AD/RAD/47 Amdt 4 - Periodic Testing of ATC Transponders (Cth)

AIRWORTHINESS DIRECTIVE

On the effective date specified below, and for the reasons set out in the background section, the CASA delegate whose signature appears below repeals Airworthiness Directive (AD) AD/RAD/47 Amdt 3 and issues the following AD under subregulation 39.001 (1) of CASR 1998 and subsection 33 (3) of the Acts Interpretation Act 1901. The AD requires that the action set out in the requirement section (being action that the delegate considers necessary to correct an unsafe condition) be taken in relation to the aircraft or aeronautical product mentioned in the applicability section: (a) in the circumstances mentioned in the requirement section; and (b) in accordance with the instructions set out in the requirement section; and (c) at the time mentioned in the compliance section.

Radio Communication (including Emergency Transmitters and Navigation Equipment)

AD/RAD/47 Amdt 4 Periodic Testing of ATC Transponders 7/2016

Applicability:

All Air Traffic Control transponders fitted to aircraft to which Part 42 of CASR 1998 applies.

Requirement:

1.    For all transponders, perform a system test in accordance with the requirements of United States of America 14 CFR (Federal Aviation Regulations) Part 43, Appendix F.

2.    For transponders utilising electron tube technology (ETT) perform the following tests to confirm:

a.     the duration of all reply pulses (pulse width) is between 0.35 to 0.55 microseconds; and

b.    the amplitude variation between one reply pulse and any other reply pulse is not greater than 1 dB.

For Requirements 1 and 2: Mode A code 2100 is to be used when carrying out transponder tests.

For Requirement 2 only: ETT means the technology that utilises physical and electrical characteristics of a physical body to oscillate and amplify a signal at its resonant frequency for subsequent broadcast.  This includes thermionic valves, klystrons or cavity oscillators etc.  As these components age, the characteristics which provide the signal stability vary, which affects the output signal.  Transponders utilising ETT include, but are not limited to, Honeywell (Bendix-King) KT76A, Narco AT150 and ARC RT859.

3.    Repair or replace any transponder that fails any of the Requirement 1 or 2 tests.

Compliance:

For Requirements 1 and 2: Within 24 calendar months after the effective date of this AD or within 24 calendar months after a system test was last accomplished in accordance with AD/RAD/47 Amdt 2, whichever occurs first, and thereafter at either:

a.     intervals not exceeding 24 calendar months; or

b.    intervals in accordance with an approved maintenance program for the aircraft under regulation 42.140 of CASR 1998.

Note:  Generic guidance on the testing of transponders is available in AWB 34-013 and AWB 34-09.

For Requirement 3: Before further flight after the Requirement 1 or 2 tests.

This AD commences on 23 March 2016.

Background:

AD/RAD/47 was originally issued to introduce a procedure additional to the transponder self-check prescribed in paragraph (4) (k) of section 5 of Schedule 5 of the Civil Aviation Regulations 1988 (CAR 1988), and to align with the requirements of overseas civil aviation authorities.

Amendment 1 advised of a new code, compatible with air traffic control requirements, that was to be used when testing transponder systems.

Following the deployment of new Mode S radar interrogators in Australia, it was discovered that variation in the height of reply pulses transmitted by the transponder could be misinterpreted by the interrogator and this may cause the Mode A code to appear to spontaneously change during flight. This may generate short term conflict alerts to be displayed to air traffic controllers.

Amendment 2 introduced serviceability checks to confirm that transponders utilising ETT are performing to the specifications to which they were originally certified.

Amendment 3 was issued to limit the applicability of the AD to Part 42 aircraft only.

Amendment 4 is issued to update a regulatory reference in the compliance section from regulation 42M of CAR 1988 to regulation 42.140 of CASR 1998. This AD will be repealed after the requirements are incorporated into a future amendment of the Part 42 Manual of Standards.

William M. David
Delegate of the Civil Aviation Safety Authority

18 March 2016