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Authors: Bill Palmer
Tags: Air France 447 Accident, A330
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were not mentioned in the Info OSV document. A safe attitude and power setting to go to in the event of the loss of automation and/or airspeed indications was also not mentioned. Yet, that key piece of information is what pilots who have successfully flown through the loss of airspeed events report having used in the critical first seconds.
Training by bulletin rarely has lasting effectiveness, and perhaps even less so when the guidance is general in nature and includes only vague corrective actions.
On November 12, 2008 Airbus revised the earlier 2007 service bulletin. Like the earlier version, this version mentioned the improvement that could be provided by the Thales BA probe in relation to water ingestion, but no longer mentioned icing conditions.
Airbus said that there was no solution that could totally eliminate the risk of probe icing, that the three types of probes installed on the Airbus satisfy criteria that are much higher than the regulatory requirements for certification in relation to icing, and provided a reminder of the procedure to be applied in the event of an erroneous airspeed event.
On November 24, 2008 the issue of inconsistent airspeed indications was raised during a meeting between the technical divisions of Air France and Airbus. Air France requested an analysis of the root cause and a technical solution to resolve the issue. Air France suggested that BF Goodrich probes should be fitted, due to an appearance of greater reliability over the Thales models. Airbus confirmed its analysis and agreed to check the option of replacing the Thales probes with BF Goodrich probes.
Meanwhile, other airlines were also experiencing loss of airspeed events. It was not known what caused these events. The leading theories centered around water ingestion that was tossed around inside the pitot by the turbulence that seemed to be a common factor with each event. Many of the airspeed transients were quite short, such that in some cases the crew did not even see what caused the autopilot to disconnect. Others lasted longer (one to three minutes) with flight control law degradation effects, but loss of control had not been a problem. Looking at the flight data from some of these incidents, the loss of airspeed was so sudden that it looked like it could easily be an electronic problem.
At the end of March 2009 (about two months before the accident), Air France experienced two additional events involving the temporary loss of airspeed indication, including their first one on an A330.
On April 3, 2009, in light of these two new cases, Air France once again asked Airbus during a technical meeting to find a definitive solution. On April 15, Airbus informed Air France of the results of a study conducted by Thales. Airbus stated that the icing phenomenon involving ice crystals was a new phenomenon that was not considered in the development of the Thales BA probe, but that probe still appeared to offer significantly better performance in relation to unreliable airspeed indications at high altitude. Airbus offered Air France an “in-service evaluation” of the BA standard to check the behavior of the probe under actual conditions.
Air France decided to extend this measure immediately to its entire A330/A340 long-haul fleet, and to replace all the airspeed probes. On April 27, 2009 (32 days before the accident) an internal technical document was drawn up to introduce these changes . The modification work on the aircraft was scheduled to begin as soon as the parts were received.
The first batch of Thales BA probes arrived at Air France on May 26th, 2009, six days before flight 447 crashed. The first aircraft was modified two days before the accident. At the time of the accident, flight 447, registration number F-GZCP, was fitted with the original Thales AA probes. They were due to be replaced upon the airplane’s return to Paris.
As of November 2009 (five months after the accident) Airbus had identified thirty-two loss of
Training by bulletin rarely has lasting effectiveness, and perhaps even less so when the guidance is general in nature and includes only vague corrective actions.
On November 12, 2008 Airbus revised the earlier 2007 service bulletin. Like the earlier version, this version mentioned the improvement that could be provided by the Thales BA probe in relation to water ingestion, but no longer mentioned icing conditions.
Airbus said that there was no solution that could totally eliminate the risk of probe icing, that the three types of probes installed on the Airbus satisfy criteria that are much higher than the regulatory requirements for certification in relation to icing, and provided a reminder of the procedure to be applied in the event of an erroneous airspeed event.
On November 24, 2008 the issue of inconsistent airspeed indications was raised during a meeting between the technical divisions of Air France and Airbus. Air France requested an analysis of the root cause and a technical solution to resolve the issue. Air France suggested that BF Goodrich probes should be fitted, due to an appearance of greater reliability over the Thales models. Airbus confirmed its analysis and agreed to check the option of replacing the Thales probes with BF Goodrich probes.
Meanwhile, other airlines were also experiencing loss of airspeed events. It was not known what caused these events. The leading theories centered around water ingestion that was tossed around inside the pitot by the turbulence that seemed to be a common factor with each event. Many of the airspeed transients were quite short, such that in some cases the crew did not even see what caused the autopilot to disconnect. Others lasted longer (one to three minutes) with flight control law degradation effects, but loss of control had not been a problem. Looking at the flight data from some of these incidents, the loss of airspeed was so sudden that it looked like it could easily be an electronic problem.
At the end of March 2009 (about two months before the accident), Air France experienced two additional events involving the temporary loss of airspeed indication, including their first one on an A330.
On April 3, 2009, in light of these two new cases, Air France once again asked Airbus during a technical meeting to find a definitive solution. On April 15, Airbus informed Air France of the results of a study conducted by Thales. Airbus stated that the icing phenomenon involving ice crystals was a new phenomenon that was not considered in the development of the Thales BA probe, but that probe still appeared to offer significantly better performance in relation to unreliable airspeed indications at high altitude. Airbus offered Air France an “in-service evaluation” of the BA standard to check the behavior of the probe under actual conditions.
Air France decided to extend this measure immediately to its entire A330/A340 long-haul fleet, and to replace all the airspeed probes. On April 27, 2009 (32 days before the accident) an internal technical document was drawn up to introduce these changes . The modification work on the aircraft was scheduled to begin as soon as the parts were received.
The first batch of Thales BA probes arrived at Air France on May 26th, 2009, six days before flight 447 crashed. The first aircraft was modified two days before the accident. At the time of the accident, flight 447, registration number F-GZCP, was fitted with the original Thales AA probes. They were due to be replaced upon the airplane’s return to Paris.
As of November 2009 (five months after the accident) Airbus had identified thirty-two loss of
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