Airline experts baffled by Cypriot plane crash

Airline experts were at a loss to explain how a Cypriot plane carrying 121 people could have crashed on Sunday after apparently losing cabin pressure or oxygen but said it was likely to be a combination of factors.

All experts spoken to 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 on Sunday, killing all 121 on board. A Greek Defence Ministry official said the plane'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 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 the plane 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, said.

"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."

All the experts spoken to 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."

Chronology - Recent major air crashes

A Cypriot airliner carrying at least 121 passengers and crew crashed north of Athens on Sunday, killing all aboard, Greek state television reported.

Here is a short chronology of some major air disasters in the last five years.

January 30, 2000: A Kenya Airways Airbus A-310 crashes in the sea shortly after take-off from Abidjan in the Ivory Coast, killing 169 of the 179 passengers and crew aboard.

April 19, 2000: An Air Philippines Boeing 737-200 crashes near the southern city of Davao killing all 131 on board. The crash was the worst in the Philippines' history.

July 25, 2000: An Air France Concorde supersonic airliner crashes just after taking off from Charles de Gaulle Airport, Paris, bound for New York. All 109 people on board are killed along with four on the ground. It was the airliner's first crash and caused all Concordes to be grounded.

August 23, 2000: A Gulf Air Airbus A-320 crashes in the waters off Bahrain on a flight from Cairo, killing all 143 aboard.

July 3, 2001: Nine crew members and 136 passengers are killed when a Russian Tupolev-154 plane crashed near the Siberian city of Irkutsk.

October 8, 2001: At least 114 people are killed when a Scandinavian Airlines System airliner and a small plane collided in heavy fog at Milan's Linate Airport.

November 12, 2001: An American Airlines Airbus A-300 bound for Santo Domingo, Dominican Republic, crashes into the New York borough of Queens minutes after take-off. At least 265 people were killed including five on the ground.

February 12, 2002: An Iran Air Tours TU-154 passenger plane flying from Tehran to Khorramabad crashes near the western city, all 119 people aboard died in the accident.

April 15, 2002: An Air China Boeing 767 passenger aircraft travelling from Beijing to Pusan in South Korea crashes into a mountain. Of the 166 on board, 38 survived.

May 4, 2002: A Nigerian EAS Airlines' BAC 1-11-500 with 105 people on board crashes in the northern Nigerian city of Kano. At least 148 people were killed.

May 7, 2002: A China Northern MD-82 jet falls into the sea off Dalian in northeast China, killing all 112 passengers and crew on board.

May 25, 2002: A China Airlines Boeing 747-200 with 225 people on board plummets into the sea while on a flight from Taiwan to Hong Kong.

February 19, 2003: An Iranian military plane crashes near Kerman in southeastern Iran. Iran said all 276 aboard were killed.

March 6, 2003: An Algerian flag carrier Boeing 737-200 crashes shortly after take-off from Tamanrasset airport killing 103 passengers and crew.

February 3, 2005: An Afghan airliner crashes into a mountain near Kabul, killing all 105 people on board. The Boeing 737 was operated by Afghanistan's only private airline, Kam Air.

August 14, 2005: A Helios Airlines Boeing 737 crashes in the area of Kalamos, 30 kilometres north of the Greek capital, Athens, killing all 121 passengers and crew on board.