Appendix A – TAWS installations testing guidance material

ED Decision 2022/008/R

General Testing:

(a) Most of the testing of a TAWS installation can be achieved by ground testing that verifies system operation, interfaces between affected aeroplane systems, correct warning prioritisation, and freedom from unwanted interaction or interference.

(b) The use of the TAWS as an integrated part of the aeroplane flight deck should be demonstrated. The TAWS should be shown to be compatible with the operation of the installed navigation systems, the airborne collision and avoidance system (ACAS), the windshear warning system, and the weather radar.

(c) The tests should evaluate the effects of sensor failure on TAWS operation.

(d) Flight testing should be carried out to evaluate overall operation, compatibility of TAWS with warning systems, navigation systems, and displays, freedom from unwanted interference, and to assess, during adverse flight conditions, instrument visibility, display intelligibility, sound levels and intelligibility of voice announcements, and the effects of electrical transients.

(e) Adequate flight testing to evaluate the terrain display can be conducted while verifying all the other required TAWS functions. Emphasis could be placed on showing compliance with CS ACNS.E.TAWS requirements during normal aeroplane manoeuvres for all phases of flight. Pop-up and auto-ranging features could be evaluated if applicable. Sustained turns could be performed, to evaluate for example symbol stability, flicker, jitter, display update rate, readability, the use of colour to depict relative elevation data, caution and warning alerts, and overall suitability of the display.

GPWS Testing:

(a) Flight testing to verify the proper operation of Basic GPWS functions can be conducted in any area where the terrain elevation is known to the flight crew. The following information provides an example of guidance for conducting flight tests to verify the proper operation of each GPWS function.

(1) Excessive Rate of Descent. Descents toward near level terrain are recommended if they provide the best results and ease of correlation with designed Mode 1 envelopes. This test verifies the operation of barometric altitude (and the corresponding computation of barometric altitude rate) and radio altitude.

(2) Excessive Closure Rate To Terrain. It is recommended that one level test run at an altitude between 150 m (500 ft.) and 300 m (1000 ft.) above the terrain elevation be conducted. This test will verify the proper installation of the radio altimeter.

(3) Negative Climb Rate or Altitude Loss After take-off. If it is adequate this test can be conducted immediately after take-off before climbing above 700 AGL or above runway elevation. This test verifies the proper operation of barometric altitude, barometric altitude rate and radio altitude.

(4) Flight Into Terrain When Not In Landing Configuration. If it is adequate this test can be conducted while on a visual approach to a suitable runway. This test verifies the proper installation of barometric altitude, barometric altitude rate and radio altitude as well as the gear and flap sensor inputs to TAWS.

(5) Excessive Downward Deviation from a glide slope or glide path. These tests should be conducted, as applicable, during:

(i) an ILS approach to verify the proper operation of the ILS glide slope input to TAWS;

(ii) an RNP approach to LPV minima to verify the proper operation of the glide path input from the GNSS receiver or FMS to the TAWS;

(iii) a GBAS approach to verify the proper operation of the GBAS glide path input to TAWS.

(6) Voice Callout ‘Five Hundred ft. This test should be conducted during an approach to a suitable runway in order to verify the proper operation of barometric altitude and/or radio altitude.

(7) Go-around. This test can be performed to confirm that nuisance alerts do not occur during normal go-around manoeuvres.

FLTA Testing:

(a) Flight testing to verify the proper operation of the FLTA function can be conducted in an area where the terrain elevation for the test runs is known within approximately 90 m (300 ft.). Two test runs can be performed:

(1) In level flight at approximately 150 m (500 ft) above the terrain of interest.

(2) While descending toward the terrain of interest.

(b) In each test case, the terrain display, the aural and visual alerts, the navigation source input, and the terrain data base can each be evaluated if necessary. Confirmation that the specific terrain cells do generate the required alert can also be evaluated if necessary.

Note: To conduct the test as described, the chosen terrain could be for example at least 28 Km (15 NM) away from the nearest airport. If this is not practical, the fly-over altitude will have to be lowered, for example to 90 m (300 ft.) or less above the terrain in order to generate a TAWS alert.

PDA Testing:

(a) Flight testing to verify the proper operation of the PDA function can be conducted in any airport area within an adequate distance of the nearest runway for example, 18.5 Km (10 NM). The aeroplane should be configured for landing at an adequate height for example, 450 m (1500 ft.) AGL, along the final approach segment of the runway at an adequate distance from the runway, for example, 18.5 Km (10 NM).

(b) At a suitable point, a normal flight path angle descent, for example, three degrees can be initiated and maintained until the PDA alert occurs. This test may exercise also, if necessary the 500 ft. voice callout.

The adequacy of the PDA aural alert should be verified during this test. If necessary, this test could verify the adequacy of the airport data base, the navigation source input and the barometric and/or radio altitude inputs to TAWS.

Note: The area in the vicinity of the runway selected for this test should be relatively free from terrain and obstacles to preclude activation of the FLTA function. Approximately level terrain along the final approach segment will exercise the PDA function.

(c) Flight tests should be conducted to verify that conditions at 300 m (1000 ft) AGL within 18.5 – 28 Km (10 -15 NM) of the nearest airport the TAWS system does not generate alerts.

[Issue: CS-ACNS/2]

[Issue: CS-ACNS/4]

Appendix B – Example of an acceptable TAWS installation

ED Decision 2022/008/R

An example of an acceptable installation is a single approved TAWS comprising the following components or inputs:

(a) A single terrain awareness and warning computer.

(b) A single radio altimeter sensor.

(c) A single air data system.

(d) An ILS/GBAS/SBAS/MLS/MMR receiver for Class A TAWS only.

(e) An interface with the landing gear and flaps.

(f) A roll attitude sensor.

(g) An accurate source of aeroplane position e.g. Flight Management System (FMS), or a Global Positioning System (GPS) or both.

(h) Where operations are reliant on the use of QFE, an adequate means of determining the altitude should be provided.

(i) A terrain data base covering the expected region of normal operations, together with a means of updating the stored data and to check its validity (by effective date and geographical region)

(j) A terrain awareness display.

(k) A loudspeaker for voice announcements.

(l) Consideration should be given to presenting voice announcements via headsets at a preset level particularly where active noise-reducing or noise cancelling headsets are used.

(m) Indication of TAWS and sensor failures.

(n) Indication that the TAWS is operating in Basic GPWS mode only.

(o) A means to initiate the TAWS self-test function on the ground.

(p) An interface with the flight recording system to record TAWS alerts and inhibition of FLTA or PDA functions.

(q) Indication to the flight crew where geographical regions of operation or other factors which adversely affect system performance to the extent that the TAWS may be potentially misleading and should not be relied up. If this indication is not practicable, a flight crew procedure may be used to determine whether the navigation system accuracy is acceptable for continued use of the TAWS.

(r) A means for the flight crew to inhibit the FLTA and PDA functions together with appropriate annunciation of the inhibited condition.

(s) A display with a means for the flight crew to select or deselect the terrain information. An automatic pop-up mode may be used with a simple means to deselect the terrain information after an automatic pop-up.

[Issue: CS-ACNS/4]

Appendix C – Background information on terrain awareness and warning systems (TAWSs)

ED Decision 2022/008/R

(a) General

This Appendix provides additional references, background information, and guidance for maintenance testing, as appropriate to TAWS installations.

(b) Related references

(1)  EASA

(i) ETSO-C151b Terrain Awareness and Warning System (TAWS)

(ii) ETSO-C92c Ground Proximity Warning, Glide Slope Deviation Alerting Equipment dated 24/10/2003

(iii) ETSO-C10b Aircraft Altimeter, Pressure Actuated, Sensitive Type dated 24/10/2003

(iv) ETSO-2C87 Low Range Radio Altimeters dated 24/10/2003

(v) ETSO-C106 Air Data Computer dated 24/10/2003

(vi) ETSO-C115b Airborne Area Navigation Equipment using Multi-Sensor Inputs dated 24/10/2003

(vii) ETSO-C129a Airborne Supplemental Navigation Equipment Using Global Positioning System (GPS) dated 24/10/2003

(viii) ETSO-C145 Airborne Navigation Sensors Using the Global Positioning System (GPS) Augmented by the Wide Area Augmentation System (WAAS) dated 24/10/2003 – ETSO-C145c Airborne Navigation Sensors Using the Global Positioning System Augmented by the Satellite Based Augmentation System (SBAS) dated 21/12/2010

(ix) ETSO–C146 Stand-Alone Airborne Navigation Equipment Using the Global Positioning System (GPS) Augmented by the Wide Area Augmentation System (WAAS) dated 24/10/2003 – ETSO-C146c Stand-Alone Airborne Navigation Equipment Using the Global Positioning System Augmented by the Satellite Based Augmentation System (SBAS) dated 21/12/2010

(x) ETSO-C196a Airborne Supplemental navigation Sensors for Global Positioning System Equipment Using Aircraft-Based Augmentation dated 05/07/2012

(xi) ETSO-C105 Optional Display Equipment for Weather and Ground Mapping Radar Indicators dated 24/10/2003

(2) ICAO

Doc 8168 Aircraft Operations Procedures for Air Navigation Services Fifth edition – 2006 Volume II Construction of Visual and Instrument Flight Procedures

(3) EUROCAE

(i) ED-98 () User requirements for Terrain and Obstacle Data (any edition - last edition B dated September 2012)

(ii) ED-76 Standards for processing aeronautical data dated October 1998 (identical to RTCA DO-200A)

(4) RTCA

DO-161A Minimum Performance Standards-Airborne Ground Proximity Warning Equipment dated 27/05/1976

[Issue: CS-ACNS/4]