THE Air France jet that crashed into the Atlantic with 228 people on board broke apart before it hit the water, throwing out some passengers at high altitude, investigators believe.

Their conclusion is based on the discovery of two trails of bodies more than 50 miles apart, suggesting that the Airbus split in two after going out of control in bad weather and turbulence during its flight from Rio de Janeiro to Paris on June 1.

Examination of bodies discovered off the northeastern Brazilian coast suggested that they were dead by the time they hit the water. They were stripped of clothes, apparently in the rush of air as they fell from as high as 35,000ft. Multiple fractures were most likely to have been caused by hitting the water at about 120mph.

The absence of any traces of an explosion, such as burn marks or inhaled smoke, supports the view of investigators that the disaster was caused by a combination of factors, possibly beginning with the blockage of speed sensors.

The sensors, called pitot tubes, are prone to getting clogged with ice and insects. One theory is that the “inconsistent” speed readings caused the automatic pilot to disengage, leaving the crew trying to fly manually – a difficult task at high altitude without knowing the plane’s speed.

It has emerged that the same sequence of events occurred in six cockpit emergencies reported by Airbus pilots over a year beginning in February 2008. According to internal Air France documents leaked to the press, the incidents involved “a rather incoherent cocktail of alarms” and “severe breakdowns”. These appear to have originated with malfunctioning pitot tubes in stormy weather.

In one incident, an Air France pilot issued a mayday call between Paris and Tokyo in turbulent weather after the loss of speed indication resulted in the disengagement of the automatic pilot and set off other alarms. In all six incidents, however, the pilots regained control of the aircraft.

Air France advised pilots on November 6 last year about the “significant number of incidents” in which false speed readings had confused the automated flight system.

The company rushed to replace speed sensors on its aircraft last week after a pilots’ union threatened to boycott long-range jets. Even so, questions were raised over why Air France had taken so long to act on advice from Airbus to upgrade pitot tubes in 2007. As early as 2001 an airworthiness directive from the US Federal Aviation Administration noted problems with pitot tubes on the Airbus A330 that could cause “inadvertent excursions outside the normal flight envelope”.

Pierre-Henri Gourgeon, Air France’s chief executive, last week acknowledged that malfunctioning speed sensors could have been “a contributing element” in the accident.

“We do not deny that there is a problem with the sensors,” he said. “But we cannot say that this is the cause of the accident. We do not know.” With no indication of how fast the plane is flying the pilot risks applying too much jet thrust or too little. At high altitude – in circumstances known as “coffin corner” – too much thrust will put a plane into a nosedive and too little will make it stall.

Among the sophisticated electronics on an Airbus A330 is a system that automatically pumps fuel aft when the plane climbs above 25,000ft. This alters the trim of the aircraft to improve fuel economy. It also alters the aircraft’s centre of gravity, making it harder to fly when in manual mode rather than autopilot.

Without the ability to read their speed, the crew of Flight 447 may have mistakenly believed there was a danger of stalling. If they applied extra thrust it could have tipped the plane out of control, tearing it apart in the turbulence.

The recovery of the “vertical stabiliser” from the tail of the aircraft has strengthened suspicions among experts that the plane went out of control and broke up as a result of flying either too slowly or too quickly in turbulence. Strong up or down draughts can exert extreme pressures on planes.

So far 50 bodies have been found out of the 228 passengers and crew aboard the aircraft. Passengers spanned 32 nationalities and included five Britons and three Irish women. Search teams say that after almost two weeks floating in waters rich in marine life the bodies are not in a state to be recognised by relatives and DNA testing is helping with identification.

Postmortem examinations on 16 of the bodies suggest they were dead when they hit the sea. No water was found in lungs, which would have indicated drowning. Passengers would have almost instantly fallen into a coma and died if there was a sudden depressurisation of the cabin at high altitude, say experts. Despite the length of time the bodies were in the water, it seems unlikely that wind or currents separated them into two distinct groups 50 miles apart.

The Emeraude, a French nuclear submarine, is combing the ocean depths in search of an audio beep from the plane’s “black boxes”. The flight data recorder and cockpit voice recorder ought to contain sufficient information to determine what caused the crash. However, officials are cautious about the chances of finding them in 12,000ft of water. No flight recorders have been retrieved from such a depth. A rugged, undersea terrain will not help.

“We are going to need a lot of luck,” said Patrick Prazuck, a military spokesman.

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