I, WILLIAM BRUCE BYRON, Director of Aviation Safety, on behalf of CASA, make this instrument under regulation 21A of the Civil Aviation Regulations 1988.
[Signed Bruce Byron]
Bruce Byron
Director of Aviation Safety and
Chief Executive Officer
19 December 2007
Civil Aviation Order 108.36 Instrument 2007
1 Name of instrument
This instrument is the Civil Aviation Order 108.36 Instrument 2007.
2 Commencement
This instrument commences on the day after it is registered.
3 New Civil Aviation Order 108.36
Civil Aviation Order 108.36 is repealed and a new Civil Aviation Order 108.36 substituted as set out in Schedule 1.
Schedule 1 Civil Aviation Order 108.36
Specification — airborne radio systems
1 Application
This Civil Aviation Order specifies a design standard for Ground Proximity Warning Systems (GPWS) issued under regulation 21A of the Civil Aviation Regulations 1988.
2 Equipment design requirements
2.1 The equipment must comply with:
(a) Technical Standard Order — C92b “Ground proximity warning — glide slope deviation alerting equipment” of the United States of America Federal Aviation Administration; or
(b) specification No. 14, issue 2, “Ground Proximity Warning Systems” of the United Kingdom Civil Aviation Authority.
2.2 All sensors used in the installation must meet the specifications of the GPWS manufacturer.
3 Installation
3.1 The installation must meet the equipment manufacturer’s recommendations and must be designed to meet the following requirements:
(a) false warning must not be caused by supply voltage transients or interruption to primary power; and
(b) performance of the GPWS and other systems existing in the aircraft must not be degraded by mutual interference.
Note A typical interference test schedule is given in Appendix I.
3.2 Emergency means to deactivate the warning indication on all modes may be provided. The circuit breaker for the GPWS computer will normally be acceptable for the purpose. If a separate switch is provided, it must be guarded.
3.3 Means to deactivate the glideslope alert indication, Mode 5, must be provided for flight crew use in planned, abnormal or emergency conditions. Where Mode 5 has been deactivated, it must be automatically reactivated for the next approach or there must be a crew procedure to ensure it is reactivated when appropriate.
Note Acceptance of the crew procedure will require provision of an indicator or to alert the crew that deactivation action has been taken. A light will be acceptable.
3.4 A test facility must be provided which will allow the crew to determine serviceability of the system before take-off.
3.5 A separate control may be provided to inhibit Mode 4 warnings based on flaps being in other than the landing configuration. Where this provision is made, the control must be a guarded switch.
3.6 The aural warning must be fed to a non-mutable speaker located so that its output may be heard by both pilots. The level of the aural warning must be acceptable to the Director and must be so adjusted that it may be heard above the greatest ambient noise condition normally encountered in flight but must not be such as to interrupt communication between crew members. Once the level has been determined, no provision will be made for its variation by flight crew or maintenance personnel.
Note Appendix III contains acceptable means of assessing this level.
3.7 Where the aural warning is fed to a headset, no switching selection will be necessary for its reception. The level of the warning must not be affected by operation of any other audio selector switch and must not be such as to interfere with crew intercommunication or reception from ground stations.
Note It is recommended that the headset warning be provided in addition to the warning provided to the speaker.
3.8 The visual warning for Modes 1 through 4 must be in the field of view of both pilots and must be distinctive under all normal lighting conditions and commensurate with other cockpit warnings. The colour of the warning must be on a red background or comprise red letters. The letters must be “PULL UP”, “TERRAIN”, “GPWS” or other legend acceptable to the Director.
3.9 The radio altimeter used as a sensor for the system must have a height indicator on the flight crew instrument panel.
4 Flight testing
4.1 Unless the Director otherwise agrees, a flight test program must be performed on the initial installation of a particular model GPWS in each aircraft type.
Note 1 Adequate evidence showing that the particular model GPWS is acceptable to the airworthiness authority of the country of manufacture of the aircraft must normally be acceptable evidence to waive this requirement.
Note 2 Appendix III gives information on the circumstances under which this requirement may be varied and detail of typical tests required.
4.2 Where no performance data acceptable to the Director has been supplied for the radio altimeter used in the GPWS, the radio altimeter must be flight tested to show that it performs its intended function.
Note An acceptable test schedule is given in Appendix II.
5 Documentation
5.1 The aeroplane flight manual must include a statement listing the specific input sources necessary for GPWS activation. Procedures for operation, test, inhibition and a statement of the effect of aeroplane configuration on the system should also be given.
5.2 The maintenance manual for the aeroplane must contain sufficient material for the maintenance of the system.
5.3 For each installation, evidence must be provided to show that the performance of the system in flight complies with this specification.
Note Appendix III gives guidance on flight test requirements.
5.4 Where applicable, evidence must be provided to show that the radio altimeter used in conjunction with the GPWS performs its intended function.
Appendix I
Typical interference test
The following is listed as guidance for the type of testing necessary to check for interference between the GPWS and existing systems. The tests should be conducted outside the hangar in an interference free area.
1 Turn off all radios, electronic systems and motors so that individual systems can be switched on in turn.
2 After each system has been switched on in turn, the GPWS should be switched on. There should be no change in visual indications or audio output of the system under test or the GPWS. Repeat the check by switching to GPWS test.
3 Carefully monitor the GPWS during engine start and subsequent electrical power switching; there should be no visual or aural warning during the starting procedure.
Appendix II
Radio altimeter flight testing
1 When the radio altimeter used for the GPWS has been previously fitted and data exists to show that it performs its intended function, no additional testing is necessary to demonstrate altimeter performance.
2 Where the radio altimeter has not previously been shown to perform its intended function, flight testing will be necessary. Since the radio altimeter is required to be an approved type, the major performance parameters will have been established. The flight tests should, therefore, be directed towards those installation factors which affect performance and should include:
(a) tests specified by the manufacturer; and
(b) a coarse accuracy check against a barometric altimeter (at say 2 000 feet AGL) to identify any gross error; and
(c) an examination of the antenna radiation pattern. This would involve rolling and pitching the aircraft to determine adequate beam coverage and to identify spurious effects. Suggested manoeuvres are roll 20o and pitch up 15o; and
(d) such tests as would identify any unacceptable sidelobes of the antenna. These tests should involve lowering of flaps, landing gear, etc to see whether any unacceptable false altitudes are indicated or any other spurious effect results; and
(e) an assessment of radio altimeter aural and visual warnings to determine their adequacy in the flight environment; and
(f) a descent and approach to verify acceptable operation for the indicated height range of the system. Tests on a theodolite range are preferred but, if this facility is not available, the following test will suffice. During the ILS approach check, the indicated radio height at the outer marker and on touch down verify that the indicated radio height reads zero; and
(g) such interference and bus switching tests as would identify whether spurious indicated height or flag operation occurs.
Appendix III
Acceptable ground and flight tests to demonstrate ground proximity warning system performance
1 The Director will accept evidence from ground testing, where appropriate, and also flight test evidence from other aeroplane types which may be applicable to the aeroplane under consideration. The following gives guidance on flight test requirements:
(a) for aeroplanes of the same type and model fitted with the same system (GPWS computer and associated sensors), a flight test will be normally required only on the initial installation;
(b) the same evidence may be accepted for other aeroplanes of the same type, but a different model fitted with the same system, where it can be shown that the model difference cannot affect the performance of the GPWS;
(c) in other cases, a flight test of the system will normally be required.
2 The typical flight tests which follow are for guidance purposes and are based on the envelopes of Appendix A to Radio Technical Commission for Aeronautics Document D0161A.
Where a specific manufacturer’s equipment approved to the FAA TSO-C92b, or the CAA specification No. 14, issue 2, differs from those envelopes, the manufacturer’s data should be used for developing equivalent tests.
3 Before any test is conducted on the GPWS, the performance of the radio altimeter system must have been shown to be satisfactory. Appendix II covers radio altimeter testing.
4 Verify by ground tests specified by equipment manufacturer that the system is performing correctly.
5 Before flight, operate the GPWS self-test and determine the system is functioning correctly.
6 The audio warning level should be assessed under conditions of:
(a) high aerodynamic noise with a radio noise background and the ears covered by the headset used in that aircraft type; and
(b) VMO high speed warning with the ears covered by the headset used in that aircraft type; and
(c) approach speed with 1 ear uncovered and the other ear covered by the headset used in that aircraft type.
A “T” pad may be installed in the GPWS speaker circuit to obtain a suitable level. After determination of an acceptable level, the total attenuation should be noted so that a fixed value attenuator can be permanently fitted in the installation.
7 Mode 3 — descent after take-off – test
This test must be initiated below 700 feet radio altitude.
(a) Mode 3A — descent rate after take-off – test
Climb to 600 feet AGL then start a shallow descent.
At approximately 500 fpm descent rate, and with the naps not in the landing configuration, there should be a GPWS warning.
(b) Mode 3B — altitude loss after take-off – test
Climb to 600 feet AGL, observe the barometric altitude.
Start a shallow descent (approximately 300 fpm). With an altitude loss of approximately 60 feet, there should be a GPWS warning.
After either of the above tests, place flaps to the landing configuration and climb to 600 feet AGL radio atititude. Do not exceed 660 feet radio altitude. Commence a descent of approximately 400 fpm and continue down to 300 feet radio altitude. There should be no GPWS warning.
8 Mode 1 — excessive rate of descent with respect to terrain – test
Climb to 4 000 feet AGL with flap and gear positioned according to normal flight procedures.
At 4 000 feet, start a descent of 4 000 fpm. The GPWS warning should come on between:
2 300 feet and 1 700 feet AGL for envelope 1;
2 200 feet and 1 600 feet AGL for envelope 2;
1 700 feet and 1 000 feet AGL for envelope 3.
Reduce the descent rate and stabilize at approximately 2 000 fpm. The warning should cease.
Descent at 2 000 fpm. The GPWS warning should come on again between:
900 feet and 600 feet AGL for envelope 1;
600 feet and 300 feet AGL for envelope 2;
500 feet and 300 feet AGL for envelope 3.
Start climbing and the warning should cease.
9 Mode 2 — excessive closure to terrain – test
This test is meaningful only if it is performed with a known terrain slope such that by using ground speed, the terrain closure rate can be calculated.
For the test, 4 000 fpm is an optimum rate.
Note Figure 1 illustrates 1 set of conditions where this closure rate could be achieved.
Flight path 150 knots ground speed
Figure 1
Position the gear up and flaps not-in-landing configuration. Commence the flight towards the test terrain at a radio altitude stabilized at approximately 2 500 feet AGL, maintain barometric altitude and 150 knots ground speed. For the conditions of Figure 1, the warning should come on between 1 700 feet and 1 200 feet AGL.
Circle the area and prepare for another flight towards terrain with gear down and flaps not-in-landing configuration.
Commence the flight toward test terrain as before. The warning should come on between 1 000 and 650 feet AGL.
10 Mode 4 — flight into terrain with less than 500 feet terrain clearance and not in landing configuration – test
(a) Envelope 1
Do not exceed 600 fpm sink rate as a flap warning will occur when gear only is being tested.
Initiate approach to runway at a descent rate of 600 fpm with gear up and flaps not-in-landing configuration.
The GPWS warning should come on between 550 and 450 feet AGL. Lower the gear and warning should cease.
Continue the approach without exceeding 600 fpm descent rate. The GPWS warning should come on between 220 and 180 feet. Position the flaps to the landing configuration and the warning should cease.
(b) Envelope 2
Repeat the procedure for envelope 1 but at a descent rate of 1 300 fpm. The relative warnings for gear and flaps should be 550-450 feet and 170-130 feet AGL.
(c) Envelope 3
Repeat the procedure for envelope 1. The relative warnings for gear and flaps should be 500-400 feet and 130-50 feet AGL.
11 Mode 5 — below glideslope – test
Initiate an ILS approach.
With the gear in the landing configuration establish a 1.3 dot (97.5 microamps) fly up configuration.
The glideslope warning should come on at approximately 1 000 feet AGL and with a soft voice.
Establish an approximately 2 dot (150 microamps) fly up configuration. The glideslope warning should come on with a loud voice.
