A black box recovered, together with its cockpit voice recorder (CVR), damaged but usable ; that, in essence, is the information with which we came away from the press conference organized by the French Bureau of Enquiry and Analysis for Civil Aviation Safety (BEA), on 25th March. An audio data file has been recuperated from the Germanwings A320’s black box and is usable, according to the BEA, who have not yet had time to carry out their analysis.
Concerning the facts known to date, the last radio contact with the pilots did take place at 10:30 a.m. on the tragic morning. One minute later, the plane began a steady descent of about 1,000 metres (3,300 ft.) per minute, which continued until its impact with the ground at 10:40 a.m., as if the pilots were no longer in control.
BEA is currently offering no explanation for this continuous descent of the aircraft, nor on the loss of radio contact.
These facts, however, are reminiscent of another accident in 2005, that of the Helios Airways’ Boeing 737, causing 121 deaths, due to a slow depressurization of the cabin. On the day of the crash, mechanics had performed an on the ground pressurization test, at the end of which, they failed to reset the pressurization lever to ‘‘ automatic’’.
During its ascent, therefore, the cabin of the aircraft was not pressurized, leading to lack of oxygen. Pilots and passengers simply passed out, and the aircraft finally crashed after running out of fuel.
To find out how long it takes for an aircraft cabin to run out of oxygen, we went to the aeronautical suppliers, Liebherr Aerospace, who specialize in aircraft air handling systems.
Nicolas Bonleux, Managing Director, Liebherr-Aerospace & Transportation :
"It depends a lot on the flight phases, for instance the aircraft’s altitude. Then, it depends on the reason for the depressurization, and whether it's due to a small or large opening in the fuselage. So there’s no single categoric answer to the question. On the other hand, one thing is certain, is that if an aircraft is in a situation of depressurization, it must quickly reduce altitude, to where the atmospheric pressure outside is breathable for the passengers, i.e. around 3,000 metres (10,000 ft.)."
One reason, perhaps, why the Germanwings A320 pilots decided to descend, but why then, did they not use their oxygen masks in order to remain conscious ? Depressurization is just one hypothesis amongst others, so we will have to wait for the investigators’ analysis of the cockpit voice recorder data, and hope they find the other black box, containing the flight data recorder, to uncover the whole flight 4U 9525 story.