13. The supported failure condition will indicate the probability of an ADS-B system malfunction causing false or misleading position information or position quality metrics to be transmitted. This should include the probability of exceeding the containment radius without annunciation. Since the installer of ADS-B OUT equipment does not know how the broadcast data will be used, the installer cannot complete a Functional Hazard Assessment (FHA) evaluating the use of the broadcast data. The SDA provides a surrogate for such a FHA, by identifying the potential impact of an erroneous position report caused by an equipment malfunction. The definitions and probabilities associated with the supported failure effect are defined in AC 25.1309-1, System Design and Analysis, AC 23.1309-1(), System Safety Analysis and Assessment for Part 23 Airplanes, and AC 29-2, Certification of Transport Category Rotorcraft (Changes 1-3 incorporated). The SDA includes the position source, ADS-B equipment, and any intermediary devices that process the position data. 14 CFR 91.227 requires a SDA of 2 or 3 as defined in table 13.
Appendix 1 A1-7
Table 13. System Design Assurance
SDA Value Supported Failure Condition Note 2 Probability of Failure causing transmission of False or Misleading Information Note 3,4 Software & Hardware Design Assurance Level Note 1,3 3 Hazardous ≤ 1x10-7 Per Hour B 2 Major ≤ 1x10-5 Per Hour C 1 Minor ≤ 1x10-3 Per Hour D 0 Unknown/ No safety effect > 1x10-3 Per Hour or Unknown N/A
Note: 1: Software design assurance per RTCA/DO-178B, Software Considerations in Airborne Systems and Equipment Certification, or equivalent.
Airborne electronic hardware design assurance per RTCA/DO-254, Design Assurance Guidance for Airborne Electronic Hardware, or equivalent.
Note: 2: Supported failure classification defined in AC 25.1309-1, AC 23.1309-1, and AC 29-2.
Note: 3: Because the broadcast position can be used by any other ADS-B equipped aircraft or by ATC, 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 for the ADS-B system.
Note: 4: Includes probability of transmitting false or misleading latitude, longitude, or associated position accuracy and integrity metrics.
dd. TCAS installed and operational. This parameter indicates whether the aircraft is fitted with a TCAS II and if the TCAS II is turned on and operating in a mode that can generate resolution advisory alerts. The TCAS installed and operational parameter is required to be transmitted by 14 CFR 91.227.
ee. TCAS traffic status. This parameter indicates if a TCAS II equipped aircraft is currently generating a TCAS resolution advisory. The TCAS traffic status parameter is required to be transmitted by 14 CFR 91.227 if the aircraft is TCAS II equipped.
ff. Trajectory change report capability. This information is permanently set to zero in TSO-C166b or TSO-C154c equipment. No installation interface is required. Trajectory change reports are reserved for future use.
gg. Vertical rate. The barometric or geometric rate at which the aircraft is climbing or descending, measured in feet per minute. The vertical rate is typically generated by an air data computer or GNSS position source, or equipment which blends barometric vertical rate with inertial vertical rate and/or GNSS vertical rate.
Appendix 1 A1-8 hh. Version number. The applicable TSO Minimum Operational Performance Standard (MOPS) level is communicated through the version number, which is fixed at the time the ADS-B equipment is manufactured. Version two applies to ADS-B equipment that meets MOPS documents RTCA/DO-260B with Corrigendum 1 or RTCA/DO-282B with corrigendum 1.
ADS-B equipment outputting version two or higher is required by 14 CFR 91.227.
Appendix 2 A2-1 Appendix 2. Identifying and Qualifying ADS-B Position Sources
1. Purpose. This appendix defines the minimum requirements for position sources interfaced to ADS-B systems. The appendix also defines appropriate position source qualification methods when the existing GNSS TSOs do not contain specific requirements or test procedures. The position source manufacturer should provide design data where appropriate, preferably in the GNSS equipment installation manual, so that the installer can properly interface the position source to the ADS-B system. Position source suppliers must ensure that any supplied data is incorporated into the article design, and changes to any documented characteristics result in a change to the part number.
2. Organization. This appendix includes general guidance that applies to all position sources, as well as GNSS specific guidance. The appendix also provides high level requirements for tightly coupled GNSS/IRU position sources and non-GNSS position sources. All references in this AC to TSO-C129, TSO-C145, TSO-C146, and TSO-C196 refer to any revision of the TSO.
3. General Guidance for all Position Sources. All ADS-B position sources should provide the following outputs.
a. Position. The position source must provide a latitude and longitude output.
Requirements and test procedures in TSO-C129/145/146/196 are sufficient and GNSS equipment with Technical Standard Order Authorization (TSOA) for the aforementioned TSOs require no additional qualification for the position output.
b. Horizontal velocity. The position source must output north/south and east/west velocities. We recommend the position source also output the velocity in a ground speed and track angle format.
c. Position accuracy (horizontal). The position source must have a horizontal position accuracy output, and the output must have been qualified during the system’s TSO authorization or design approval. This output must describe the radius of a circle in the horizontal plane, with its center being at the true position which describes the region assured to contain the indicated horizontal position with at least 95% probability under fault-free conditions.
d. Position accuracy (vertical). The position source should output a vertical position accuracy metric. The vertical position accuracy metric must have been qualified during the system’s TSO authorization or design approval. This output must describe the vertical position accuracy with 95% probability under fault-free conditions.
e. Position integrity (horizontal). The position source must have a horizontal position integrity output qualified during the system’s TSO authorization or design approval. This integrity output should describe the radius of a circle in the horizontal plane, with its center being at the true position which describes the region assured to contain the indicated horizontal position with at least 99.99999% probability under fault-free avionics conditions. Position sources which degrade from a 99.99999% probability to a 99.999% probability (e.g., a tightlycoupled inertial/GNSS system after the loss of GNSS) can still be installed, however they won’t meet 14 CFR 91.227 following the degradation. In this case, the position source must have a
Appendix 2 A2-2 way of indicating the change to the ADS-B equipment. Additionally, if the change of probability is due to a change in position source, the new position source must meet all of the requirements in this appendix.
(1) Mode. If interpretation of the integrity output of the position source can change due to a change in the position source mode, the position source must have a way of communicating that change of mode to the ADS-B equipment. Additionally, the position source manufacturer should provide a description of the modes and a description of how the position source outputs the mode indication.
(2) Validity limit. If the integrity value of the output cannot be trusted beyond a certain limit, indicate this limitation in the design documentation.
(3) Integrity fault. The position source must be able to identify, and output, an indication of an integrity fault. This indication should occur within 8 seconds of output of an erroneous position. The position source manufacturer must provide information on how this integrity fault is output.
f. Position integrity (probability). The position source manufacturer must provide information describing the basis for the probability of exceeding the horizontal integrity containment radius. This basis must indicate the probability of exceeding the integrity containment radius as well as the sampling duration (per hour or per sample).
g. Signal-in-space error detection. The position source should provide a means to detect a SIS error when the system uses a SIS. The probability of missed detection for a faulty SIS should be less than 1x10-3. GNSS equipment provides the appropriate SIS error detection.
h. Velocity accuracy. The position source should have a velocity accuracy output that was qualified in conjunction with the system’s TSO authorization or design approval. In lieu of a dynamic output, the position source manufacturer may demonstrate a worst case velocity accuracy that can be assumed based on testing. A test for GNSS position sources is contained in the latest revision of AC 20-138C, Appendix 4. The position source manufacturer may propose a test method for non GNSS sources or an alternate test for GNSS sources during the TSO authorization or design approval.
i. Design assurance. The position source must support a major or greater failure effect.
This includes software compliant with RTCA/DO-178B, Software Considerations in Airborne Systems and Equipment Certification, Level C, and airborne electronic hardware (AEH) compliant with RTCA/DO-254, Level C. For airborne electronic hardware determined to be simple, RTCA/DO-254, paragraph 1.6 applies. Because the broadcast position can be used by any other ADS-B equipped aircraft or by ATC, 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 for the ADS-B system. The overall probability of a position source malfunction causing a position to be output which exceeds the output integrity radius must be less than 1x10-5 per hour.
Appendix 2 A2-3
j. Geometric altitude. The position source must have a geometric altitude output. The geometric altitude must be referenced to the WGS-84 ellipsoid.
k. Update rate. The position source must output a new position at least once per second.
Faster position update rates reduce latency of the transmitted position and are encouraged.
l. Position source latency. The position source manufacturer must provide position source latency information. Specifically, the manufacturer must provide the amount of position source total latency and uncompensated latency. Because the latency requirements are based on the entire ADS-B system, and not just the position source, the following position source latency targets are only guidelines. Position source uncompensated latency should be less than 200ms, compensated latency should be less than 500ms, and total latency should be less than 700ms.
Note: 1: System latency requirements are described in paragraph 3-1 of this AC.
Note: 2: This paragraph addresses position latency only.
m. Position, velocity, and accuracy time of applicability. For each position output by the source, a velocity, horizontal position accuracy metric and horizontal velocity accuracy metric must also be output. All measurements and metrics must have the same time of applicability. A horizontal position integrity metric must also be output, but its time of applicability may lag the position. See TSO-C145, TSO-C146, or TSO-C196 for additional information on the integrity time-to-alert.
n. Time mark. position sources should output a time mark identifying the Coordinated Universal Time (UTC) time of applicability of the position. The time mark can be used by the ADS-B equipment to reduce uncompensated latency.
o. Availability. 14 CFR 91.225 and 91.227 do not define an availability requirement, however it is a significant operational factor when selecting the position source, (see table 14, Estimated GNSS availabilities minimum threshold constellation).
4. GNSS position sources. Compliance to the applicable TSOs for GNSS position sources does not guarantee that the unit is suitable as an ADS-B position source. The information in this section describes an acceptable means to demonstrate compliance with ADS-B requirements not addressed by GNSS TSOs when using GNSS position sources for ADS-B.
a. Position. GNSS position sources must provide a latitude and longitude output.
Requirements and test procedures in TSO-C129/145/146/196 are sufficient and GNSS equipment with Technical Standard Order Authorization (TSOA) for the aforementioned TSOs require no additional qualification for the position output.
Note: The intent is to output position, velocity, and HFOM in a consistent manner for time of applicability (refer to DO-229D Section 2.1.2.6 and 2.1.2.6.2).
Appendix 2 A2-4
(1) TSO C129. The requirements outlined for 2D accuracy in paragraph (a)(3)(xvi) of TSO-C129 does not ensure full compliance for the GNSS unit. Additional means of compliance for this TSO requires GNSS manufacturers to substantiate that the latitude/longitude is output and referenced to WGS-84 coordinate system.
(2) TSO C129a. The requirements outlined for 2D accuracy in paragraph (a)(3)(xvi) of TSO-C129a does not ensure full compliance for the GNSS unit. Additional means of compliance for this TSO requires GNSS manufacturers to substantiate that the latitude/longitude is output and referenced to WGS-84 coordinate system.
(3) TSO C145/146 Rev a Class 1. Means of compliance for this TSO are defined in DO-229C, Minimum Operational Performance Standards for Global Positioning System/Wide Area Augmentation System Airborne Equipment, section 2.1.2.6.
(4) TSO C145/146 Rev a Class 2/3. Means of compliance for this TSO are defined in DO-229C sections 2.1.4.8 & 2.1.5.8.
(5) TSO C145/146 Rev b/c Class 1. Means of compliance for this TSO are defined in DO-229 D 2.1.2.6.
(6) TSO C145/146 Rev b/c Class 2/3. Means of compliance for this TSO are defined in DO-229D sections 2.1.4.8 & 2.1.5.8.
(7) TSO C196/196a. Means of compliance for this TSO are defined in DO-316, Minimum Operational Performance Standards (MOPS) for Global Positioning System/Aircraft Based Augmentation System Airborne Equipment, section 2.1.2.6.
b. Position source latency. GNSS position source manufacturer must provide position source latency information.
(1) TSO C129. Means of compliance for this TSO requires GNSS manufacturers to document the position source latency from Time Of Measurement (TOM) to time of position output.
If this latency exceeds 0.9 seconds, it may not support the two second ADS-B transmission latency at the aircraft level.
(2) TSO C129a. Means of compliance for this TSO requires GNSS manufacturers to document the position source latency from TOM to time of position output. If this latency exceeds
0.9 seconds, it may not support the two second ADS-B transmission latency at the aircraft level.
(3) TSO C145/146 Rev a Class 1. Means of compliance for this TSO are defined in DO-229C section 2.1.2.6.2.
(4) TSO C145/146 Rev a Class 2/3. Means of compliance for this TSO are defined in DO-229C sections 2.1.2.6.2 and 2.1.5.8.2.
Appendix 2 A2-5
(5) TSO C145/146 Rev b/c Class 1. Means of compliance for this TSO are defined in DO-229 D 2.1.2.6.2.
(6) TSO C145/146 Rev b/c Class 2/3. Means of compliance for this TSO are defined in DO-229D sections 2.1.2.6.2 and 2.1.5.8.2.
(7) TSO C196/196a. Means of compliance for this TSO are defined in DO-316 section
2.1.2.6.2.
c. Availability.
(1) Analysis has shown the following estimated availability for GPS receivers meeting the minimum TSO performance standards, (see table 14), assuming the minimum threshold GPS satellite constellation. The availability improves when the GPS constellation is full of operational satellites.
(2) The FAA plans to integrate back up surveillance systems with ADS-B, including SSR and Wide Area Multilateration, to mitigate the impact of loss of GNSS performance due to the health of the constellation. Backup surveillance will not be available in all airspace and operators should select an ADS-B positioning source that provides the necessary availability for their route of flight.
The FAA plans to implement a preflight availability determination system to assist operators in determining surveillance availability for ADS-B prior to flight. This tool will consider the GPS constellation that is predicted to be available at the planned flight time. The tool will also consider the status of existing backup surveillance capability and the required performance for the separation standard in use along the route of flight.
Table 14. Estimated GNSS Availabilities (Minimum Threshold Constellation)
Positioning Service (receiver standard) Predicted Availability (ADS-B Compliance) GPS (TSO-C129) (SA On) ≥ 89.0% GPS (TSO-C196) (SA Off) ≥ 99.0% GPS/SBAS (TSO-C145/TSO-C146) ≥ 99.9%
d. Horizontal position integrity. GNSS position sources must have a horizontal position integrity (e.g., HIL or HPL) output qualified during the system’s TSO authorization or design approval to determine NIC.
(1) TSO C129. The requirements outlined for Class A, B, and C equipment provides horizontal integrity through RAIM algorithms under DO-208, Minimum Operational Performance Standards for Airborne Supplemental Navigation Equipment Using Global Positioning System (GPS), change 1 section 2.2.1.13. But there is no requirement to compute or output HPL. To properly comply with the ADS-B requirements, additional means of compliance for this TSO requires GNSS manufacturers to provide substantiation data showing that the equipment outputs a 1x10-7/hr HPL based on the RAIM algorithm at least once per second that meets a 10 second time to alert. This AC recommends an 8 second time to alert. The protection level value is
Appendix 2 A2-6 acceptable as an HPL if the equipment performs the test in DO-208 change 1 section 2.5.2.5 using this protection level value for comparison against the alarm limit. Equipment using the least-squares residual RAIM method recommended in DO-208 change 1 Appendix F provides an acceptable HPL.
(2) TSO C129a. The requirements outlined for Class A, B, and C equipment provides horizontal integrity through RAIM algorithms under DO-208 change 1 section 2.2.1.13. But there is no requirement to compute or output HPL. To properly comply with the ADS-B requirements, additional means of compliance for this TSO requires GNSS manufacturers to provide substantiation data showing that the equipment outputs a 1x10-7/hr HPL based on the RAIM algorithm at least once per second that meets a 10 second time to alert. This Advisory Circular recommends an 8 second time to alert. The protection level value is acceptable as an HPL if the equipment performs the test in DO-208 change 1 section 2.5.2.5 using this protection level value for comparison against the alarm limit. Equipment using the least-squares residual RAIM method recommended in DO-208 change 1 Appendix F provides an acceptable HPL.
(3) TSO C145/146 Rev a Class 1. Means of compliance for this TSO are defined in DO-229C sections 2.1.2.6, 2.1.2.2.2, and 2.1.3.2.2. A summary of the latter requirements can be found in DO-229C section 2.1.1.13.1.
(4) TSO C145/146 Rev a Class 2/3. Means of compliance for this TSO are defined in DO-229C sections 2.1.2.6, 2.1.2.2.2, 2.1.3.2.2, 2.1.4.2.2, and 2.1.5.2.2. A summary of the latter requirements can be found in DO-229C section 2.1.1.13.1.
(5) TSO C145/146 Rev b/c Class 1. Means of compliance for this TSO are defined in DO-229D sections 2.1.2.6, 2.1.2.2.2, and 2.1.3.2.2. Related requirements can be found in DO-229D sections 2.1.1.4 and 2.1.4.9.
(6) TSO C145/146 Rev b/c Class 2/3. Means of compliance for this TSO are defined in DO-229D sections 2.1.2.6, 2.1.2.2.2, 2.1.3.2.2, 2.1.4.2.2, and 2.1.5.2.2. Related requirements can be found in DO-229D sections 2.1.1.4 and 2.1.4.9.
(7) TSO C196/196a. Means of compliance for this TSO are defined in DO-316 section
2.1.2.6, 2.1.2.2.2, and 2.1.3.2.
e. Position integrity (probability). GNSS position source manufacturer must provide information describing the basis for the probability of exceeding the horizontal integrity containment radius.
(1) TSO C129. Means of compliance for TSO-C129 are defined in DO-208 change 1 section 2.2.1.13.1 referring to Table 2-1.
(2) TSO C129a. Means of compliance for TSO-C129a are defined in DO-208 change 1 section 2.2.1.13.1 referring to Table 2-1.
(3) TSO C145/146 Rev a Class 1. Means of compliance for this TSO are defined in DO-229C section 2.1.2.2.2.1 for SBAS-based integrity. This requirement references Appendix J,