United Arab Emirates (UAE) investigators have detailed how a UPS Boeing 747-400 freighter crew struggled with the oxygen supply and battled against a loss of flight control following the outbreak of fire, before the jet crashed in Dubai.
The latest interim inquiry report into the 3 September 2010 crash showed that the crew experienced decreased manual elevator and rudder control, consistent with a loss of column and pedal cable tension, while attempting to return to the UAE hub.
There was "nil to marginal" elevator deflection in response to large control column inputs, the General Civil Aviation Authority (GCAA) stated.
But it also highlighted the apparent difficulties the crew experienced with using breathing apparatus as the cockpit was filled with smoke.
As the 747 reached a cabin altitude of 21,000ft (6,400m) while carrying out an emergency descent, the captain made "several comments concerning the supply of oxygen into the mask", said the GCAA.
While both pilots had donned their oxygen masks after an initial fire warning sounded, the captain indicated - about 5min later - that oxygen was not being supplied to the mask. He asked the first officer to "get me oxygen" but the first officer responded that he did not know where to find it, at which point the captain handed him control of the aircraft and left his seat.
Cockpit-voice recorder analysis indicated that both pilots had "some unidentified issues with the crew oxygen system", said the GCAA. About 2min after the captain left his position, the first officer said, during a radio transmission: "I'm looking for some oxygen."
While his breathing was audible until the end of the cockpit recording, the first officer transmitted, about 10min before the crash, that he was "running out of oxygen". The aircraft, having missed its emergency approach to Dubai, attempted to divert to Sharjah but entered a descending turn and crashed.
The US National Transportation Safety Board has already issued new guidelines on the proper donning and use of selector switches on oxygen masks following the accident, in which both pilots were killed.
Investigators believe the source of the fire to have been on the forward main deck, below and behind the cockpit, and are examining the potential effect on the oxygen supply system from a fire in this vicinity.