When did Air France know about faulty air-speed sensors?

An internal document shows the airline was aware of the problem more than a year before flight 447 disappeared.

The latest wrinkle in the AF447 mystery is not the black box. French authorities say recent sounds picked up in the cavernous depths of the Atlantic are “false signals.”

The hunt for the black box – and the cause of the June 1 crash – continues.

But another Air France internal document has surfaced, which reinforces the theory that the problem was the air-speed sensors known as Pitot tubes.

In a detailed June 23 post (in French and English) on the European pilots association website, Eurocockpit (and in a story in the weekly Le Canard Enchaine in Paris today), Air France document NT 34-029 suggests that the Pitot tubes were known to have been faulty far earlier than August 2008.

August was the date offered last week by Air France CEO Pierre-Henri Gourgeon as the earliest instance of Pitot tube failure.

The NT 34-029 document recounts seven cases of faulty Pitot tubes prior to August 2008. Given an Airbus investigation into the Pitot tubes, the malfunctions may date back as far as a year or more before then. The cited problems include an Airbus owned by Air Tahiti, serviced by Air France, and six other cases on the Airbus 340 model aircraft.

On June 19, Mr. Gourgeon, in an interview with French radio RTL, stated, “For the A330 and A340, we’ve had no incident prior to August, 2008.”

(Eurocockpit states separately that NT 34-029 was “filed” in June, but it is dated August, 2008.)

An Air France spokesman contacted by the Monitor said the company cannot confirm or deny the authenticity of the document, citing a pending investigation.

When malfunctioning, the Pitot tubes can send incorrect measurements of the aircraft’s speed – a serious problem for pilots in turbulent or extreme weather.

The document suggests that “the AF447 experienced the same problems as all the other aircraft that encountered a Pitot defect, the only difference being that those other aircraft managed to free themselves from that situation,” according to the pilot’s web posting.

The faulty speed sensors were early raised as one of several possible causes for the June 1 AF447 tragedy – along with lightening, electric failure, a malfunctioning rudder, faulty computers, extreme winds, and others.

An assertion by the Eurocockpit posting – also highlighted in the Canard article – is that early on the morning of June 1, Air France authorities knew the Pitot tube had malfunctioned. But in the hours and initial days after the crash, as speculation and the search intensified – the airline did not did not list this among the possible causes. It was not mentioned until June 5.

As noted in an earlier Monitor posting, Le Monde reported on June 6 that Air France pilots were notified by the airline of Pitot tube problems dating back to May 2008.

On June 6, Air France acknowledged that the air-speed monitors on Airbus planes have proven faulty, icing up at high altitude, and that recommendations to change them were first made in September 2007. Air France said it began to gradually replace the monitors on the Airbus A330 model on April 27, 2009.

Many airlines using the Airbus 330 models have since replaced the Pitot tubes as a precautionary step.

The internal document, titled “Treatment of the incidents with loss of the airspeed indication,” offers guidance for pilots should the Pitot tubes malfunction.

It also reveals that the aircraft's manufacturer was aware of and had communicated about the air-speed sensor problem to Air France: “Investigations conducted on Airbus family aircraft showed that most of airspeed discrepancy events were due to Pitot water ingress and to probe draining holes obstructed by external particles,” according to the NT 34-029 document.

The Eurocockpit posting notes that Air France Flight 447 was the 36th reported instance of faulty Pitot tubes, including nine cases in 2009.

The Canard column, by Henri Martin, asserts that ACARS (automatic alert) messages sent from the plane to the ground crew at Charles de Gaulle airport clearly showed the air-speed sensors had malfunctioned, and that Air France mechanics were waiting at the airport to replace them: “There was so little question about the interpretation of [the failure] that a technical team was summoned to wait for the aircraft on Roissy tarmac ... in order to replace them.”

Paul-Louis Arslanian, the head of the French accident investigation agency, BEA, told reporters on June 6 that it was too early to draw conclusions about the role of Pitot tubes in the crash, saying that “it does not mean that without replacing the Pitots ... the A330 was dangerous.”

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