The Boeing 767 had just reached cruise altitude at flight level 330 approximately 40 minutes out of Singapore enroute to Perth, when the flight crew noted smoke and electrical fumes on the flight deck. The source of the smoke and fumes could not be readily identified. The pilot in command elected to have the flight crew don oxygen masks, and diverted to Jakarta.
The operator's engineering personnel examined the aircraft and found the right DME (Distance Measuring Equipment) circuit breaker open. Technicians isolated the problem to the right DME interrogator unit. The malfunctioning DME unit was disabled in accordance with the MEL (Minimum Equipment List) guidelines to allow the aircraft to continue to Perth. Following arrival in Perth, the unit was replaced.
Examination of the unit by the manufacturer revealed that the DME unit's A5 modulator had overheated. This failure mode was similar to two other units, which had overheated on a different aircraft in January 2000 (see Occurrence 200000055). The failure mode of those units was such that the A5 modulator had overloaded the positive 86 volt DC power supply and overheated the power transformer. Compliance with service bulletins recommending product improvements to this unit were not mandatory, and the recommended modifications had not been incorporated into this unit, or the previous two units that had sustained failures.
As a result of the investigation into this occurrence, the Australian Transport Safety Bureau has simultaneously issued Safety Advisory Notices 20000278 and 20000279 to the Civil Aviation Safety Authority and the Federal Aviation Administration respectively. These advisories suggested the Civil Aviation Safety Authority and the Federal Aviation Administration take appropriate action to mandate compliance with Service Bulletins DME 700-34-10, 17, 23, 34, and 35.
Any responses received to these Safety Advisory Notices will be published on the ATSB website at the conclusion of the investigation.
|Date:||06 September 2000||Investigation status:||Completed|
|Time:||0430 hours UTC|
|Location:||489 km ESE Singapore Jatcc, Aero.|
|Release date:||03 April 2001||Occurrence category:||Incident|
|Report status:||Final||Highest injury level:||None|
|Aircraft manufacturer||The Boeing Company|
|Type of operation||Air Transport High Capacity|
|Damage to aircraft||Nil|
|Departure time||1450 hours UTC|