COMMONWEALTH OF AUSTRALIA (Civil Aviation Regulations 1998), PART 39 - 107 CIVIL AVIATION SAFETY AUTHORITY
SCHEDULE OF AIRWORTHINESS DIRECTIVES
Radio Communication and Navigation Equipment
AD/RAD/66 Mode S Altitude 12/99 DM
Applicability: All aeroplanes equipped with one or more Mode S transponder systems connected to a TCAS II.
Requirement: 1. Determine the source(s) of pressure altitude data to the Mode S transponder(s) by inspection and reference to the build standard of the aircraft, together with the Maintenance Manual and Wiring Diagram Manual.
2. Following the determination at Requirement 1, action as follows:
- For aircraft using altitude data input to the Mode S transponder(s) and encoded in other than Gilham format (eg databus or synchro formats), no further action is necessary.
b. For aircraft where altitude data is encoded in Gilham format and inputs to each Mode S transponder are provided from dual altitude encoders:
(i) For each transponder confirm, by inspection and reference to both aircraft and equipment Maintenance Manuals and Wiring Diagram Manuals, that the transponder altitude comparator function is enabled, and, using appropriate test equipment, demonstrate that the comparator detects altitude data differences between the dual encoders of more than 600 feet.
(ii) Amend the approved System of Maintenance to provide a verification test of the functionality of the transponder altitude data comparator at periods not to exceed 24 calendar months.
c. For aircraft where altitude data in Gilham format is provided to each Mode S transponder from a single altitude source:
(i) Test the systems using appropriate test equipment to verify that the altitude readout of the Mode S is correct throughout the operating envelope of the aircraft.
3. If, as a result of the Requirement 2.b.(i) inspection/test, the altitude comparator function is found not to be enabled or is unserviceable, enable and/or rectify the comparator.
Note 1: CAA(UK) AD 001-08-99 refers.
Compliance: 1. Within 45 days from the effective date of this Directive.
2. b. (i) Within 45 days from the effective date of this Directive.
COMMONWEALTH OF AUSTRALIA (Civil Aviation Regulations 1998), PART 39 - 107 CIVIL AVIATION SAFETY AUTHORITY
SCHEDULE OF AIRWORTHINESS DIRECTIVES
2. b. (ii) Within 90 days from the effective date of this Directive.
2. c. (i) Within 45 days from the effective date of this Directive and thereafter at intervals not to exceed 45 days until the aircraft is modified with either a single monitored air data sensor or dual independent altitude encoders and an altitude data comparator.
Note 2: The modification of the aircraft is an optional terminating action only, modification is not required by this Directive.
3. Before further flight.
This Airworthiness Directive becomes effective on 13 October 1999.
Background: The CAA(UK) and the Bureau of Air Safety Investigation have reported incidents where a potentially hazardous loss of separation occurred. One incident resulted from faults in the Mode S system in one of the aircraft were erroneous altitude data was being transferred to the TCAS II equipment. This transfer of the erroneous data resulted from a dormant fault in an altitude data source comparator, installed in the Mode S transponder.
This Directive requires confirmation that the altitude comparator is enabled or, where there is only single altitude data source, the repetitive checking of the Mode S altitude readout.