CYPRUS: Airline experts were at a loss to explain how a Cypriot aircraft carrying 121 people could have crashed yesterday after apparently losing cabin pressure or oxygen but said it was likely to be due to a combination of factors.
All experts spoken to by Reuters said it was extremely rare for a plane to lose oxygen as there was a set of emergency systems in place which should have kicked in.
They also could not understand why the pilots had not used additional oxygen supplies.
"The pilots should have had their masks on," a retired British pilot who did not wish to be named said.
"Why they didn't put them on is the big mystery."
The Cypriot airliner crashed into a mountainous area north of Athens, killing all 121 on board.
A Greek defence ministry official said the aircraft's oxygen supply or pressurisation system may have malfunctioned.
"A loss of pressurisation in the cabin is in itself a rare event but to go as far as it incapacitates the pilot is hugely rare," the retired pilot said.
Two Greek F-16 fighter jets were scrambled after the plane lost contact with the tower at Athens International Airport.
One of the jet pilots said he could not see the captain in the cockpit and his co-pilot appeared to be slumped in his seat.
A spokesman for the European Aviation Safety Agency, Daniel Holtgen, based in Cologne, Germany, said the cause of the crash was likely to be a combination of factors.
"It is highly unlikely that the loss of cabin pressure alone would cause such an incident. There would have to be other contributing factors."
The retired pilot said the cause was likely to be either a catastrophic or subtle depressurisation followed by a problem with the altitude warning system.
Greek TV station Alpha said the pilot told air traffic controllers that the Helios Airways Boeing 737 was experiencing air-conditioning problems before communication with the plane - flying at 35,000 feet en route from Larnaca in Cyprus to Prague via Athens - was lost.
Another media report said one passenger had sent a text message shortly before the crash saying it was freezing.
"When he talks about being extremely cold, that really suggests that there was possibly no air circulating in the cabin at all," Kieran Daly, editor of Air Transport Intelligence, told Reuters.
"It is quite a puzzle really, there are very good procedures in place for dealing with a lack of oxygen.
"It is extraordinary for this to happen on a fairly large airliner," he added.
Experts said they could only speculate as the investigation was still in the early stages, but the head of the accident investigation committee said the two black boxes - voice and data recorders - had been located.
"You tend to get very confused signals to start off with.
"However, they've got both recorders so there will be an answer," the retired pilot said.
"They will get to the bottom of this."