Appendix 3
proceed “Direct-To” the initial fix defining an RF leg segm ent, 2) the aircraft cannot accept a radar vector (a heading assigned by ATC) to the middle of an RF leg segment for intercepting and completing the RF leg segment from that point while sustaining the desired level of performance.
(3) Flight Technical Error (FTE).
System documentation should support maintenance of FTE (95 percent of the flying time) during straight and curved path segments, for each phase of flight and each autopilot and/or FD mode requested. If using FTE values other than those listed in RTCA/DO-283A, the applicant must complete the demonstration in accordance with AC 120-29A, paragraphs 5.19.2.2 and 5.19.3.1.
Note: The applicant may use AC 120-29A, paragraphs
5.19.2.2 and 5.19.3.1 to compute accepted FTE values.
(4) Interface to FGS.
An acceptable autopilot and/or FD response to an RNP system failure or loss must be verified in each autopilot and FD mode, as applicable.
Note: If autopilot malfunction testing was performed for worst case failures, no further validation is required. In this case, the aircraft or equipment manufacturer must provide a statement of confirmation.
(5) Failure Modes/Annunciation.
System documentation should identify any failure modes potentially affecting RNP system RF Leg capability. 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 flightcrew’s primary field of view when loss of navigation capability and/or loss of integrity are experienced.
b. Functional Requirements.
(1) Autopilot and Flight Director.
RNP procedures with RF legs require using an autopilot or FD with at least “roll-steering” capability that is driven by the RNP system. The autopilot/FD must operate with suitable accuracy to track the lateral and, as appropriate, vertical paths required by a specific RNP procedure.
A3-2
Appendix 3
A3-3
(2) Bank Angle.
The flight management computer, the FD system, and the autopilot must be capable of commanding a bank angle up to 25 degrees above 400 feet AGL.
(3) Electronic Map Display.
The aircraft must have an electronic map display depicting the RNP computed path of the selected procedure including RF legs.
(4) Maintaining LNAV in Missed Approach.
If abandoning a procedure while on an RF leg or initiating a go-around or missed approach (through activation of TOGA or other means), the flight guidance mode should remain in LNAV to enable deviation and positive course guidance display during an RF leg. If the aircraft does not provide this capability, crew procedures must be used that assure the aircraft will adhere to the specified flight path during the RF Leg segment.
Note: For missed approaches with an RF Leg, the flightcrew must be able to couple the autopilot or FD to the RNP system (engage LNAV) by 500 feet AGL.
(5) Crew Workload Analysis.
Analyze the crew workload and determine acceptability when flying and monitoring track adherence in association with RF legs during all phases of flight, including those non-normal procedures that can be evaluated in flight.
c. System Approval - Eligibility Airworthiness Documents.
The flight manual or referenced document should contain the following information:
(1) A statement indicating the aircraft meets the requirements for RNP operations with RF legs and has demonstrated the established minimum capabilities for these operations. This documentation should include the phase of flight, mode of flight (e.g., FD on or off and/or autopilot on or off; and applicable lateral and vertical modes), minimum demonstrated RNP value, and sensor limitations, if any.
(2) Any conditions or constraints on path steering performance should be identified
(e.g., autopilot engaged, FD with map display, including lateral and vertical modes, and/or CDI/map scaling requirements). Use of manual control with CDI only is not allowed on RF legs.
(3) The applicant should identify the criteria used for the system demonstration, acceptable normal and non-normal procedures, the demonstrated configurations, type of facilities used, and any constraints or limitations necessary for safe operation.
Appendix 4
Appendix 4. GNSS Tests to Support ADS-B.
A4-1. Introductio
n.
a. The information in this appendix describes bench test procedures that can be used 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, paragraph 7d, states 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 un-augmented modes of operation. Even in the case where the velocity algorithm is the same A4-1
Appendix 4
whether in un-augm ented 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- 138C, 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 R TCA/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) Start Jerk (g/s) End Jerk (g/s) From To Dynamics 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 m odified during static period to aid acquisition. Ensure the receiver enters the desired operation mode before dynamics and appropriate signal and interference conditions are applied.
g. Use the simulator velocity truth data ( trutheast iV _ , truthnorthiV _ ) and the GNSS receiver velocity data ( east iV , northiV ) to determine the horizontal velocity error ih after the GNSS receiver has entered the desired navigation mode with the specified signal and RFI conditions:
2_2_ )()( northitruthnorthieastitrutheastii VVVVh
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.
N i i N i HDOP h 1 2
5.1 *2
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 test passes if TSh,b is greater than or equal to 0.95.
A4-4
Appendix 4
Vi Vi ih N i ihbh HFOMh HFOMhb N bNTS 0 1 samples ofnumber 1 , 1 ,,
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) Start Jerk (g/s) End Jerk (g/s) From To Dynamics 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 A4-6
Appendix 4
appropriate signal and interference conditions are applied.
g. Use the simulator velocity truth data ( truthvertical iV _ ) and the GNSS receiver velocity data ( vertical iV ) to determine the vertical velocity error ( iv ) after the GNSS receiver has entered the desired navigation mode with the specified signal and RFI conditions:
vertical i truthvertical ii VVv _
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.
N i i N i VDOP v 1 2 3 *2
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 bvTS , is greater than or equal to 0.95.
Vi Vi iv N i ivbv VFOMv VFOMvb N bNTS 0 1 samples ofnumber 1 , 1 ,,
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 ih (noted as accT ) so that 95% of ih samples are less than or equal to accT .
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:
accnon N i accnoni accnoni accnon N HDOP h T accnon _ 1 2 __ __ _ _ 5.1 *2
Where:
accnoniHDOP __ and accnonN _ are the HDOP values for each sample i and the total number of samples (non-acceleration period), respectively.
g. The test passes only if accnonacc TT _ 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.
A4-8
Appendix 4
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 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.
A4-9
Appendix 4
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 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 specific 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% A4-10