Appendix 3
(3) The applicant must identify any conditions or constraints on path steering performance (for example, autopilot engaged, FD with map display, and/or CDI/map scaling criteria). This is particularly true for RNP values less than RNP 1.0.
(4) The RNP navigation system must provide an alert prior to the upcoming waypoint when the system cannot support the upcoming RNP value.
(5) The deviation guidance cues must be scaled to the RNP value.
c. The RNP navigation system must provide an alert for any failure mode that potentially affects the navigation performance relative to the selected RNP value. Failure modes may include loss of electrical power, loss of signal reception, and RNP equipment failure, including navigation performance degradation, resulting in a loss of RNP containment integrity. The applicant should verify that a visible alert occurs within the flight crew’s primary field of view when loss of navigation capability and/or loss of integrity are experienced.
A3-6. Fixed Radius Transitions.
FRTs are a waypoint transition between enroute legs using a defined radius. The intent is to define waypoint transitions along airways where separation between parallel routes is required and fly-by transitions are not compatible with the separation criteria. RTCA/DO-283B paragraph 2.2.1.2.9.2 defines equipment requirements for FRTs consistent with the aircraft performance requirements found in RTCA/DO-236C, Chg 1, paragraph 3.2.5.4.2.
A3-7. Time of Arrival Control.
TOAC is an advance RNP function that is not well defined for either equipment requirements or airspace implementation. RTCA/DO-283B paragraph 2.2.4 provides an initial implementation method for RNP equipment that is consistent with RTCA/DO-236C, Chg 1 paragraph 2.2. This section will be updated in the future consistent with TOAC airspace implementation plans.
A3-7
Appendix 4 Appendix 4. GNSS Tests to Support ADS-B.
A4-1. Introduction.
a. The information in this appendix describes bench test procedures that GNSS equipment manufacturers can use as an acceptable means to establish the GNSS equipment meets the required outputs described in AC 20-165 (latest revision). This appendix only addresses those ADS-B parameters that require specific tests because the GNSS TSOs do not adequately address the parameter. Other ADS-B parameters simply require coordination among the ADS-B and GNSS equipment manufacturers to properly integrate the equipment. A complete requirements compliance description will be contained in AC 20-165A (or later revision), appendix 2.
b. The tests are only required if the equipment manufacturer chooses to have their equipment provide inputs to ADS-B equipment. Which tests are necessary to qualify as an ADS-B position source is dependent upon which TSO the GNSS equipment has. The tests described below are intended for generating data to prove compliance with the following ADS B parameters if the GNSS TSO requirements are not adequate: velocity accuracy, height above ellipsoid (HAE), horizontal/vertical position accuracy metric, and true track angle/true track angle validity.
A4-2. Velocity Accuracy and Velocity Figure of Merit Tests.
a. All GNSS TSO equipment should use the tests in paragraphs A4-3 through A4-8 to demonstrate both velocity accuracy and velocity figure of merit qualifying as navigation accuracy category - velocity (NACV) = 1. Manufacturers that want their equipment qualified NACV = 2 must also complete the test in paragraph A4-9.
b. AC 20-165 (latest revision), appendix 2 (paragraphs 3h and 4n in revision ‘A’), state that installations with a position source capable of providing velocity accuracy should have the NACV derived from the position source, and the velocity accuracy should be validated during the position source manufacturer’s certification testing. The following procedures, developed by RTCA SC-159, are one means of accomplishing this testing.
c. The purpose of the GNSS velocity accuracy test is to characterize the 95% horizontal and 95% vertical velocity accuracies during normal maneuvers as specified in RTCA/DO-229D, RTCA/DO-253C, and RTCA/DO-316 receiver MOPS for equipment intended to support either NACV =1 or NACV = 2. Test procedures for higher levels are expected to be developed as more demanding ADS-B applications mature.
d. The tests to verify velocity accuracy performance shall be run for each of the scenarios described below for all operating modes of the receiver where a valid position and/or velocity could be output by the receiver.
(1) It is possible that a given receiver may use a different velocity algorithm when computing an un-augmented GPS position solution versus computing a solution augmented with differential corrections. In that case, this test must be repeated for both the augmented and A4-1
Appendix 4 un-augmented modes of operation. Even in the case where the velocity algorithm is the same whether in un-augmented or augmented mode, there are still enough variables like the software path, inputs, outputs etc., that it is required to repeat the test.
(2) It is not required to repeat the test for different sub-modes of an un-augmented or augmented mode where the inputs, velocity algorithm and outputs are the same.
(3) For GNSS equipment that was not required to meet the current environmental noise standard prescribed by DO-235B, the velocity tests in paragraphs A4-3 through A4-8 use environmental noise test conditions that may cause the equipment to stop functioning. That is, the equipment may lose satellite acquisition and tracking capability causing the equipment to stop outputting velocity. This contributes to an ADS-B availability issue for operators, but loss of function will not prevent the equipment from being used as an ADS-B velocity input provided:
• The equipment does not output misleading velocity information at or after the onset of the triggering interference levels.
Note: A method to accomplish this is first running the test at the higher noise level to ensure there is no misleading velocity information at loss of function before running the complete test at the lower noise level.
• The GNSS equipment manufacturer documents the interference levels that cause the equipment to lose function.
• The GNSS equipment manufacturer factors the lower interference levels into an overall ADS-B availability calculation to be included within the installation instructions.
(4) If the conditions in paragraph A4-2.d(3) are met, the velocity tests in AC 20-138D, Appendix 4 can be run using an environmental noise level that does not cause the equipment to lose acquisition and tracking.
A4-3. Horizontal Velocity Accuracy Test Conditions Commensurate with NACV = 1.
a. Ensure the simulator scenario has enough GPS satellites to provide a horizontal dilution of precision (HDOP) of 1.5 or less.
b. One satellite shall be set at maximum power (including maximum combined satellite and aircraft antenna gain), and the other satellites shall be set at minimum power (including minimum antenna gain).
c. Broadband GNSS test noise (IGNSS,Test) of spectral density as defined in RTCA/DO-229D, paragraph 2.5.8, broadband external interference (Iext,test) and thermal noise contribution from the sky and the antenna (Nsky,antenna) shall be simulated.
A4-2
Appendix 4 Note: In RTCA/DO-229D, paragraph 2.5.8.2 step 2, replace -173.0 dBm/Hz with -172.8 dBm/Hz for total GNSS noise (IGNSS) when running separate GPS/SBAS testing for accuracy verification and/or GPS/SBAS message loss rate data.
d. The airborne equipment shall be initialized with the appropriate position and time. It is assumed that the receiver has obtained a valid almanac for the simulator scenario to be tested prior to conducting the test.
e. Platform dynamics for the horizontal velocity accuracy test shall be as defined in Table 12 below.
Time (s) Dynamics Start Jerk (g/s) End Jerk (g/s) From To North East Down Total North East Down Total 0 T Static 0 0 0 0 0 0 0 0 T+1 T+71 0.58g longitudinal acceleration to 411 m/s
0.xx Note 1
0.xx Note 1 0 0.25 0.xx Note 1
0.xx Note 1 0 0.25 T+72 T+129 Straight un-accelerated flight 0 0 0 0 0 0 0 0 T+130 T+194 -0.45g longitudinal acceleration to 125 m/s
0.xx Note 1
0.xx Note 1 0 0.2 0.xx Note 1
0.xx Note 1 0 0.2 T+195 T+254 Straight un-accelerated flight 0 0 0 0 0 0 0 0 T+255 T+325 turn 180° with 0.58g lateral acceleration
0.xx Note 1
0.xx Note 1 0 0.25 0.xx Note 1
0.xx Note 1 0 0.25 T+326 T+420 Straight un-accelerated flight 0 0 0 0 0 0 0 0 Table 12. Platform Dynamics for Horizontal Velocity Accuracy Test Note 1: The components of the jerk in the north and east
direction depends on the heading chosen in the scenario.
The total jerk is not to exceed the vector combination of
north, east, and down jerk components. The maximum
total jerk to quickly achieve the desired dynamics should be
used, but the jerk should not exceed the normal maneuver
total jerk requirement of 0.25 g/s.
Note 2: The actual times may vary based on the simulator scenario control settings.
A4-3
Appendix 4
f. Signal and radio frequency interference (RFI) conditions can be modified during static period to aid acquisition. Ensure the receiver enters the desired operation mode before dynamics and appropriate signal and interference conditions are applied.
𝑒𝑎𝑠𝑒_𝑒𝑎𝑡𝑒ℎ g. Use the simulator velocity truth data (𝑉𝑎 , 𝑉𝑎𝑛𝑛𝑎𝑒ℎ_𝑒𝑎𝑡𝑒ℎ) and the GNSS 𝑒𝑎𝑠𝑒 receiver velocity data (𝑉𝑎 , 𝑉𝑎𝑛𝑛𝑎𝑒ℎ) to determine the horizontal velocity error ℎ𝑎 after the GNSS receiver has entered the desired navigation mode with the specified signal and RFI conditions:
𝑒𝑎𝑠𝑒_𝑒𝑎𝑡𝑒ℎ − 𝑉𝑎𝑒𝑎𝑠𝑒൯2 𝑛𝑛𝑎𝑒ℎ_𝑒𝑎𝑡𝑒ℎ − 𝑉𝑎𝑛𝑛𝑎𝑒ℎ൯2ℎ𝑎 = ට൫𝑉𝑎 + ൫𝑉𝑎 A4-4. Horizontal Accuracy Pass/Fail Determination.
a. The 95% horizontal velocity accuracy statistic shall be computed using the formula given below. The equipment shall pass if the statistic is less than or equal to 10-LSB m/s.
Note: The notation “10-LSB m/s” specifies that the pass threshold is 10 m/s minus the magnitude of the least significant bit of the output data fields representing the horizontal velocity components. The intent is to ensure that quantization error in the velocity output does not degrade the accuracy below the threshold.
2 ൬1.5(ℎ𝑎)𝑁 ൰ 2 ∗ ඩ∑𝑎=1 𝐻𝐻𝐻𝑅𝑅𝑎 𝑅𝑅 Where:
hi = horizontal velocity error (m/sec).
HDOPi = horizontal dilution of precision at epoch i.
N = number of sample points used.
b. For this test, the number of samples shall include all samples where the receiver is in the desired navigation mode and when in motion.
Note: The minimum number of samples is 420 for a 1 Hz solution and 2100 for a 5 Hz solution (i.e., 5* 420).
A4-5. Horizontal Velocity Figure of Merit Pass/Fail Determination.
The receiver velocity data and the horizontal figure of merit - velocity (HFOMV) data shall be used to determine the percentage of samples bounded by the HFOMV as shown below. The A4-4
- Appendix 4 test passes if TSh,b is greater than or equal to 0.95.
𝑁 1𝑇𝐴ℎ,𝑏 𝑏ℎ,𝑎= 𝑅𝑅 𝑎=1 N = number of samples = ൜1 ℎ𝑎 ≤ 𝐻𝐻𝐻𝐻𝑉𝑏ℎ,𝑎 0 ℎ𝑎 > 𝐻𝐻𝐻𝐻𝑉 A4-6. Vertical Velocity Accuracy Test Conditions Commensurate with NACV = 1.
a. Ensure the simulator scenario has enough GPS satellites to provide a vertical dilution of precision (VDOP) of 3.0 or less.
b. One satellite shall be set at maximum power (including maximum combined satellite and aircraft antenna gain), and the other satellites shall be set at minimum power (including minimum antenna gain).
c. Broadband GNSS test noise (IGNSS,Test) of spectral density as defined in RTCA/DO-229D, paragraph 2.5.8, broadband external interference (Iext,test) and thermal noise contribution from the sky and the antenna (Nsky,antenna) shall be simulated.
Note: In RTCA/DO-229D, paragraph 2.5.8.2 step 2, replace -173.0 dBm/Hz with -172.8 dBm/Hz for total GNSS noise (IGNSS) when running separate GPS/SBAS testing for accuracy verification and/or GPS/SBAS message loss rate data.
d. The airborne equipment shall be initialized with the appropriate position and time.
It is assumed that the receiver has obtained a valid almanac for the simulator scenario to be tested prior to conducting the test.
e. Platform dynamics for the vertical velocity accuracy test shall be as defined in Table 13 below.
A4-5
Appendix 4 Time (s) Dynamics Start Jerk (g/s) End Jerk (g/s) From To North East Down Total North East Down Total 0 T Static 0 0 0 0 0 0 0 0 T+1 T+71 0.58g longitudinal acceleration to 411 m/s
0.xx Note 1
0.xx Note 1 0 0.25 0.xx Note 1
0.xx Note 1 0 0.25 T+72 T+130 Straight and level un-accelerated flight 0 0 0 0 0 0 0 0 T+131 T+131+X Climb, increasing the vertical climb rate from 0 to 21 m/s, then decrease the rate back to 0 m/s and repeat this increasing and decreasing pattern until the time out.
0 0 0.xx Note 1
0.25 0 0 0.xx Note 1
0.25 T+132+X T+192+X Straight and level un-accelerated flight 0 0 0 0 0 0 0 0 T+193+X T+193+2X Descend, increasing the vertical descent rate from 0 to 21 m/s, then decrease the rate back to 0 m/s and repeat this increasing and decreasing pattern until the time out.
0 0 0.xx Note 1
0.25 0 0 0.xx Note 1
0.25 T+194+2X T+274+2X Straight and level un-accelerated flight 0 0 0 0 0 0 0 0 Table 13. Platform Dynamics for Vertical Velocity Accuracy Test Note 1: The components of the jerk in the north and east direction depends on the heading chosen in the scenario.
The total jerk is not to exceed the vector combination of north, east, and down jerk components. The maximum total jerk to quickly achieve the desired dynamics should be used, but the jerk should not exceed the normal maneuver total jerk requirement of 0.25 g/s.
Note 2: The actual times may vary based on the simulator scenario control settings.
Note 3: The value of X must be at least 63 seconds to have enough samples during vertical acceleration.
f. Signal and RFI conditions can be modified during the static period to aid acquisition. Ensure the receiver enters the desired operation mode before dynamics and appropriate signal and interference conditions are applied.
A4-6
Appendix 4
g. Use the simulator velocity truth data (𝑉𝑎𝑣𝑒𝑎𝑒𝑎𝑣𝑎𝑣_𝑒𝑎𝑡𝑒ℎ) and the GNSS receiver velocity data (𝑉𝑎𝑣𝑒𝑎𝑒𝑎𝑣𝑎𝑣) to determine the vertical velocity error (𝑉𝑎) after the GNSS receiver has entered the desired navigation mode with the specified signal and RFI conditions:
𝑣𝑒𝑎𝑒𝑎𝑣𝑎𝑣_𝑒𝑎𝑡𝑒ℎ − 𝑉𝑎𝑣𝑒𝑎𝑒𝑎𝑣𝑎𝑣ห𝑉𝑎 = ห𝑉𝑎 A4-7. Vertical Velocity Accuracy Pass/Fail Determination.
a. The 95% vertical velocity accuracy statistic shall be computed using the formula given below. The equipment shall be considered pass only if the statistic is less than or equal to 50-LSB ft/s.
2 𝑁 ൬ 3(𝑉𝑎) ൰𝑎=1 𝑉𝐻𝐻𝑅𝑅𝑎2 ∗ ඩ∑ 𝑅𝑅 Where:
vi = vertical velocity error (ft/sec).
VDOPi = vertical dilution of precision at epoch i.
N = number of sample points used.
b. For this test, the number of samples shall include all samples where the receiver is in the desired navigation mode.
Note: The minimum number of samples is 420 for a 1 Hz solution and 2100 for a 5 Hz solution.
A4-8. Vertical Velocity Figure of Merit Pass/Fail Determination.
The receiver velocity data and the vertical figure of merit - velocity (VFOMV) data shall be used to determine the percentage of samples bounded by the VFOMV as shown below. The test passes if TSv,b is greater than or equal to 0.95.
𝑁 𝑇𝐴𝑣,𝑏 1 𝑏𝑣,𝑎= 𝑅𝑅 𝑎=1 N = number of samples = ൜1 𝑣𝑎 ≤ 𝑉𝐻𝐻𝐻𝑣𝑏𝑣,𝑎 0 𝑉𝑎 > 𝑉𝐻𝐻𝐻𝑣 A4-7
Appendix 4 A4-9. Additional Tests to Demonstrate Accuracy Commensurate with NACV = 2.
The following procedure is one acceptable means for equipment capable of better accuracy performance to demonstrate compliance with the horizontal velocity error requirement of less than 3 m/s.
a. Run the scenario in Table 13 with all satellites set at high power and no RFI.
b. This accuracy evaluation shall only include those data samples collected during the acceleration period.
c. Find the particular ℎ𝑎 (noted as 𝑇𝑎𝑣𝑣) so that 95% of ℎ𝑎 samples are less than or equal to 𝑇𝑎𝑣𝑣.
d. Re-run the scenario in Table 13 with the same satellite and RFI conditions as the 10 m/s (NACV=1) test.
e. This time only the data samples during the non-acceleration period with the specified signal and RFI conditions are used.
f. Compute:
2 𝑁𝑛𝑛𝑛_𝑎𝑎𝑎 ቆ 1.5൫ℎ𝑎𝑛𝑛𝑛_𝑎𝑣𝑣൯ ඪ∑ 𝐻𝐻𝐻𝑅𝑅𝑎_𝑛𝑛𝑛_𝑎𝑣𝑣ቇ𝑎=1 𝑇𝑛𝑛𝑛_𝑎𝑣𝑣 = 2 ∗ 𝑅𝑅𝑛𝑛𝑛_𝑎𝑣𝑣 Where:
𝐻𝐻𝐻𝑅𝑅𝑛𝑛𝑛_𝑎𝑣𝑣 and 𝑅𝑅𝑛𝑛𝑛_𝑎𝑣𝑣 are the HDOP values for each sample i and the total number of samples (non-acceleration period), respectively.
g. The test passes only if Tacc + Tnon_acc is less than or equal to 3-LSB m/s.
h. The velocity figure of merit is evaluated in the same way as for the 10 m/s test, i.e., the samples during acceleration and non-acceleration periods of the above 2 runs are evaluated together against the 0.95 threshold.
i. The vertical velocity requirement of 15 ft/s should be tested using the exact same philosophy as the test of 3 m/s above but with the scenario in Table 13.
A4-10. Test to Demonstrate HAE Output and Vertical Position Accuracy Metric.
a. The following procedure is one acceptable means for equipment to demonstrate compliance with the HAE and 95% vertical position accuracy output requirements needed to support ADS-B. This parameter is commonly called the vertical figure of merit (VFOM) and A4-8
Appendix 4 should not be confused with the vertical velocity figure of merit (VFOMV) from the velocity accuracy tests. All GNSS TSO equipment should use this test to demonstrate both HAE and 95% vertical position accuracy outputs.
b. The HAE output must be calculated using the general least squares position solution of DO-229D appendix J.1 (or any mathematically equivalent linear combination of range measurements). There is no restriction on the choice of the weight matrix W (including nonweighted solutions), and using the LNAV/VNAV, LP, LPV approach weight (wi = 1/σi2) is optional.
c. The HAE accuracy must be tested using the procedure of DO-229D section 2.5.8.3.
The σi2 used to compute the variance dU2 must be greater than or equal to those listed in appendix J when the equipment uses SBAS-provided integrity and greater than or equal to those listed as an acceptable means for FDE-provided integrity in section 2.1.2.2.2.2 when the equipment does not use SBAS-provided integrity. A fixed sigma of 33.3 m is considered a sufficient over-bound when using FDE-provided integrity. For equipment that uses SBAS- provided integrity, testing only in the highest mode attainable for its declared operational class as specified in the test itself is acceptable.
d. Performing the test described in paragraphs A4-10.a through A4-10.c confirms that the σi and dU used to compute the VFOM accuracy metric provides a sufficient error overbound. The vertical position accuracy metric must be greater than or equal to 1.96 dU where dU is computed using the same σi employed during the HAE accuracy test procedure. This VFOM calculation does not require any specific additional testing.
Note 1: The scaling factors for the vertical position accuracy metric can be rounded to 2 decimal places but there is no intention to prohibit the use of a more accurate number.
Note 2: The vertical position accuracy metric listed above is the standard metric used to provide a minimum of 95% containment under the assumption that a Gaussian distribution with a sigma of σi over-bounds the error of the range measurements. The use of a general least squares position solution (or mathematical equivalent) results in a jointly Gaussian distribution for the components (North, East, Up) of the position error. Any accuracy metric that can be mathematically demonstrated to provide a minimum 95% containment in the position domain under this Gaussian assumption is also acceptable.
A4-11. Test to Demonstrate Horizontal Position Accuracy Metric.
a. The following procedure is one acceptable means for equipment to demonstrate compliance with the 95% horizontal position accuracy output requirements needed to support ADS-B. This parameter is commonly called the horizontal figure of merit (HFOM) and should A4-9
Appendix 4 not be confused with the horizontal velocity figure of merit (HFOMV) from the velocity accuracy tests. TSO-C145/C146 revision ‘b/c’ and TSO-C196(AR) equipment already satisfy this parameter by meeting the TSO requirements. TSO-C145a/C146a and TSO-C129(AR) equipment should use this test to demonstrate the HFOM output.
b. The horizontal position output must be calculated using the general least squares position solution of DO-229D appendix J.1 (or any mathematically equivalent linear combination of range measurements). There is no restriction on the choice of the weight matrix W (including non-weighted solutions), and using the LNAV/VNAV, LP, LPV approach weight (wi = 1/σi2) is optional.
c. The horizontal position accuracy must be tested using the procedure of DO-229D section 2.5.8.3. The σi2 used to compute the variance d2major must be greater than or equal to those listed in appendix J when the equipment uses SBAS-provided integrity and greater than or equal to those listed as an acceptable means for FDE-provided integrity in section 2.1.2.2.2.2 when the equipment does not use SBAS-provided integrity. A fixed sigma of 33.3 m is considered a sufficient over-bound when using FDE-provided integrity. For equipment that uses SBAS-provided integrity, testing only in the highest mode attainable for its declared Operational Class as specified in the test itself is acceptable.
d. Performing the test described in paragraphs A4-11.a through A4-11.c confirms that the σi and dmajor, deast, and dnorth used to compute the HFOM accuracy metric provide a sufficient error over-bound. The accuracy metric must be greater than or equal to 1.96 sqrt(d2east + d2north) or 2.45 dmajor where dmajor, deast, and dnorth are computed using the same σi employed during the horizontal accuracy test procedure. This HFOM calculation does not require any spec ific additional testing.
Note 1: The scaling factors for the horizontal position accuracy metric can be rounded to 2 decimal places but there is no intention to prohibit the use of a more accurate number.
Note 2: The horizontal position accuracy metric listed above is the standard metric used to provide a minimum of 95% containment (varying from 95% to approximately
98.5%) under the assumption that a Gaussian distribution with a sigma of σi over-bounds the error of the range measurements. The use of a general least squares position solution (or mathematical equivalent) results in a jointly Gaussian distribution for the components (North, East, Up) of the position error. Any accuracy metric that can be mathematically demonstrated to provide a minimum 95% containment in the position domain under this Gaussian assumption is also acceptable.
A4-10
Appendix 4 A4-12. Demonstrat ing True Track Angle/True Track Angle Validity.
a. The true track angle/true track validity parameter is intended as a non-critical, optional parameter for airport surface operations. Since most GNSS position sources output some type of track information even during ground operations, it is recommended that GNSS manufacturers output ground track angle as the information can be useful for non-critical ADS B surface applications. The concern is that below a certain velocity the ground track information becomes invalid, and the velocity at which this occurs is dependent upon the specific GNSS equipment design. GNSS/ADS-B integrations at the aircraft level must stop broadcasting ground track when the GNSS ground track information becomes invalid.
Note: It is possible that future ADS-B surface applications may be defined for critical functions. More stringent GNSS performance requirements and tests than what is described below will have to be developed if and when these new surface applications are defined.
b. GNSS equipment not providing a valid ground track.
GNSS manufacturers may choose to not have their equipment provide a ground track output acceptable for the ADS-B true track angle/true track validity parameter. GNSS manufacturers choosing this option need to include a statement within the equipment limitations section that the ground track information must not be used for ADS-B surface applications.
c. GNSS equipment providing a valid ground track for the true track angle/true track validity parameter.
(1) Appendix H in both RTCA/DO-229D and RTCA/DO-316 provides a recommended output for true ground track angle (ARINC 743 all revisions label 103) for those using ARINC 429 characteristics.
(2) GNSS manufacturers must indicate at what velocity the GNSS track angle 95% accuracy (derived from north/east velocity) exceeds eight degrees variance from the aircraft’s actual ground track. GNSS manufacturers must provide this data within the equipment installation instructions for the GNSS/ADS-B integrator.
(3) Optimally, the GNSS equipment will either invalidate or stop outputting the ground track information when it is no longer valid. If the sensor outputs a validity indicator for the velocity, it is sufficient to simply flag the output as invalid if the track accuracy exceeds eight degrees (95%). The GNSS manufacturer must provide information in the installation instructions describing how the sensor outputs the validity indicator if one is provided.
Alternately, it is acceptable for the GNSS manufacturer to state in the installation instructions that the track angle does not meet the required accuracy below a specified velocity and indicate the minimum acceptable velocity.
(4) GNSS manufacturers developing data for the minimum valid velocity should consider the following assumptions:
A4-11