Air France acknowledged yesterday that speed monitors on some of its Airbus planes have proved faulty, icing up at high altitude, and that recommendations to change them were first made in September 2007. The airline's statement followed word from the French agency investigating the disaster of Flight 447 that the instruments were not replaced on that aircraft – an A330 – before it crashed last week into the Atlantic Ocean.
The news came as the first bodies of passengers – two males – were found yesterday in mid-ocean by Brazilian search teams. Debris from the downed plane is also believed to have been recovered. But of the black boxes, there is yet no sign.
Any doubts about just how huge a task it is trying to find the cause of the crash of Flight 447, were removed at the headquarters of BEA, the French accident investigation agency, yesterday morning. The agency's head, Paul-Louis Arslanian, took a pinger from a flight recorder, held it in the palm of his hand, and said: "This is what we are looking for in the middle of the Atlantic Ocean. You see the complexity of the problem."
And that's not all. The pinger – a beacon that emits a signal – may not, said Mr Arslanian, still be attached to the cockpit voice and data recorders – known as the "black boxes" even though they are housed in orange cases about the size of a large petrol can. And if that is the case, then the reason the Air France flight from Rio de Janeiro to Paris went down with all 228 people on board last Monday may never be known. After all, the area where it crashed has, in places, a sea bed fully 15,000ft from the surface. A French nuclear-powered submarine, the Emeraude, is on its way to the area to try to detect a signal. It will arrive this week.
The Air France A330-200 was four hours en route from Rio de Janeiro to Paris when it suffered a rapid succession of technical problems. French and Brazilian aircrews and ships are scouring a stretch of ocean of several hundred square miles, some 680 miles (1,100 kilometres) north-east of Brazil's coast. Visibility and weather conditions in the search area improved yesterday, and Brazilian air force spokesman Colonel Jorge Amaral said that 14 planes and three ships are now patrolling the area.
Aviation officials have said the crash investigation is increasingly focused on whether external instruments may have iced over, confusing speed sensors and possibly leading computers to set the plane's speed too fast or slow – a potentially deadly mistake in severe turbulence. An Air France statement said that icing of the monitors at high altitude has led at times to loss of necessary flying information.
However, the later Air France statement stressed the recommendation to change the monitor "allows the operator full freedom to totally, partially or not at all apply it". Air France said that only a "small number" of incidents linked to the monitors had been reported. Airbus has said BEA found the doomed flight received inconsistent airspeed readings by different instruments as it struggled with turbulence in a massive thunderstorm.
BEA said yesterday that Air France had not acted on a recommendation to change airspeed-detecting instruments on Flight 447. Airbus had recommended to all its customers that they replace speed-measuring instruments known as Pitot tubes on the A330, said BEA's Mr Arslanian. But Alain Bouillard, the head of the French investigation, said: "They hadn't yet been replaced," on the plane that crashed.
Air France said it began changing airspeed sensors on Airbus long-haul aircraft due to icing fears five weeks before the crash of Flight 447, but only after failing to agree a fix with Airbus. The airline said it began to notice airspeed problems from icing on both A330 and A340 planes in May 2008, and had requested a solution from the manufacturer. According to Air France, Airbus proposed testing different sensors, but the airline declined to wait and started changing them from 27April. Pitot tubes protrude from the wing or fuselage of a plane and help measure the speed and angle of the flight, along with less vital information such as the outside air temperature. They feed airspeed sensors and are heated to prevent icing.
A blocked or malfunctioning Pitot tube could cause an airspeed sensor to work incorrectly and cause the computer controlling the plane to accelerate or decelerate in a potentially dangerous fashion in rough weather. An Air France memo about the crash sent to its pilots on Friday said the airline is replacing Pitot tubes on all its medium- and long-haul Airbus jets.
Investigators are relying on 24 messages the plane sent automatically during the last minutes of the flight to try to locate the wreckage. The signals show the plane's autopilot was not on, officials said, but it was not clear if the autopilot had been switched off by the pilots or had stopped working because it had received conflicting airspeed readings.
But questions about speed sensors are just one of many factors investigators are considering. Automatic transmissions from the aircraft showed a chain of computer-system failures that indicate it broke apart in mid-air. Just how, and why, may never be known.
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