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Airbus examines possible counter to erroneous airspeed data

Airbus has disclosed that it has been studying a concept to safeguard airspeed information in the event of unreliable air data being received through the regular pitot system.

But the concept, based on alternative airspeed calculation and detailed in an Airbus-affiliated patent, is still embryonic and unlikely to emerge as an operational application in the near term.

Investigation into the loss of Air France flight 447 over the South Atlantic, in June 2009, has highlighted the potential vulnerability of the regular pitot system to icing phenomena.

Air France A330
 © Air France

While the patent is dated September 2009, Flight International understands that the concept, newly published, was originally drawn up before the accident.

The document points out that, in rare instances, icing could overwhelm the pitot sensors and neutralise the normal comparison checks performed by the air data computers to assess airspeed validity.

It says this means pilots "can be without any reliable indication about speed or be unable to eliminate the erroneous speed".

The document outlines a proposal for detecting errors by regularly memorising previously measured airspeeds and using on-board sources of information to calculate a theoretical airspeed.

This calculation would take into account thrust and drag derived from parameters such as mass, altitude, incidence angle, and the configuration of flaps and slats.

"By comparing the current conventional speedwith such an estimated theoretical conventional speed, it is possible to detect a mismatch due to a [conventional] erroneous speed," says the document, adding that the mechanism would provide a "substitution speed" in real time if necessary.

But while the idea appears simple in principle, there are several potential complexities with developing a workable modification to the airspeed system.

It would not only have to deal with the immediate flight parameters but also the effects of the airframe's age and individual modifications.

"It's a long-term development," says Airbus, which adds that the concept is undergoing research at the airframer's facilities. "It's not something that's going to be translated to being operational in the short term."

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