CYPRUS: The pilots of Helios flight 522 might have had as little as three seconds to pull on their oxygen masks to prevent unconsciousness after a sudden depressurisation of the aircraft.
Problems with the oxygen supply to the cockpit could have been a contributing factor to the crash, according to anonymous postings from pilots on the website for the Professional Pilots' Rumour Network (www.pprune.com) yesterday.
Many raised concerns that the oxygen masks in the Helios airline's Boeing 737-200 were either difficult for the pilots to reach or that the oxygen supply might have been turned off.
"The two masks for jumpseat riders on 737 are a bit hard to reach for either first officer or captain," said one posting. "[He] would have to bend his arm backwards and have a pretty fair reach."
Any delay in putting on the oxygen masks could have been fatal. "The reason you have to do it quickly is that, at high altitudes, the time of useful consciousness at best will be 15-20 seconds," says Capt Mervyn Granshaw, chairman of the British Airline Pilots' Association and a veteran pilot of commercial airliners including the Boeing 737-200.
"At worst it's three to five seconds - you can't hold your breath, it just comes out of you and then you fall over." The effects of a rapid depressurisation at cruising altitude, which can be up to 11,000 metres above sea level for a commercial airliner, are shocking.
The temperature inside the aircraft will drop to minus 50 degrees and the air pressure drop quickly brings unconsciousness.
"There are usually four separate ways of pressurising airplanes and it's a bad day if they all fail," said Capt Granshaw.
"It's an extremely bad day if they all fail and it's catastrophic as opposed to a slow leak."
In the main cabin, passengers are provided oxygen through a central reserve fed by chemical generators which normally last around 15 minutes. The assumption is that, after depressurisation, the plane will quickly be brought down to an altitude where masks will not be needed.
In the cockpit, the pilots' masks are fed from a dedicated bottle of gas. A posting on the pprune website considered the possibility the pilots' masks simply did not provide useable oxygen. "It is possible that the flight deck oxygen valve (located behind the first officer seat), and which supplies the pilots' oxygen masks, was turned to the off position and it is something that is not immediately obvious," said one pilot.
The sudden risks of depressurisation are well-known by commercial airline pilots and the oxygen supplies to the cockpit are normally checked before every flight. -(Guardian service)
Reuters adds: Cypriot police yesterday raided the Nicosia offices of Helios Airways, owners of the Boeing 737, a government spokesman said.
"After allegations brought by the Communications and Works Minister and the chief of police, the attorney general issued search warrants for the central offices of Helios to collect documents and other evidence that might be useful in a possible criminal investigation," spokesman Marios Karoyan said.