Appendix C — Installation and testing guidance

ED Decision 2019/011/R

(1)     Introduction

(a)      Appendix C provides guidance on the installation and testing of RNP Systems. Depending on the applicable airworthiness standards, the applicant should consider the following paragraphs as indicated below:

(i)      Paragraphs (2), (3), and (4) of Appendix C should always be considered.

(ii)     When Subsection 3 ‘Supplementary specifications for lateral navigation in final approach’ is applicable, paragraph (5) ‘Supplementary testing for lateral navigation in final approach’ of Appendix C should be considered.

(iii)     When Subsection 4 ‘Supplementary specifications for vertical navigation’ is applicable, paragraph (6) ‘Supplementary testing for vertical navigation’ of Appendix C should be considered.

(iv)     When Subsection 5 ‘Supplementary specifications for vertical navigation in final approach’ is applicable, paragraph (7) ‘Supplementary testing for vertical navigation in final approach’ of Appendix C should be considered.

(v)      When Subsection 7 ‘Supplementary specifications for applications for advanced RNP’ is applicable, paragraph (8) ‘Supplementary testing for applications for advanced RNP’ of Appendix C, as well as Appendix D ‘RF leg demonstration templates’, should be considered.

(2)     Equipment installation

(a)      The applicant should can use equipment that has been granted ETSO authorisation and, in that case, should strictly follow the equipment manufacturer installation guide.

(b)     For each of the equipment installed, the applicant should verify and assess all switching and transfer functions, including electrical bus switching and failure modes under partial or complete loss of electrical power, loss of signal reception, loss of equipment interfaced with the RNP system, etc. Under such failure conditions, the applicant should:

(i)      evaluate the aircraft’s system response to ensure that the switch is accomplished as expected;

(ii)     verify that the switch is clearly enunciated and that any warning associated with the loss of equipment is commensurate with the requirements of CS XX.1322; and

(iii)     verify that the switching itself does not induce any inaccurate guidance and that the autopilot/flight director response is appropriate.

(c)      For a multi-sensor installation, under sensor failure conditions, the applicant should verify the following:

(i)      that the GNSS is used as a primary source of navigation;

(ii)     the transfer to an alternative navigation sensor and the appropriate switching mode and annunciation are made;

(iii)     that the switch is clearly enunciated and that any warning associated with the loss of equipment is commensurate with the requirements of CS XX.1322;

(iv)     that the switching itself does not induce any inaccurate guidance and that the autopilot/flight director response is appropriate; and

(v)      that the remaining navigation sensors are appropriately reflected in the positioning computation of the RNP system.

(d)     During simulated loss of the GNSS signal-in-space, the applicant should verify that the criteria of point (2)(c)(ii) to (2)(c)(v) are met.

(e)     Initial certification of systems, including multiple (scanning) DME sensors that have not been previously certified, must be based upon a demonstration of system accuracy by recording (at intervals not greater than 15 minutes) the DME/DME sensor position and comparing it to the actual position during evaluation flights. The latest revisions of FAA AC 25-7D and FAA AC 23‑8C 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 applicant should select the particular flight paths based on 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 applicant should review and test the auto-tune logic to verify that ground stations are identified and tuned correctly.

(f)      Inertial systems that satisfy the criteria of Appendix B do not need further evaluation.

(g)      With regard to GNSS sensors that have been granted an ETSO authorisation against ETSO‑C146 (Class Gamma equipment), it is stipulated that the equipment will support installations with the ability to compensate for the navigation centre to antenna offset. If applicable, the applicant should confirm that the antenna to aircraft centre of navigation offset is appropriate to the installation for GNSS SBAS equipment supporting RNP APCH to LPV and LNAV/VNAV minima.

Note: The fact that the GNSS antenna is top-mounted can result in several feet of vertical difference between the antenna and the aircraft centre of navigation, significantly greater than for ILS antennas. The centre-of-navigation to wheel-crossing height should be evaluated for each installation. For most installations, a fixed vertical offset is adequate.

(h)     The applicant should evaluate the accessibility of all controls pertaining to the installation of the RNP System.

(i)      The applicant should evaluate the visibility of display(s) and annunciator(s) pertaining to the installation of the RNP System during day and night lighting conditions. No distracting cockpit glare or reflections may be introduced.

(3)     Sensor interference testing

(a)      GNSS equipment is particularly susceptible to out-of-band SATCOM emissions and in-band inter-modulation between multiple channel SATCOM installations. The applicant should not install GNSS equipment on aircraft with SATCOM transceivers, unless absence of interference with the GNSS sensor is demonstrated.

(b)     Improperly used or installed GNSS re-radiators can present misleading information to GNSS equipment. Equipment manufacturers may provide mitigation against the use of erroneous data for GNSS position and navigation solutions. Possible measures include: implementing or enabling cross-checks of GNSS sensor data against independent position sources and/or other detection monitors using GNSS signal metrics or data. It is left to the applicant to determine that the method chosen by the equipment manufacturer is adequate for the aircraft integration.

(c)      The applicant should demonstrate the lack of interference from VHF radios on the completed installation of navigation sensors (GNSS, DME where applicable, etc.) by tuning each VHF transmitter to the frequencies listed below and transmitting for a period of 30 seconds while observing the signal status of each satellite being received. Degradation of individually received satellite signals below a point where the satellite is no longer available will require additional isolation measures to be taken:

(i)      121.150 MHz; 121.175 MHz; 121.200 MHz; 131.250 MHz; 131.275 MHz; and 131.300 MHz (for radios with 25-kHz channel spacing); and

(ii)     121.185 MHz; 121.190 MHz; 130.285 MHz and 131.290 MHz (for radios with 8.33-kHz channel spacing);

(d)     For installations on rotorcraft, the applicant should ensure that the rotor blades do not interfere with the received signals. This problem has been experienced in some rotorcraft and varies with the rotation rate.

(4)     Generic testing for performance-based lateral navigation

(a)      The applicant should evaluate the navigation parameters displayed on cockpit instruments (such as HSI, CDI, distance display, electronic flight instrument system, moving maps, FMSs, etc.) against the relevant criteria. In particular, the parameters displayed should be consistent across the cockpit, especially the aircraft heading or track reference (magnetic or true), the aircraft altitude (feet or metres), and the aircraft speed (knots or km/h).

(b)     The applicant should verify that the RNP system continuously provides to the flight crew:

(i)      an estimation of the present position, the position accuracy and integrity;

(ii)     the computed desired path and the deviation from that path; in particular, the applicant should:

(1)     evaluate the sensitivity of the deviation display;

(2)     verify that the full-scale setting is appropriate for the intended operation; and

(3)     when applicable, verify that when the full-scale setting changes, the display of the updated deviation is appropriate;

(iii)     the identification of the active TO waypoint;

(iv)     the distance, bearing and time to the active TO waypoint; and

(v)      the aircraft ground speed.

This behaviour should be evaluated for different flight phases, altitudes, and under various normal aircraft manoeuvres (e.g. bank angles of up to 30 degrees and pitch angles associated with take-off, departures, approaches, landing, and missed approaches, as applicable).

(c)      The applicant should verify that the course selector and the RNP system are properly integrated. The behaviour of the system and the display of the aircraft heading and the selected course should be appropriate and consistent when the aircraft follows the RNP system’s flight plan but also when the aircraft is manually flown.

(d)     The applicant should verify the automatic and manual selection/deselection of sensor types and positioning aids, in particular:

(i)      The appropriate automatic sensor selection should be verified, and, where a multi-sensor system is installed, the applicant should check that the automatic selection is consistent with GNSS being the primary source of horizontal position;

(ii)     Where a multi-sensor system is installed, the applicant should verify the appropriate automatic reversion when one or several sensors fail;

(iii)     The applicant should verify the appropriate automatic selection and tuning of positioning navigation aids. Where DME is installed, the automatic selection and tuning should be evaluated where multiple DME can be received from the aircraft, for different flight phases and different altitudes. For each sensor, the applicant should verify the continuous aircraft position estimations for different flight phases, altitudes, and various normal aircraft manoeuvring (e.g. bank angles of up to 30 degrees and pitch angles associated with take-off, departures, approaches, landing and missed approaches as applicable);

(iv)     The applicant should check the capability to manually override the selection or deselection of a positioning sensor type and positioning navigation aids.

(e)     The applicant should verify the capability to create, review, modify and activate a flight plan. In particular, the applicant should verify the capability to extract and load procedures from the navigation database into the RNP system. During the extraction, all procedures’ characteristics (sequence of waypoints, speed and/or altitude constraint, etc.) should be loaded into the flight plan.

(f)      The applicant should evaluate the following aspects when the RNP system is interfaced with an autopilot and/or a flight director. If some issues are raised, the RNP system may still be installed, but either should not be connected to the autopilot or have an appropriate aircraft flight manual supplement/rotorcraft flight manual supplement (AFMS/RFMS) limitation that mitigates the issue.

(i)      The applicant should evaluate the steering response while the flight director and/or autopilot are/is coupled to the RNP system during a variety of different track and mode changes while operating at the maximum and minimum operating speeds. This evaluation should include, as applicable:

(1)     transition from en route through the approach to missed approach modes and then back to en route;

(2)     intercept and track to and from a waypoint on a selected course.

(ii)     The applicant should evaluate:

(1)     the steering response during the automatic sequencing of various flight plan legs and transition; and

(2)     the appropriate display of this sequencing to the flight crew.

In particular, the capability to execute fly-by, fly-over, and RNAV holding should be evaluated for different altitudes, wind conditions, aircraft speeds, and configurations.

(iii)     The applicant should verify that the lateral manoeuvre anticipation supplied by the RNP system is appropriate for the aircraft type. The applicant should verify that an appropriate annunciation of impending waypoint crossing is provided.

(iv)     The applicant should verify that execution of the ‘direct-to’ and ‘direct-to’ with intercept function with a resultant aircraft heading change do not overshoot and do not cause ‘S‑turns’.

(v)      The applicant should evaluate that the autopilot response to the RNP system fault by simulating a representative fault consistent with the equipment architecture (e.g. pulling the circuit breaker). This test should be done under various navigation modes.

(vi)     The applicant should verify that modification of the flight plan does not impact on the aircraft guidance until the flight plan and its modification is activated. This behaviour should be evaluated for various kinds of flight plan modifications (lateral revision, constraint insertion/deletion, etc.) and for different procedure types (departure procedures, en route, manually inserted segment, arrival procedures, etc.).

(g)      The applicant should verify that the flight technical error (FTE) does not exceed the FTE credits. This test may not be necessary if the FTE has been previously established for the aircraft concerned. 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)     Tests should verify proper operation of caution indications and lateral navigation interface.

(i)      Normal flight manoeuvres should not cause loss-of-system sensor inputs and the system dynamic response should be confirmed.

(j)      The applicant should validate the navigational accuracy of multi-sensor equipment in each operating mode. In addition to overall system navigation performance, particular test requirements for navigational accuracy will vary depending on 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.

(5)     Supplementary testing for lateral navigation in final approach

(a)      For installations where the autopilot has not been modified and the RNP system provides ILS-like deviations, the applicant should conduct several approaches:

(i)      while flying raw data, flight director, and coupled to the autopilot, as applicable;

(ii)     while intercepting before and after the final approach fix (FAF),

and check that the autopilot response is appropriate and that the displays are appropriate and consistent within the cockpit.

The objective of this test is not to verify approach performance but to ensure that the RNP system interfaces are compatible with the aircraft. In addition, the autopilot approach functionality should be evaluated to ensure compatibility with the ‘gain scheduling’ employed by some autopilots during approaches.

(b)     For installations where the autopilot has been modified, the autopilot lateral control channel performance has not been assessed, or non-standard deviations are provided (not ILS-like), the approach performance will need to be evaluated by the applicant as per the latest revision of, AMC1 to CS 25.1329, FAA AC 23-17C or FAA AC 29-2C.

(c)      For manual control to the approach flight path, the applicant should demonstrate that the appropriate flight display(s) provide(s) sufficient information to maintain the approach path and align with the runway or go-around without excessive reference to other cockpit displays.

(d)     In order to ensure the system operates properly, the applicant should evaluate the lateral full-scale deflection while on approach.

(e)     The applicant should evaluate 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.

(6)     Supplementary testing for vertical navigation

(a)      The applicant should evaluate the autopilot response to the insertion of various altitude constraints into the RNP system’s flight plan:

(i)      ‘AT or BELOW’ altitude constraint;

(ii)     ‘AT or ABOVE’ altitude constraint;

(iii)     ‘AT’ altitude constraint;

(iv)     ‘WINDOW’ altitude constraint.

The autopilot response should be evaluated under various conditions (different aircraft configurations and speeds, different lateral paths, and transitions at the altitude constraint, etc.).

(7)     Supplementary testing for vertical navigation in final approach

(a)      For installations where the autopilot has not been modified and the RNP System provides ILS-like deviations, the applicant should conduct several approaches:

(i)      while flying raw data, flight director and coupled to the autopilot, as applicable;

(ii)     while intercepting before and after the final approach fix (FAF),

and check that the autopilot response is appropriate and that the displays are appropriate and consistent within the cockpit.

The objective of this test is not to verify approach performance, but to ensure that the RNP system interfaces are compatible with the aircraft. In addition, the autopilot approach functionality should be evaluated to ensure compatibility with the ‘gain scheduling’ employed by some autopilots during approaches. For example, some autopilots depend upon a radio altimeter or middle marker beacon passage inputs to enable a ‘glideslope extension’ function to reduce oscillating or aerodynamic instability when coupled to a glideslope signal during the final approach phase. As PBN approaches do not have middle marker beacons, the autopilot response needs to be evaluated when incorporating the PBN capability.

(b)     For installations where the autopilot has been modified, the autopilot lateral control channel performance has not been assessed, or non-standard deviations are provided (not ILS-like), then the approach performance will need to be evaluated by the applicant as per the latest revision of AMC1 to CS 25.1329, Appendix B of CS-29, FAA AC 23-17b or equivalent means.

(c)      For manual control to the approach flight path, the applicant should demonstrate that the appropriate flight display(s) provide(s) sufficient information to maintain the approach path and align with the runway or go-around without excessive reference to other cockpit displays.

(d)     In order to ensure that the system operates properly, the applicant should evaluate the vertical full-scale deflection while on approach.

(e)     A flight crew workload analysis when operating the RNP system in association with other piloting requirements should be conducted by the applicant during all phases of flight and found to be acceptable, including those non-normal procedures that can be evaluated in flight.

(f)      Where the RNP System is capable of automatically intercepting a vertical path, the vertical fly-by and the autopilot response (if applicable) should be evaluated under different configurations and winds.

(g)      If the equipment uses barometric input, the applicant should verify that the equipment properly interprets the barometer reading. Special consideration should be given to manually entering barometric corrections.

(h)     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.

(i)      Data should be gathered using a variety of descent rates, angles, and lateral navigation source inputs available to the BARO-VNAV system.

Note: GNSS SBAS LNAV/VNAV most closely emulates BARO-VNAV performance.

(j)      When a Class A TAWS is installed and LPV minima are foreseen to be used, the applicant should verify the interface between the TAWS and the RNP system by checking the excessive downward deviation from the glide path.

(k)      When temperature compensation is enabled, the applicant should ensure that the display of corrected altitude(s) is consistent on all displays in the cockpit.

(l)      Where the RNP system provides both Barometric VNAV and SBAS/GNSS VNAV, the applicant should ensure that transitions from one source to the other do not result in transients or jumps that would cause either a sudden change in aircraft position on the flight path or in commands that could contribute to destabilisation of the aircraft.

(8)     Supplementary testing for applications for advanced RNP

(a)      The applicant should evaluate the aircraft response to the insertion of a hold to a manual termination. This evaluation should be performed at different altitudes, under different wind conditions, and for different aircraft operating speeds.

(b)     RF legs should be evaluated as detailed in Appendix D.

(c)      The use of different navigation accuracies (RNP values) between 0.3 and 1 NM should be evaluated. The applicant should particularly evaluate the aircraft response to navigation accuracy changes and should check that:

(i)      the display update following the navigation accuracy change is appropriate;

(ii)     the display of the updated navigation accuracy is consistent with all displays in the cockpit; and

(iii)     the steering response while the flight director and/or autopilot are/is coupled to the RNP system during the navigation accuracy change is appropriate.