27 Chapter 4. T est & Evaluation
4-1. Ground Test.
a. Systems interface testing. Verify that the installed ADS-B equipment meets its intended function and transmits the appropriate information from each of the interfaced systems (position source, barometric altitude source, heading source, TCAS II, pilot interface, etc).
Coordinate with local ATC before broadcasting over the air to prevent being a source of interference to ATC or ADS-B IN equipped aircraft in the area. For example, transmitting airborne position reports with simulated airborne altitudes while on the surface will produce false targets for the ATC surveillance systems or airborne ADS-B IN equipped aircraft.
b. System latency. Latency is addressed through analysis rather than testing. See paragraph 3-1.
c. Rule compliance. Ensure the ADS-B system meets the requirements of 14 CFR 91.227.
(1) Accuracy and Integrity Performance. Ensure the installed system meets its stated accuracy and integrity performance under expected operating conditions. We recommend that you accomplish a GNSS performance prediction for the applicable time of your test to ensure the ADS-B system meets the predicted performance. In absence of predicted GNSS performance, demonstrate that you meet all 14 CFR 91.227 (c)(1) requirements, listed in table 2.
Table 2. Accuracy and Integrity Requirements NIC ≥ 7 R c < 370.4 m (0.2 nm) NACP ≥ 8 EPU < 92.6 m (0.05 nm) NACV ≥ 1 < 10 m/s SIL ≥ 3 ≤ 1x10-7 per hour or sample SDA ≥ 2 ≤ 1x10-5 per hour
(2) Parameters. Ensure all 14 CFR 91.227(d) parameters are properly populated and transmitted.
(3) Position accuracy. Position the aircraft on a surveyed location and validate the position transmitted from the ADS-B system. Ensure that the position transmitted is within the allotted NACP accuracy limit. For example, if the aircraft reports a NACP = 8, the ADS-B position should be within
92.6 meters, 0.05 nm. If the aircraft reports a NACP = 10, the ADS-B position should be within 10 meters. Reference appendix 1 for a complete list of NACP values. If the transmitted position accuracy is smaller or equal to the resolution of the test equipment, it is acceptable to use plus or minus one Least Significant Bit as the pass/fail criteria.
(4) Barometric Altitude Accuracy. Validate that the barometric altitude transmitted from the ADS-B system is accurate to within 125 feet. If the aircraft has a transponder installed, you must also validate that the ADS-B barometric altitude matches the transponder barometric altitude.
d. Electromagnetic Interface (EMI)/Electro Magnetic Compatibility (EMC) testing.
Provide an EMI/EMC test plan that demonstrates compliance with 14 CFR 23.1431 (a) and (b), 14 CFR 25.1353 (a) and (b), 14 CFR 25.1431 (a) and (c), 14 CFR 27.1301, 14 CFR 27.1309, 14 CFR 29.1353 (a) and (b), 14 CFR 29.1431 (a) and (b) as appropriate. Accomplish EMI/EMC testing to ensure that the ADS-B equipment does not provide an interference source on other installed systems on the aircraft. Additionally, ensure that equipment already installed in the aircraft does not interfere with the ADS-B system. If the STC or TC only involves a software change to an existing approved Mode S transponder installation, and the software update will not affect the systems response to EMI, you do not need to accomplish EMI testing again.
e. Human machine interface. Evaluate the flight crew interface for the ADS-B OUT system including the human-system interface and system behavior. The ADS-B OUT system must be compatible with the overall flight deck design characteristics (such as access to controls, sunlight readability, night lighting, etc.) as well as the airplane environment, such as vibrations.
(1) Information display. Evaluate the ADS-B OUT system to ensure displayed information is easily and clearly discernible, and has enough luminance, size, and visual contrast for the pilot to see and interpret it. Ensure the pilots have a clear, unobstructed, and undistorted view of the displayed information. Ensure information elements are distinct and permit the pilots to determine the source of the information elements if necessary, when there are multiple sources of the same kind of information.
(2) Controls and labeling. Evaluate the controls for the pilot interface to ensure they are plainly marked as to their intended function, provide convenient operation, and prevent confusion and inadvertent operation of both the ADS-B system, and the other systems with which they interact.
Evaluate the acronyms, labels, and annunciations to ensure they are used consistently in the flight deck, and do not cause confusion or errors. If a control performs more than one function, evaluate the labels to ensure the labels include all intended functions, unless the function of the control is obvious.
During evaluation, consider line select keys, touch screens or cursor controlled devices (e.g., trackballs) as these can be susceptible to unintended mode selection resulting from their location in the flight deck (e.g., proximity to a foot rest or adjacent to a temporary stowage area).
(3) Annunciations and alerts. Evaluate all ADS-B annunciations and alerts to ensure they are clear and unambiguous, and provide attention-getting and saliency appropriate to the type of alert.
Compliance with AC 25-1322-1, AC 27.1322, and AC 29.1322 should be considered when evaluating ADS-B annunciations and alerts. The colors yellow/amber and red should be restricted to cautions and warnings, respectively. Evaluate the annunciations and indications to ensure they are operationally relevant and limited to minimize the adverse effects on flight crew workload. When an annunciation is provided for the status or mode of a system, it is recommended that the annunciation indicate the actual state of the system, and not just the position of a switch.
(4) Pilot interface errors. Installations not providing a single point of entry for the ADS-B and transponder for the Mode 3/A code, IDENT, and emergency status must accomplish an evaluation of the pilot interface controls to determine that they are designed to minimize entry errors by the flight
29 crew, and enable the flight crew to detect and correct errors that do occur. System interface design must also be evaluated to ensure that dual entry of the Mode 3/A code, IDENT, and emergency status does not introduce significant additional workload, particularly when communicating an aircraft emergency. Evaluations should consider pilot-detected and undetected error rates, pilot workload, as well as training times. See paragraph 3-7c(5) for additional information on transponder and ADS-B system single point of entry.
(5) Lighting. Evaluate all foreseeable conditions relative to lighting, including failure modes such as lighting and power system failure, and day and night operations.
f. Transponder regression testing. At a minimum, use the procedures outlined in AC 43-6(), Altitude Reporting Equipment and Transponder System Maintenance and Inspection Practices, to validate that the transponder is operating normally following the ADS-B installation. Use the procedures outlined in AC 20-151() for ADS-B systems that include installation of a new or modified Mode S transponder. If you are installing a new air-ground status capability for the ADS-B system and this functionality is also interfaced to the transponder, you must ensure that replies to the Mode A/C and ATCRBS / Mode S all-call interrogations are inhibited on the ground.
g. ICAO 24-bit address. For U.S. civil aircraft, demonstrate that the 24-bit address transmitted by the system correlates to the aircraft registration number. If the system has a separate Mode S transponder and UAT ADS-B system installed, then ensure both the transponder and ADS-B system both transmit the same correct ICAO 24-bit address. For non- U.S. registered aircraft, verify that the ICAO 24-bit address is the address assigned to the aircraft by the responsible State authority.
h. Self test. Evaluate the ADS-B self-test features (if provided) and failure mode annunciations to ensure that the pilot is able to determine whether the system is functioning properly.
i. Position source failure. Demonstrate that a failure or loss of the position source results in an indication to the operator of an ADS-B function failure. If a secondary position source is interfaced to the ADS-B equipment, ensure it meets all guidance in this AC. If the change from the primary position source to the secondary position source requires a change in SIL or SDA, ensure these changes are accomplished within 10 seconds.
j. Air-ground status. Verify that the air-ground inputs (or algorithms) are functioning properly and that the ADS-B system transmits the appropriate airborne messages or surface messages based on the air-ground status. This can be accomplished with simulated inputs to the appropriate sensors or accomplished in conjunction with the flight test. Rotorcraft may consider hover taxi as in the air
k. Transmit power. Transmit power testing must be accomplished if a new antenna has been installed, an existing antenna has been relocated, if a diplexer has been installed into an existing antenna system, or the output specifications on the transponder have changed. Perform the following testing to validate transmit power:
30 Note: Upgrading a previously installed and approved TSO-C112() Mode S transponder to include ADS-B functionality does not require transmit power testing unless a new antenna has been installed, the antenna location has changed, or the output specifications on the transponder have changed.
(1) 1090ES transmitter. Verify that the peak pulse power at the antenna end of the transmission line meets the minimum and maximum power levels summarized in table 3, considering the test equipment antenna gain and path loss. Repeat the measurement in each quadrant of the antenna pattern (forward, aft, left, right).
Table 3. Minimum and Maximum Transmitted Power from TSO-C166b
Tested Transmitter Class Minimum Power Maximum Power A1 21.0 dBW 27.0 dBW A1S 21.0 dBW 27.0 dBW B1 21.0 dBW 27.0 dBW B1S 21.0 dBW 27.0 dBW A2 21.0 dBW 27.0 dBW A3 23.0 dBW 27.0 dBW
(2) UAT transmitter. Verify that the peak pulse power at the antenna end of the transmission line meets the minimum and maximum power levels summarized in table 4, considering the test equipment antenna gain and path loss. Repeat the measurement in each quadrant of the antenna pattern (forward, aft, left, right).
Table 4. Minimum and Maximum Transmitted Power from TSO-C154c
Tested Transmitter Class Minimum Power Maximum Power A1H 12.0 dBW 16.0 dBW A1S 12.0 dBW 16.0 dBW B1 12.0 dBW 16.0 dBW B1S 12.0 dBW 16.0 dBW A2 12.0 dBW 16.0 dBW A3 20.0 dBW 24.0 dBW
l. TCAS. If a TCAS II system is installed on the aircraft, ensure that the proper messages are transmitted by the ADS-B system when the TCAS II is on and operating in a mode that can provide RAs. No TCAS II system regression testing beyond the ground interface testing covered in this section is required.
m. Transponder all-call inhibit. When ADS-B functionality resides in a Mode S transponder, conduct a test which demonstrates that replies to Mode A/C/S all-call and Mode S-only all-call interrogations are inhibited on the ground. Also demonstrate that replies to discrete interrogations are not inhibited.
n. Mode 3/A code and emergency code. Demonstrate that the correct Mode 3/A code and IDENT is transmitted. Do not transmit the 7500, 7600, or 7700 emergency codes over the air during ground or flight testing. If testing emergency codes is desired, contact the local ATC facility and coordinate testing to prevent a nuisance emergency response.
4-2. Flight Test.
a. Mutual interference. During all phases of flight, demonstrate that there is no mutual interference with any other aircraft system. Have all installed systems operating during the flight test.
b. Other system performance. Demonstrate the proper performance of any previously installed aircraft system(s) that required changes as a result of the ADS-B installation in accordance with the applicable policy. This can be accomplished with standard regression test procedures for the other installed system, and does not require a unique test for ADS-B.
c. User interface. Exercise all user inputs. If separate user inputs are required for the transponder and ADS-B systems, evaluate the flight manual procedures for ensuring that the same Mode 3/A code, IDENT, and emergency codes are transmitted from both systems.
4-3. In-Flight Test with FAA Ground System. Perform a flight test to show that the installed system performs properly with the FAA ground system. The test will verify that the FAA ground system properly receives the aircraft’s ADS-B broadcast messages, there are no drop outs and the information transmitted is complete and correct. Currently the only method available to accomplish the flight test is to fly within ADS-B service coverage and accomplish a post flight analysis of the data received from the FAA. This test is intended to evaluate the design interface for the position source and the ADS-B equipment. If you have flight test data from a previous STC or TC which established this compatibility, you do not need to re-accomplish the flight test.
Note: 1: This flight test is intended to complete a design approval under an STC or TC application; it is not intended for the alteration of individual aircraft.
Note: 2: Follow your standard process for requesting flight test authorization, there are no unique flight test authorization requirements for ADS-B flight tests.
a. Preflight coordination.
(1) Data retrieval. At least 48 hours prior to the flight, notify the FAA by e-mailing 9-avs-air-130flttest@FAA.gov that you require data from the flight test to support post flight analysis. Include contact information for your ACO point of contact, aircraft registration number or applicable call sign, 24-bit address, expected date, location and approximate time of the flight.
(2) ATC coordination. There is no ADS-B specific requirement to coordinate the flight test in advance with ATC. Follow normal flight test procedures for coordinating with ATC.
b. Flight test profile. This profile is intended to be flown on all ADS-B system approvals.
The profile need not be flown exactly, and variances for ATC clearances and vectors are acceptable. The flight test should be at least 1 hour long. If the profile is completed in less than 1 hour, continue the flight until enough data is collected. The flight test may not be performed using the random UAT 24-bit address feature, since the 24-bit address is a key field in retrieving the ATC flight profile data. The profile discussed in paragraph 4-3b(3) thru (7) below may be flown in any order.
(1) Location of flight. The flight may be accomplished in any airspace that has FAA ADS-B ground station coverage. See the following web site for information on existing ADS-B coverage in the National Air Space (NAS):
http://www.faa.gov/about/office_org/headquarters_offices/ato/service_units/enroute/surveillance _broadcast/coverage/
(2) Distance from ground station. This flight profile does not specify the distance the aircraft must be from an ADS-B ground station. Transmit power is evaluated through ground testing instead of demonstrating a minimum air-to-ground reception distance.
(3) Altitude. Fly the aircraft at multiple altitudes throughout the flight within ADS-B coverage. There is no maximum or minimum altitude required for the flight test.
(4) Turns. Verify the ADS-B system performs properly during turning maneuvers.
During the flight, place the aircraft in various normal configurations such as takeoff, approach, landing, and cruise configuration if appropriate for the airframe. During the flight, perform at least two left and two right 360-degree turns. Table 5 provides suggested altitude, speed and bank angle at which these turns should be made. The intent of this test is to ensure the ADS-B system operates properly over the normal flight regimes of the aircraft under test. Variations on altitude, speed and bank angle are acceptable as long as the intent of the test is met.
Table 5. Turns
Part 23 Aircraft Configuration Altitude Range AGL Speed Range Bank Angle Takeoff 3000-5000 1.4 V S 30 0 Approach or Landing 2000-7000 1.4 V S 30 0 Cruise 7000-10000 1.5 V S to 1.8 VS 300 Part 25 Aircraft Configuration Altitude Range Speed Range Bank Angle Takeoff 3000-5000 V 2 + 20 kts 30 0 Approach or Landing 2000-7000 V APP + 20 kts 30 0 Cruise 7000-10000 1.5 V S to 1.8 VS 30 0 Part 27 Rotorcraft Configuration Altitude Range Speed Range Bank Angle Landing 1000-3000 V Y + 10 kts 30 0 Cruise 2000-5000 0.8 V NE or 0.8 VH 300 Part 29 Rotorcraft Configuration Altitude Range Speed Range Bank Angle Landing 1000-3000 V Y + 10 kts 30 0 Cruise 2000-10000 0.8 V NE or 0.8 VH 30 0
(5) Climbs/descents. Verify the ADS-B system performs properly during climbs and descents. Table 6 provides a suggested rate at which climbs should be made during the test flight. Table 7 provides a suggested rate at which descents should be made during the test flight.
Climbs and descents should be at least one minute in length. The intent of this test is to ensure the ADS-B system operates properly over the flight regime of the aircraft under test. Variations on climb and descent rates are acceptable as long as the intent of the test is met.
.
Table 6. Climb Speeds
Configuration Part 23 Aircraft Part 25 Aircraft Part 27 Rotorcraft Part 29 Rotorcraft Take off V Y V FE - 10 kts V Y VY Cruise V Y V MO - 10 kts 0.8 V NE or 0.8 VH 0.8 VNE or 0.8 VH
Table 7. Decent Speeds
Configuration Part 23 Aircraft Part 25 Aircraft Part 27 Rotorcraft Part 29 Rotorcraft Cruise V NE-10 V MO - 10 kts 0.8 V NE or 0.8 VH 0.8 VNE or 0.8 VH Approach V FE-10 V FE - 10 kts V Y + 10 kts VY + 10 kts Landing V FE-10 V FE - 10 kts N/A N/A
(6) Position accuracy. Utilizing a known waypoint, fly a north/south course that crosses the defined waypoint followed by an east/west course that crosses the same defined way point.
c. Post-flight data retrieval. Within 48 hours of completing the STC or TC flight test against the FAA ground stations, email: amc-ajw-sbsm@faa.gov, to request flight data from your flight. You must include your Type Inspection Authorization, name and email address of your ACO project engineer, aircraft registration number or applicable call sign, 24-bit address, date, location and time of the flight.
d. Post-flight data analysis. You must accomplish a post flight data analysis to ensure that the aircraft is transmitting accurate ADS-B information. Ensure all data associated with the track is consistent, such as position, 24-bit address, velocity, flight ID, barometric altitude, Mode 3/A code, emitter category, and geometric altitude. The post flight data analysis should also reveal if there were any unexpected data dropouts that might be caused from intermittent wiring interfaces or interface incompatibility. The flight test does not require the use of a truth source to accomplish post flight data analysis, however the FAA will provide radar data when available to help analyze the flight track.
At a minimum, analyze the following areas:
(1) Rule compliance. Review the data from the FAA ground system for the flight to ensure the installed system meets its stated accuracy and integrity performance under flight conditions.
We recommend that you accomplish a GNSS performance prediction for the applicable time of your test and ensure the ADS-B system meets the predicted performance. Due to the design of existing GNSS receivers and typical GPS constellation configurations, there will be time periods where unaugmented GNSS solutions drop below the NIC and NACp performance required by the rule.
Such outages usually do not occur for more than 20 minutes and many are of much shorter durations.
If the integrity and accuracy of an existing GNSS installation does not meet the rule requirements during the test flight, the applicant should show that poor performance was caused by the constellation during the period of time that the flight occurred. If that cannot be established as the cause of the poor performance, then there may be a problem with the position sensor installation that needs to be investigated and resolved. Resolution of this type of issue will probably require the involvement of the position source manufacturer. There may also be short periods where position messages transmit NIC=0, velocity messages transmit NACv=0, and status messages transmit NACp=0, SIL=0. These can be caused by antenna shadowing and switching effects, and do not indicate an installation problem if they are infrequent and of short duration. All such outages must be less than 5 seconds in duration to avoid operational impacts. This condition may not occur more often than once every 1000 position transmissions when averaging all outages over the flight duration. If this condition occurs more often during the flight test, then the applicant must establish root cause and provide a solution prior to granting installation approval. Demonstrate that you meet all 14 CFR 91.227 (c)(1) requirements, listed in table 8, accuracy and integrity requirements during flight.
Table 8. Accuracy and Integrity Requirements During Flight
Ensure NIC ≥ 7 throughout the flight. R c <370.4 m (0.2 nm) Ensure NACP ≥ 8 throughout the flight. EPU <92.6 m (0.05 nm) Ensure NACV ≥ 1 throughout the flight. < 10 m/s Ensure SIL ≥ 3 throughout the flight ≤1x10 7 Ensure SDA ≥ 2 throughout the flight ≤1x10-5 .
(2) Position accuracy/integrity. Compare the track received by the FAA ground system with the actual flight track. There is no specific tolerance for this test; rather the applicant must show there are no gross position errors, track offsets or discontinuities, or other obvious anomalies.
(3) Velocity accuracy. Compare the velocity received by the FAA ADS-B ground system with the actual velocities flown. There is no specific tolerance for this test; rather you must show that they compare reasonably, and that there are no gross velocity errors.
(4) Geometric altitude Accuracy. Compare the geometric altitude received by the FAA ground system with the geometric altitude flown. There is no specific tolerance for this test; rather you must show that they compare reasonably, and that there are no gross geometric altitude errors.
(5) Barometric pressure altitude accuracy. Compare the barometric pressure altitude received by the FAA ground system with the actual barometric pressure altitude flown. There is no specific tolerance for this test; rather you must show that they compare reasonably, and that there are no gross barometric pressure altitude errors.
(6) Validity checks. The FAA plans to utilize radar, multilateration, and UAT passive ranging as independent validity checks for ADS-B. The validity check will indicate “valid” when the independent check is able to validate the ADS-B position, “invalid” when it determines the ADS-B position is out of tolerance, and “unknown” if it is unable to accomplish the validity check. If a validity or an enhanced validity status is provided in the flight test data, then you must show that it never indicates invalid.
Note: Validity checks are planned to ensure the ADS-B position is within 0.56 nm in terminal airspace and 1.9 nm in en route airspace. Enhanced validity checks are planned to ensure the ADS-B position is within 0.2 nm within approximately 15 nm of terminal radars and close proximity to airports with Airport Surface Detection Equipment, Model X (ASDE-X) systems.
4-4. International Flight Test Options. If the aircraft is being flight tested outside of the United States, it is acceptable to perform the flight test against another Air Navigation Service Provider’s (ANSP) ground system. Other ANSP’s ground systems must be fully operational and appropriately qualified to provide ATC separation services. Other ANSP ground systems must also be able to provide all parameters required by 14 CFR 91.227. You will have to work with the foreign ANSP to retrieve the necessary data.
4-5. Subsequent Flight Test Data Reuse. The flight test guidelines in paragraph 4-3 apply to initial STC/TC applications. Flight test data from a similar installation, covered under a previous STC, may be used in-lieu-of a new flight test if the following conditions can be confirmed through the documentation of the previous STC:
a. The position source must be identical to that of the other STC documentation. Equipment families that use the same baseline design may make a case for equivalence.
b. The ADS-B equipment must be identical to that of the other STC/TC documentation.
Equipment families that use the same baseline design may make a case for equivalence.
c. A direct interface must be used between the position source and the ADS-B equipment, and that interface must be identical to that of the previous STC. Aircraft with data concentrators will have to re-accomplish the flight test, even if the equipment is identical.
d. The air-data interface to the ADS-B equipment must be identical to that of the previous STC. The actual air-data source may be different equipment, only the interface to the ADS-B equipment needs to be identical. However, if the air-data source is different more extensive ground testing should be accomplished, to include a dynamic test where the air-data source has simulated inputs from sea level to the maximum certified operating altitude of the aircraft. Care should be taken to ensure that broadcast of simulated altitude information does not cause interference with ATC or ADS-B IN applications.
e. The heading interface to the ADS-B equipment (if applicable) must be identical to that of the previous STC. The heading source may be different, only the interface to the ADS-B equipment needs to be identical. If the heading source is different, testing should be accomplished, to include positioning the aircraft at multiple headings on the surface to verify heading accuracy.
f. The TCAS interface to the ADS-B equipment must be identical to that of the previous STC.
The TCAS equipment may be different, only the interface to the ADS-B equipment needs to be identical.
Appendix 1 A1-1 Appendix 1. Message Elements Descriptions
1. Purpose. This appendix provides a description of the message elements that may be contained in an ADS-B message.
2. Message Elements.
a. ADS-B IN capability. Two messages indicate the ADS-B IN status of the aircraft. The 1090 ADS-B IN message indicates if the aircraft has the ability to receive 1090ES ADS-B messages installed. The UAT ADS-B IN message indicates if the aircraft has the ability to receive UAT ADS-B messages installed. An indication of ADS-B IN capability is important because TIS-B and ADS-R services are provided specific to an aircraft’s position relative to other aircraft. The FAA may only provide complete TIS-B and ADS-R services to aircraft that indicate they are ADS-B IN capable. ADS-B IN capability is required to be transmitted by 14 CFR
91.227.
b. Airspeed. Optionally, true airspeed or indicated airspeed may be transmitted. The airspeed source should be approved to output airspeed data. An air data computer meeting the minimum performance requirements of TSO-C106 is one acceptable source. Do not interface an airspeed source to the ADS-B that has not been approved for cockpit display.
c. Barometric pressure altitude. This parameter indicates the aircraft’s barometric pressure altitude referenced to standard sea level pressure of 29.92 inches of mercury or 1013.2 hectopascals. The barometric pressure altitude is required to be transmitted by 14 CFR 91.227.
d. Call Sign/flight ID. The term “aircraft call sign” is the radiotelephony call sign assigned to an aircraft for voice communications purposes. (This term is sometimes used interchangeably with “flight identification” or “flight ID”). For general aviation aircraft, the aircraft call sign is normally the national registration number; for airline and commuter aircraft, the call sign is usually comprised of the company identification and flight number (and therefore not linked to a particular airframe) and, for the military, it usually consists of numbers and code words with special significance for the operation conducted. The call sign or aircraft registration number is required to be transmitted by 14 CFR 91.227 except when using the TSO-C154c anonymity feature.
e. Emergency status. This parameter alerts ATC that the aircraft is experiencing emergency conditions and indicates the type of emergency. Applicable emergency codes are found in ICAO Annex 10 Volume 4, Surveillance Radar and Collision Avoidance Systems. This information alerts ATC to potential danger to the aircraft so it can take appropriate action.
Emergency status is required to be transmitted by 14 CFR 91.227.
f. Emitter Category. The emitter category provides an indication of the aircraft’s size and performance capabilities. Emitter categories are defined in TSO-C166b and TSO-C154c.
Emitter category is designed primarily to provide information on the wake turbulence that an aircraft produces. Emitter category is required to be transmitted by 14 CFR 91.227.
Appendix 1 A1-2
g. Geometric altitude. The geometric altitude is a measure of altitude provided by a satellite-based position service and is not affected by atmospheric pressure. Geometric altitude is only available with a GNSS position source. Geometric altitude for ADS-B purposes is the height above the WGS-84 ellipsoid (HAE). Geometric altitude is required to be transmitted by 14 CFR 91.227.
h. Geometric vertical accuracy (GVA). The GVA indicates the 95% accuracy of the reported vertical position (geometric altitude) within an associated allowance.
i. GNSS antenna offset and position offset applied.
(1) The GNSS antenna offset indicates the longitudinal distance between the nose of the aircraft and the GNSS antenna and the lateral distance between the longitudinal center line of the aircraft and the GNSS antenna.
(2) The position offset applied setting of the GNSS antenna offset indicates that the broadcast position is referenced to the aircraft’s ADS-B position reference point versus the GNSS antenna location. See RTCA/DO-242A, Min Aviation System Performance Standards for ADS-B, change 1, paragraph 2.1.2.5 and figure 2-1 for a depiction of the ADS-B position reference point.
j. Ground speed. This parameter is also derived from the position sensor and provides ATC with the aircraft’s speed over the ground. This parameter is reported in the surface position message.
k. Ground track angle. The ground track angle is the direction of the horizontal velocity vector over the ground. Ground track or heading is required to be transmitted while on the ground in order to transmit complete velocity information.
l. Heading. Heading indicates the direction in which the nose of the aircraft is pointing.
There is no heading accuracy metric. Heading or ground track is required to be transmitted while on the ground in order to transmit complete velocity information.
m. Horizontal velocity. The horizontal velocity provides the rate at which an aircraft changes its horizontal position with a clearly stated direction. Horizontal velocity is provided with the north/south velocity and the east/west velocity parameters while airborne. Horizontal velocity is provided by a combination of the ground speed and heading or ground track while on the surface.
TSO-C166b and TSO-C154c require that the north/south velocity, east/west velocity, ground speed, and ground track come from the same source as the position. Heading information may come from a separate source. Horizontal velocity is required to be transmitted by 14 CFR 91.227.
n. ICAO 24-bit address. A unique address assigned to an aircraft during the registration process. ICAO 24-bit addresses are defined blocks of addresses assigned for participating countries or states worldwide. In the United States, civil aircraft are assigned an address from an encoding scheme based on the aircraft registration number (“N” number). Additional information regarding the 24-bit address can be found in the ICAO Annex 10, Part I, Volume III, appendix to Chapter 9, A World-Wide Scheme for the Allocation, Assignment and Application of Aircraft Addresses. The