Report: Qantas B743 near Sydney on Feb 25th 2008, electrical smell in cockpit

[Guest Chainsaw]

Source: http://avherald.com/h?article=41a59ae7&opt=2048

 

A Qantas Boeing 747-300, registration VH-EBY performing flight QF-566 from Perth,WA to Sydney,NS (Australia) with 374 passengers, was enroute at FL370 about 150nm westsouthwest of Sydney, when the flight crew detected a smell that slowly increased in intensity. The crew donned their oxygen masks as they could not identify the nature of the smell. The crew executed the flight deck smoke/fumes evacuation and landing preparation checklists and confirmed, that all aircraft systems were working correctly. Cabin crew reported no smoke or smell in the cabin. The copilot declared PAN indicating, that the crew expected a normal approach and landing, Sydney Airport invoked their emergency plans. About 5 minutes later the crew initiated the descent to Sydney, the captain announced the possibility of an emergency evacuation to the passengers. The aircraft touched down safely about 30 minutes after the onset of the smell, the flight crew requested an external inspection of the airplane immediately after vacating the runway and requested the fire trucks to follow the airplane to the gate, where the passengers disembarked normally.The Australian Transportation Safety Board (ATSB) released their final report stating, that maintenance could not find anything and could not reproduce the odour, so that the operator decided to carry out an assessment flight. While the aircraft taxied out for that flight, a faint smell became noticeable on the flight deck. With the help of a particle counter it was established, that the fume came from the lower left corner of the captain's windshield.

 

Subsequent examination revealed loose windshield heat element terminal connections causing electrical arcing resulting in fumes.

 

The left windshield and the heat element were replaced and a second assessment flight carried out without incident. The airplane was returned to service.

 

Due to previous similiar incidents Qantas as well as Boeing had developed engineering instructions in 2006 calling for recurring inspection of the connectors of the heat elements. The airframe had 751 hours to fly until the next recurring inspection was required by the Boeing engineering instruction. Boeing had also released a redesign of the windshield with a different electrical connection, that removed the requirement for the recurring inspection.

 

About 17 flight hours prior to the incident the airplane underwent maintenance at a contracted licensed facility during which the crash pad at the left hand windshield had been removed and refitted.

 

The ATSB concluded, that the loose terminal connections to the left windshield heat element increased the electrical resistance and resulted in electrical arcing and fumes on the flight deck. Another safety factor was the inadvertent disconnection of the captain's intercommunication system when the crew donned their oxygen masks. The potential of the recent maintenance work in the vicinity of the left windshield/crash pad/to have contributed to the insecurity of the left windshield terminal connections could not be determined. The redesign of the windshield by the manufacturer to improve the security of the windshield heater wiring connection should address the risk of electrical arcing in that component.

 

Windshield heat terminal block (Photo: ATSB):