Air France to replace speed sensors in wake of AF 447 crash

Air France has agreed to replace the air speed monitors on its fleet of Airbus A330 and A340 aircraft “within a few days,” the company’s majority union said. The announcement comes amid growing speculation that conflicting information from the monitors, known as Pitot probes, could have caused last week's deadly Atlantic crash.

As debris from the AF447 jet and victim’s bodies are painstakingly recovered from the Atlantic Ocean, converging elements seem to point towards a possible link between faulty speed sensors and the sudden and mysterious disappearance of the Rio-Paris flight. The bodies of the first 16 victims found have been transferred to the Brazilian island of Fernando de Norona where they will undergo DNA identification tests.

Incoherent speed data

The French aviation investigation and analysis bureau (BEA) stated on Saturday that the doomed jet broadcast a series of 24 automatic error messages in the final minutes of its flight, which seem to indicate that the cockpit was receiving “incoherent” speed data.

Reacting to this statement, France’s Transport Secretary, Dominique Bussereau, stressed on French radio RTL on Sunday that “its still to early to focus on any single hypothesis”, but explained how a malfunction of the Pitot tubes could lead to an accident as tragic as the AF447 flight’s. “When these probes freeze due to a sudden drop in temperature in a very humid zone, a turbulence zone, they no longer indicate the correct speed”, he said. The result being that “pilots no longer read the correct speed in the cockpit” and may enter a stormy cloud too slowly.

Air France announced on Saturday that it had already begun replacing speed monitors on its planes since April 27 as part of standard modernisation procedures, “without presuming a link” between the Pitot probes and the crash. According to an internal memo obtained by French news agency AFP, Air France had warned its pilots as early as November 2008 about "a significant number of incidents" linked to the Pitot probes.

According to French weekly Le Journal du Dimanche, incidents on A330 aircraft linked to faulty speed sensors had been identified as early as 1996. An Air France technical memo written at the time indicated that the Pitot probes could emit faulty speed measures “even if their anti-freeze system had functioned normally”, in particular when crossing an area of “stormy clouds in an inter-tropical convergence zone”. These appear to be precisely the meteorological conditions the plane faced before it crashed.

One of Air France’s minority unions, Alter, has advised pilots to refuse to fly all A330/A340 aircraft until the replacements have been completed. It deplored that the company did not decide to halt flights on these planes while the suspected probes were still in use.  

No single crash factor

Interviewed by FRANCE 24, Aviation Weekly expert Pierre Sparaco explained that at this point “we can only guess as to whether speed sensors played a possibly critical role in the flight’s crash”, stressing that A330 aircraft have been in service with the same type of probe for 15 years in over 60 different airline companies. “Why a malfunction would emerge now after remaining hidden for 15 years is a question I cannot answer,” he said.  Airline experts, he explained, agree to say that “no accident is the result of one single reason but of several factors. It’s what we call in investigator slang a catastrophic sequence of events”. Investigators can only hope that the the voice and data recorders located in the tail of the plane will unveil more about the deadly sequence.

Although some experts have linked the AF447 crash to severe losses of altitude by two Qantas jets which also used Pitot probes, the Australian carrier has denied any link between the incidents, confirming that it uses a different speed sensor manufacturer than that of Air France.

Air France flight 447 disappeared over the Atlantic on June 1 with 228 people on board while en route to Paris from Brazil, making it the deadliest aviation accident since 2001 and the worst in the company's history.