Chapter 23. Installed Performance - Test (Baro-VNAV).
23-1. Introduction.
Paragraphs 23-2 and 23-3 describe the installed performance test considerations for an initial approval. Subsequent installations are addressed in paragraph 23-4. 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.
23-2. Ground Test.
23-2.1 Lab/Bench Tests and Equipment Data Evaluation.
Normally 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 or ‘C’.
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).
23-2.2 Aircraft Installation Data Evaluation.
Normally the baro-VNAV equipment manufacturer will provide an aircraft as a test 150
bed for a first-time installation approval. The first-time installation approval will serve as a basis for subsequent installation approvals on the same 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 with emphasis on equipment controls, applicable circuit breakers (labels and accessibility), switching arrangement and related indicators, displays, annunciators, 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.
23-3. Flight Test.
23-3.1 Functional Flight Test.
a. Evaluate all baro-VNAV equipment 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. E valuate how distance to go, course, bearing, etc. are displayed on all flight deck presentations during approach procedures when step-down fixes are included in the navigation database (see paragraphs 12-8 and 18-2.b).
f. If equipped, when temperature compensation is enabled ensure that the display of corrected altitude(s) is consistent on all displays in the cockpit.
g. Assess all switching and transfer functions pertaining to the baro-VNAV equipment including high-power electrical loads and electrical bus switching.
h. Evaluate whether magnetic or radio frequency interference exists between the baro-VNAV equipment installation and other onboard equipment, or vice versa.
i. Evaluate the accessibility of all controls pertaining to the baro-VNAV system installation.
j. 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.
k. Analyze crew workload and determine acceptability when operating the baro- VNAV equipment.
23-3.2 Navigation Error Flight Test.
a. The initial certification of each baro-VNAV system 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 the actual coded path and appropriate path definition.
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. See paragraph 18-5 for a description of GPS/SBAS versus baro-VNAV differences.
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
11-2.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.
23-4. Follow-on Approval.
The applicant or installing agency requesting a follow-on baro-VNAV system 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 23-2.2 for baro-VNAV initial approval.
c. Conduct flight evaluations similar to the flight tests outlined in paragraph 23-3.1 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, GPS/SBAS 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 153
a logical explanation is not available, additional flight test data points should be collected. If such error(s) persist, installation approval must be withheld.
Appendix 1 Appendix 1. GPS Oceanic/Remote Navigation.
A1-1. GPS Oceanic/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 previous revisions of AC 20-138, appendix 1 are still eligible for oceanic and remote operation and do not need re-evaluation.
Note 1: TSO-C129a has been cancelled but equipment with an existing TSO-C129a TSOA may receive approval for oceanic/remote operation without reliance on other long range navigation systems.
Note 2: The FAA has adopted the ICAO term
“oceanic/remote” instead of Class II.
b. TSO-C196(AR) and TSO-C145/C146(AR) equipment are inherently capable of supporting this operation without further evaluation if the operator obtains an 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, Change 1 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, Change 1.
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.
A1-1
Appendix 1
(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 paragraphs A1-2 and A1-3 of this appendix is not required.
(3) If the equipment manufacturer has not obtained a letter of design approval, then the applicant must demonstrate compliance with the requirements in paragraphs A1-2.b(4) through A1-3 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 oceanic/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 1: The term “primary means” is obsolete. T his updated AFMS/RFMS language is a clarification of previous guidance.
Note 2: The FAA has adopted the ICAO term
“oceanic/remote” instead of Class II.
c. Operational Approval.
The applicant should be aware that an operational approval must be obtained before conducting oceanic/remote navigation. 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.
A1-2
Appendix 1
(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.
(b) False alert 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.
A1-3
Appendix 1
(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).
(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.
A1-4
Appendix 2 Appendix 2. RNP AR Operations.
A2-1. Introduction.
a. This appendix describes the aircraft performance, functional criteria, and installation considerations for aircraft to qualify for RNP AR approaches. The information presented in this appendix has some necessary changes, mostly due to formatting and grammar, but also provides additional clarification information. This AC will take precedence for aircraft qualification if there are any perceived conflicts with the latest revision of AC 90-101. 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. FAA headquarters retains oversight of all applications for operations approval to conduct RNP AR operations. To avoid delays in processing these operations applications and confirming aircraft qualification, Aircraft Certification field offices should coordinate all RNP AR aircraft qualification airworthiness applications with the Navigation and Flight Technologies section (AIR-131) at FAA headquarters. Coordinating the application with AIR-131 will ensure the aircraft qualification requirements are met and documented in a manner facilitating an applicant's expeditious RNP AR operations approval.
d. The FAA strongly recommends RNP AR airworthiness applicants (i.e., the TC or STC holder) include a deviation alerting function for excess lateral or vertical deviation during RNP AR approach operations. The intent for this function is to prevent controlled flight into terrain or obstacles during RNP AR operations.
Note 1: This recommendation applies whether the aircraft uses baro-VNAV vertical guidance or GPS/SBAS vertical guidance during RNP AR approach operations.
Note 2: Aircraft with existing, approved deviation alerting functions supporting RNP AR approach operations in service prior to 2016 meet the intent of this guidance.
(1) The deviation alerting function need not be accomplished through the aircraft’s GPWS or TAWS equipment, as this may not be practical from a systems engineering perspective. Applicants may base the alert on flight technical error or total system error .
(2) The FAA recommends applicants provide an alert no later than when a A2-1
--- --- Appendix 2 deviation reaches operational deviation limits for RNP AR approach operations. An alert should occur when a glidepath deviation reaches or exceeds 75 feet; or when a lateral deviation reaches or exceeds a distance equivalent to one times the RNP value in use (i.e., 1×RNP).
More conservative alerting schemes are acceptable.
(3) The deviation alert should occur within 10 seconds of reaching a lateral or vertical deviation limit consistent with the RNP AR procedure design assumptions.
(4) The deviation alert may be aural, visual or both. The alert should be easily recognized by the pilot; and, when the implementation uses a visual alert, the visual alert should be in the pilot’s primary field of view.
Note: The airworthiness applicant should be cognizant of the existing alerts on the aircraft when implementing the deviation alerting function. The deviation alerting function should not conflict with existing alerts or cause flight crew human factors issues. The deviation alerting should not supersede and prevent initiation of other mandatory alerting functions.
e. The RNP AR airworthiness applicant (i.e., the TC or STC holder) should consider developing: an operations manual detailing flight crew/pilot procedures for executing RNP AR operations; detailed suggestions on training for RNP AR operations; and any necessary maintenance plan(s) for the aircraft to enable ongoing RNP AR operations. The applicant should complete these concurrent with the airworthiness approval to assist operators with their RNP AR operations approval. Use of these standardized products could streamline the operator’s RNP AR operational approval. See the latest revision of AC 90-101 for operational approval information.
f. In addition to the specific RNP AR guidance in this appendix, the aircraft’s positioning and navigation system(s) must comply with the applicable chapters in this AC.
A2-2. Performance Requirements.
This paragraph defines the general performance requirements for aircraft qualification.
Paragraphs A2-3, A2-4, and A2-5 of this appendix provide guidance material on an acceptable means of satisfying these requirements.
a. Path Definition.
The published instrument approach procedure defines the path the aircraft must use to evaluate performance. The aircraft’s navigation system will also define the vertical path in the final approach segment by a flight path angle and as a straight line emanating from a fix and altitude.
A2-2
Appendix 2
b. Lateral Accuracy.
The navigation system must provide lateral guidance so aircraft remain within the lateral boundaries of the defined RNP AR procedure at one times the RNP value in use (1×RNP, 95%).
c. Vertical Accuracy.
The vertical system error includes altimetry system error (assuming the temperature and lapse rates of the International Standard Atmosphere), the effect of along-track error, system computation error, data resolution error, and flight technical error. The 99.7% of system error in the vertical direction must be less than the following (in feet):
ඥ[(6076.115)(1.225)𝑅𝑅𝑅𝑅𝑅𝑅 tan 𝜃𝜃]2 + (60 tan 𝜃𝜃)2 + 752 + [(−8.8 × 10−8)(ℎ + ∆ℎ)2 + (6.5 × 10−3)(ℎ + ∆ℎ) + 50]2 where θ is the vertical navigation path angle, h is the height of the local altimetry reporting station and ∆h is the height of the aircraft above the reporting station.
d. Airspace Containment.
The FAA publishes RNP AR approaches as performance-based approaches. As such, they do not inherently require any specific technology or procedure, but instead require a level of performance.
(1) RNP AR and baro-VNAV.
Establishing compliance to a required level of performance can be difficult. This appendix describes an acceptable means of achieving the required navigation performance.
This appendix provides a detailed acceptable means of compliance for aircraft using an RNAV system relying primarily on GNSS and a VNAV system relying on barometric altimetry.
Aircraft complying with this appendix provide the requisite airspace containment.
(2) Other Systems or Alternate Means of Compliance.
The probability of the aircraft exiting the lateral and vertical extent of the obstacle clearance volume must not exceed 10-7 per approach, including the missed approach. An operator may satisfy this requirement through an operational safety assessment applying:
(a) Appropriate quantitative, numerical methods,
(b) Qualitative operational and procedural considerations and mitigations, or
(c) An appropriate combination of both quantitative and qualitative methods.
Note 1: If the aircraft does not remain within the obstacle clearance volume after annunciating the systems failure, then this requirement applies to the total probability of A2-3