Chapter 21. Inst alled Performance - Test (RNAV Multi-Sensor Equipment).
21-1. Ground Test.
Refer to TSO-C115b/RTCA/DO-187 or TSO-C115c/RTCA-DO-283A, as appropriate, for RNAV multi-s ensor equipment ground test information.
21-2. Flight Test.
Flight tests are conducted to verify proper operation and accu racy of the multi-sensor equipment as installed in the aircraft (except for GNSS accuracy, see paragraph 20-2). Flight tests should include at least the following:
Note: Required flight evaluations for the first-time airworthiness approval of multi-sensor equipment are accomplished by the cognizant ACO unless specific tests are delegated by the ACO to a flight test pilot designated engineering representative (DER).
a. Evaluation to determine satisfactory EMC between the multi-sensor equipment installation and other onboard equipment (this test may be partially accomplished as a ground test).
b. Validate multi-sensor equipment navigational accuracy in each operating mode. In addition to overall system navigation performance, particular test requirements for navigational accuracy will vary depending upon the particular sensors integrated in the multi-sensor equipment and whether sensor accuracy performance data has previously been obtained. The performance of each navigation sensor should be evaluated separately and in combination with other sensors as applicable.
c. Initial certification for systems including a VOR/DME or multiple (scanning) DME sensor that has not been previously certified must be based upon a demonstration of system accuracy by recording (at not greater than 15 minute intervals) the VOR/DME and/or DME/DME sensor position and comparing it to the actual position during evaluation flights.
The latest revisions of AC 25-7 and AC 23-8 provide guidance on test distances from VOR and DME navigation aids. Recorded data should include sufficient signal parameters and sensor performance data to provide a clear indication of satisfactory sensor performance. The particular flight paths should be selected based upon an analysis of critical signal characteristics, station geometry, signal coverage (including limited station availability with acceptable range), aircraft movement, etc. The system should demonstrate its ability to detect poor signal conditions, inadequate navigation capability, recovery from in-flight power failure, etc. The auto-tune logic should be reviewed and tested to verify that ground stations are identified and tuned correctly.
d. Inertial systems that satisfy the criteria in 14 CFR part 121, appendix G and comply with Table 10 below from RTCA/DO-283A do not need further evaluation. Based on an evaluation of INS/IRU performance, the growth in position error after reverting to INS/IRU can be expected to be less than 2 NM per 15 minutes. Applicants that desire certification credit for 114
better perform ance should coordinate with their ACO for the requirements to demonstrate and document the performance.
Time Since Radio Updating (T) (hr) IRS/IRU 95% Error (NM)
0.0 to 0.5 hr 8*T
0.5 to 1.5 hr 4 Table 10. INS/IRU Accuracy After Loss of Radio Updating
e. Verify navigation data continuity during normal aircraft maneuvering for the navigation modes to be validated (e.g., bank angles of up to 30 degrees and pitch angles associated with approaches, missed approaches and departures).
f. Verify the overall operation of the multi-sensor equipment to include at least the following: the ability to create and modify a flight plan, hold at a designated waypoint, intercept and track to or from a waypoint on a selected course (Course to Fix leg), turn anticipation, waypoint sequencing, selection of an approach and the general presentation of navigational data (depiction of the “TO” waypoint, distance to waypoint, estimated time of arrival, estimated time enroute, ground speed, etc.).
g. Verify that FTE does not exceed 1.0 NM for enroute, 0.5 NM for approach transition and missed approach operating modes, and 0.25 NM for non-precision approach, both with and without autopilot and/or FD use, as applicable. This test may not be necessary if the FTE has been previously established for the aircraft. One acceptable way of assessing FTE is to monitor the measured cross-track deviation while either flying under autopilot control or flying manually using the navigation display provided.
h. If the equipment uses barometric input, verify that the equipment properly interprets the barometer reading. Special consideration should be given to manually entering a barometric correction.
i. Verify/assess all switching and transfer functions, including electrical bus switching, pertaining to the multi-sensor installation. The aircraft system response during any switch over to alternate navigation sources must be evaluated. Particular attention should be given to mode switching and transition requirements associated with the approach mode for equipment incorporating GNSS sensors.
j. Review and verify, where appropriate, various failure modes and associated annunciations, such as loss of electrical power, loss of signal reception, multi-sensor equipment failure, FGS response to GNSS flags, etc. Verify that a warning associated with loss of navigation is accompanied by a visible indication within the pilot’s primary field of view.
21-2.1 Interface to FGS.
a. Evaluate steering response while the FD and/or autopilot is coupled to the multi-s ensor equipment during a variety of different track and mode changes. This evaluation 115
116 should include, as applicable, transition from enroute through the approach to missed approach modes and then back to enroute. Additionally, evaluate all available display sensitivities.
b. Several fly-by turns should be accomplished with varying wind conditions for FD and autopilot. Verify the equipment accomplishes the turn as a fly-by waypoint and discourages overshoot. Fly-by turns are defined as turns where the equipment initiates the turning maneuver prior to sequencing the waypoint by an amount equal to the turn anticipation distance.
c. Verify that the lateral maneuver anticipation supplied by the multi-sensor equipment is appropriate for the aircraft type. Verify that if the multi-sensor equipment is coupled to an autopilot or on approach, an appropriate annunciation of impending waypoint crossing is provided.
d. Verify that execution of the Direct-To function with a resultant aircraft heading change does not overshoot and cause “S” turns that exceed the lateral path tracking FTE requirements.
e. Evaluate the autopilot response to a multi-sensor equipment fault by pulling the circuit breaker for the equipment. This test should be done in each of the sensor modes, if applicable.
21-2.2 GNSS Precision Approach.
a. For equipm ent that provides GNSS precision approach capability, or for equipment with non-standard navigation displays, conduct several approaches while flying raw data, FD only and coupled to the autopilot, as applicable. The objective of the test is to ensure that the multi-sensor equipment interface is compatible with the aircraft and is not a verification of approach performance. This objective is valid only for installations with existing and proven performance (e.g., GNSS providing ILS like deviations to replace or supplement an existing ILS). For installations where the autopilot has been modified or the autopilot lateral/vertical control channel performance has not been assessed, then the approach performance will need to be evaluated per the latest revision of ACs 23-17 or 25.1329-1, or equivalent means.
b. For manual control to the approach flight path, the appropriate flight display(s) must provide sufficient information without excessive reference to other cockpit displays, to enable a suitably trained pilot to maintain the approach path, make alignment with the runway or go-around.
Chapter 22. Inst alled Performance - Test (Baro-VNAV).
22-1. Introduction.
Paragraphs 22-2 and 22-3 describ e the installed performance test considerations for an initial approval. Subsequent installations are addressed in paragraph 22-4. An initial approval refers to the very first time an applicant presents a particular model of baro-VNAV equipment for FAA certification and airworthiness installation approval for an IFR navigation system.
Any new models of baro-VNAV equipment by the same manufacturer should undergo the same approval process as the original equipment unless it can be shown by analysis and test that the new model will function as well or better than the approved equipment.
22-2. Ground Test.
22-2.1 Lab/Bench Tests and Equipment Data Evaluation.
Nor mally the baro-VNAV equipment manufacturer will accomplish these actions for a certification design approval. This phase consists of the following:
a. Analysis of the manufacturer’s procedures for verification and validation of software and review of supporting documentation in accordance with the guidelines of RTCA/DO-178B.
b. Verification of compliance with appropriate environmental qualification standards such as RTCA/DO-160F.
Note: Previously certified baro-VNAV systems may have used an earlier RTCA/DO-160 revision. This equipment may still be installed within the provisions of its original certification.
c. Examination of the equipment’s display capabilities with emphasis on warning, caution, and advisory annunciations.
d. Analysis of failure modes.
e. Review of reliability data to establish that all probable failures are detected.
f. Evaluate the controls, displays, annunciations, and system behavior from a human performance perspective.
g. Review of installation and maintenance manuals.
h. Evaluation of operator's manual (pilot’s guide).
22-2.2 Aircraft Installation Data Evaluation.
Nor mally the baro-VNAV equipment manufacturer will provide an aircraft as a test bed for a first-time installation approval. The first-time installation approval will serve as a 117
basis for subsequent installation approvals on the sam e type of aircraft incorporating the same autopilot/FD system and for other aircraft installations not incorporating autopilot/FD interface with the baro-VNAV equipment. The following assessments must be made:
a. Review the installation drawings, wiring diagram, and descriptive wiring routing.
b. Examine the installed equipment cockpit layout of the with emphasis on equipment controls, applicable circuit breakers (labels and accessibility), switching arrangement and related indicators, displays, annunicators, etc.
c. Analyze the data flow diagram to review which equipment transmits what data to which other equipment.
d. Review the equipment installation structural analysis to ascertain whether all system components are satisfactorily attached to the basic aircraft structure.
e. Examine the electrical load analysis to verify that the system installation’s added electrical power requirements will not cause overloading of the aircraft’s electrical generating capacity.
f. Evaluate the integration with the associated lateral navigation equipment.
22-3. Flight Test.
22-3.1 Functional Flight Test.
a. Evaluate all baro-VNAV equipm ent operating modes.
b. Examine the interface (function) of other equipment connected to the baro-VNAV system.
c. Review various failure modes and associated annunciations, such as loss-of electrical power, loss of lateral navigation signals, baro-VNAV equipment failures, etc.
d. Evaluate steering response while the autopilot is coupled to the baro-VNAV equipment during a variety of lateral and vertical track changes including selection of baro-VNAV modes while operating at the maximum and minimum speeds approved for baro-VNAV use.
e. Evaluate displayed baro-VNAV navigation parameters on interfaced flight deck instruments such as an HSI, CDI, etc.
f. Assess all switching and transfer functions pertaining to the baro-VNAV equipment including high-power electrical loads and electrical bus switching.
g. Evaluate whether magnetic or radio frequency interference exists between the baro-VNAV equipment installation and other onboard equipment, or vice versa.
h. Evaluate the accessibility of all controls pertaining to the baro-VNAV sy stem installation.
i. Evaluate the display(s) and annunciator(s) visibility pertaining to the baro-VNAV system installation during day and night lighting conditions. No distracting cockpit glare or reflections may be introduced.
j. Analyze crew workload and determine acceptability when operating the baro- VNAV equipment.
22-3.2 Navigation Error Flight Test.
a. The initial certification of each baro-VNAV syst em to be used for IFR approach operations should be based on a system performance demonstration by recording the baro-VNAV equipment vertical guidance and comparing it to the actual aircraft position along a pre-established vertical flight path. This evaluation can be made by using:
(1) Theodolite observation;
(2) Comparison against ILS, GPS/SBAS LPV or LNAV/VNAV, or GPS/GBAS GLS glide path signals; or,
(3) By equivalent measuring techniques.
b. Data should be gathered using a variety of descent rates, angles, and lateral navigation source inputs available to the baro-VNAV system.
Note 1: GPS/SBAS LNAV/VNAV most closely emulates baro-VNAV performance.
Note 2: Some baro-VNAV implementations may provide ascent guidance as well for the missed approach segment or for applications other than approach operations. Data should also be gathered for ascent guidance if the equipment provides that capability.
c. The data should demonstrate that the appropriate accuracy criteria of paragraph
10-2.b are met on a 99.7% probability basis.
d. Flights should verify proper operation of caution indications and lateral navigation interface.
e. Normal flight maneuvers should not cause loss of system sensor inputs and the system dynamic response should be confirmed.
f. Evaluate any unusual flight technical errors or errors from using the autopilot and FD.
22-4. Follow-on Approval.
The applicant or installing agency requesting a follow-on baro-VNAV s ystem installation using FAA Form 337 field approval should:
a. Contact either the manufacturer or organization responsible for obtaining the first-time airworthiness approval to:
(1) Obtain a sample AFMS/RFMS (or supplemental flight manual, as appropriate).
(2) Obtain verification of the equipment approval status, including the software program identification and lateral navigation equipment that may be interfaced with the system.
(3) Discuss any problem areas and seek assistance in their solution.
b. Conduct a similar data evaluation as outlined in the paragraph 22-2.2 for baro-VNAV initial approval.
c. Conduct flight evaluations similar to the flight tests outlined in paragraph 22-3.1 for baro-VNAV initial approval.
d. Verify that the maximum expected groundspeed of the aircraft is less than the maximum operating speed for which the baro-VNAV equipment is qualified.
e. Spot check baro-VNAV approach performance by conducting an evaluation flight incorporating at least three ILS approaches comparing baro-VNAV vertical guidance to that provided by the ILS glideslope and three non-precision approaches that normally don’t include vertical guidance (such as LNAV) to a specified minimum descent altitude (not a descent angle).
Note: It is also acceptable to compare baro-VNAV performance to GPS/SBAS LPV or LNAV/VNAV or GPS/GBAS GLS vertical guidance in lieu of ILS.
GPS/SBAS LNAV/VNAV most closely emulates the baro-VNAV performance.
f. Accuracy should be verified by comparison to the ILS glideslope indication and altimeter reading.
g. The purpose of this evaluation flight is not to validate baro-VNAV navigation error values, but rather to verify that, in the course of this installation, nothing was done to compromise the accuracy of the system as determined by the initial approval.
h. Significant differences between the vertical path data provided by the ILS glideslope and/or altimeter and baro-VNAV equipment must be evaluated to determine possible causes. If a logical explanation is not available, additional flight test data points should be collected. If such error(s) persist, installation approval must be withheld.
XX/XX/12 AC 20-138C Appendix 1 Appendix 1. GPS Oceanic/Remote Navigation.
A1-1. GPS Ocean ic/Remote Navigation.
a. The following criteria define an acceptable means of compliance for approval of TSO-C129(AR) GPS equipment intended for oceanic and remote operation without reliance on other long-range navigation systems. This approval is granted as a non-TSO function according to existing policy. Equipment that previously demonstrated compliance to Notice 8110.60 or AC 20-138A, appendix 1 are still eligible for oceanic and remote operation and need not be re-evaluated.
Note: TSO-C129a has been cancelled but equipment with an existing TSO-C129a TSOA may receive approval for Class II oceanic and remote operation without reliance on other long range navigation systems.
b. TSO-C196(AR) and TSO-C145/C146(AR) equipment are inherently capable of supporting this operation without further evaluation if the operator obtains a FDE prediction program (see paragraph 5-2.3). Equipment manufacturers may choose to provide further robustness for oceanic and remote area operations by including barometric aiding in their FDE algorithms. Appendix G of RTCA/DO-316 and RTCA/DO-229D provide an acceptable barometric aiding implementation method for TSO-C196(AR) and TSO-C145/C146(AR) equipment respectively.
Note: Barometric aiding enables the equipment to continue providing integrity when only four satellites are available for use in the position solution. Appendix G of RTCA/DO-229C for TSO-C145a/C146a equipment is identical to appendix G in RTCA/DO-229D.
A1-2. Approval Process
a. TSO Authorization.
The criteria in this appendix are in addition to the TSO-C129(AR) requirements and approved as a non-TSO function. The ACO should issue a separate letter of design approval stating that the equipment (including part number) and software prediction program (including revision number) meet the criteria in this appendix. The applicant should be able to substantiate equivalent performance between the FDE prediction program and the airborne receiver algorithm. See paragraph 5-2.3 for information on FDE prediction program performance.
b. Installation Approval.
(1) The applicant obtains the GPS navigation equipment installation approval.
(2) If the equipment manufacturer has previously obtained a letter of design approval as described in paragraph A1-1.a of this appendix, further evaluation as described in A1-1
XX/XX/12 AC 20-138C Appendix 1 paragraphs A1-2 and A1-3 of this appendix is not required.
(3) If the equipm ent manufacturer has not obtained a letter of design approval, then the applicant must demonstrate compliance with the requirements in paragraphs 2 and 3 of this appendix.
(4) The failure of the long-range navigation function is a major failure condition.
For many oceanic/remote operations, this requires equipping the airplane with at least two (or more) independent (i.e., dual control display unit, dual GPS antenna, dual power sources, dual GPS sensors, etc.) navigation equipment with a mean time between failures of at least 1000 hours each (for dual equipage).
(5) Once the installation has been approved, the AFMS/RFMS should be updated to state: "The XXX GPS equipment as installed has been found to comply with the requirements for GPS Class II oceanic and remote navigation without reliance on other long-range navigation systems when used in conjunction with the XXX prediction program. This does not constitute an operational approval."
Note: The term “primary means” is obsolete. This updated AFMS/RFMS language is a clarification of previous guidance.
c. Operational Approval.
The applicant should be aware that an operational approval must be obtained before conducting Class II navigation (remote/oceanic). Applicants should contact the appropriate flight standards district office to seek operational approval.
A1-3. Equipment Performance.
a. TSO-C129(AR).
The GPS equipment must have an existing TSO-C129(AR) TSOA.
b. Fault Detection and Exclusion.
(1) The GPS equipment must be able to detect and exclude a GPS satellite failure by means of an FDE algorithm. The exclusion of a satellite failure must be automatic; pilot action is not permitted to accomplish exclusion. Additional augmentations (such as clock aiding or barometric aiding) are not precluded if equipment manufacturers choose to implement these methods to increase FDE robustness. FDE terms are defined in RTCA/DO-316, and RTCA/DO-316 appendix G provides an acceptable barometric aiding implementation method.
(a) Missed alert probability. The probability of missed alert must be less than or equal to 0.001 for every geometry and every navigation mode. This requirement is on the missed alert rate external to the GPS equipment. When related to the internal algorithm, it includes both probabilities of missed detection and false exclusion.
A1-2
XX/XX/12 AC 20-138C Appendix 1
(b) False a lert probability. The probability of false alert must be less than or equal to 0.002/hour. This requirement is on the false alert rate external to the GPS equipment.
When related to the internal algorithm, it includes both probabilities of false detection and the failure to exclude the false detection.
(c) Failed exclusion probability. The probability of failed exclusion must be less than or equal to 0.001 for every geometry and every navigation mode for which exclusion is implemented. Exclusion must be implemented for the oceanic mode. This requirement is on the alert rate external to the GPS equipment due to failed exclusion.
(d) Time-to-alert. The time-to-alert for oceanic/remote navigation mode is defined to be at least 30 seconds, but must not exceed 5 minutes.
(2) In addition to FDE, the equipment must use an acceptable means to detect and exclude from the navigation solution any satellite that experiences a failure which causes a pseudorange step. A pseudorange step is a sudden change in the measured distance to a satellite. It can be written as:
PRSTEP = | PRPREDICTED - PRMEASURED |
where PRPREDICTED is the predicted pseudorange at the time of measurement, based on previous measurements, and PRMEASURED is the pseudorange at the time of the measurement.
(a) The equipment must detect a pseudorange step error greater than 1000 meters, including steps that cause loss of lock for less than 10 seconds.
(b) If a pseudorange step is detected for a satellite, that satellite must be excluded from use in the navigation algorithm until its integrity can be verified and fault detection is available. The equipment manufacturer is free to choose any method to calculate the predicted pseudorange. However, any method used should properly take into account satellite movement and aircraft dynamics up to a groundspeed of 750 knots (kts) and accelerations up to 14.7 meters/second/second (1.5 g's).
(3) The GPS equipment must exclude, without pilot action, any satellite designated unhealthy by any of the GPS navigation data. The satellite must be excluded within 5 minutes of the designation as unhealthy by the satellite. RTCA/DO-316, paragraph 2.1.1.3.2 provides a description of the parameters that must be checked.
(4) If a GPS satellite failure results in loss of GPS navigation (due to the failure to exclude or due to loss of a critical satellite), an appropriate failure indication must be provided to the flight crew.
(5) It is recommended that the equipment provide, upon request, an indication of the current estimate of position uncertainty in nautical miles.
(a) This estimate must be based on measurement inconsistency and must bound the true error with high confidence (approximately 99.9 percent).
A1-3
XX/XX/12 AC 20-138C Appendix 1 A1-4
(b) This estimate will not be available if there are only four measurements available (because there is no redundancy).
(c) This position uncertainty estimate is equivalent to the Horizontal Uncertainty Level (HUL) that is an optional output for TSO-C196(AR) and TSO-C145(AR)/C146(AR) equipment, and provides the most time for the exclusion algorithm to exclude the failure without increasing the probability of a missed alert.
(d) This output is intended to provide information about the approximate magnitude of a potential positioning failure, when the horizontal protection level exceeds the alert limit or when a positioning failure has been detected, but not excluded.
Appendix 2
Appendix 2. RNP AR Operations.
A2-1. Introductio
n.
a. This appendix describes the aircraft performance, functional criteria, and installation considerations for aircraft to qualify for RNP AR approaches. The aircraft qualification information is presented here as a convenient necessary first step to consolidate all the positioning and navigation equipment and RNP AR airworthiness guidance into one AC. The information presented in this appendix has some necessary minor changes due to formatting and grammar along with some additional clarification information. But, the basic information from AC 90-101A has not changed other than to recognize TSO-C196(AR) equipment. The plan is for future AC 90-101 revisions to remove the airworthiness guidance. See the latest revision of AC 90-101 for operational approval guidance information.
b. Applicants may establish compliance with this appendix as part of a type certification or supplemental type certification and document this in the aircraft flight manual (supplement). The TC holder of a previously certified aircraft can document compliance with these aircraft qualification criteria without a new airworthiness project (e.g., without AFM/RFM change), and should advise the appropriate ACO of any new performance the original airworthiness approval did not cover. The AFM/RFM or other aircraft qualification evidence should address: the required modes of operation to fly an RNP AR approach; the normal and abnormal flight crew operating procedures; responses to failure alerts and annunciations; and any other operating limitations.
c. For aircraft with ILS capability that is interfaced to GPWS or Class A TAWS (Mode 5 GPWS) alert, the FAA recommends that RNP AR airworthiness applicants (i.e., the TC or STC holder) include a glidepath alerting function for excess deviation below glidepath similar to a GPWS or Class A TAWS (Mode 5 GPWS) alert for ILS deviations below the ILS glideslope. The intent for this function is to adopt the safety benefits of the ILS glideslope alert by including a similar alert during RNP AR approaches for deviations below the final approach segment glidepath. However, the function need not be accomplished through the GPWS or TAWS equipment, although using the GPWS or TAWS equipment is certainly acceptable. The use of alerting for flight technical error or total system error can also meet this functional guidance. GPS/SBAS vertical performance monitoring and alerting is also acceptable to meet this functional guidance if GPS/SBAS is implemented for RNP AR approaches.
Note: The applicant (i.e., TC or STC holders) should be cognizant of the existing alerts on the aircraft when implementing the baro-VNAV alert function. The alert function should not conflict with existing alerts or cause flightcrew human factors issues.
(1) The glidepath function should provide alerts similar to a GPWS/TAWS alert during ILS operations that occurs at 1.3 dots deviation low scaling. The FAA recognizes that performance scales for baro-VNAV may not match the ILS deviation scaling; particularly for non-temperature compensated equipment. It is acceptable for applicants to provide an alert when the below glidepath deviation exceeds 75 ft (i.e., the baro-VNAV FTE lim its for approach A2-1