Another Airbus 330 incident; is the aircraft safe?

Posted on 02. Nov, 2009 by in Airline Safety, Blog

Following the tragic loss of Air France 447, the published EASA (European Aviation Safety Agency) fix for the Airbus 330 was to replace the Thales pitot systems with Goodrich versions.  Pitot systems are a critical flight instrument system that measure indicated airspeed of an aircraft.  Here is the problem: the Jetstar A-330 that just experienced bad input to ADIRU #1 had the Goodrich systems installed.  As I have pointed out in past articles the single point of failure, in my opinion, is not the pitot system it is the ADIRU #1.  The air data inertial reference units are the process point for the various inputs; airspeed, angle of attack, etc.  Two other ADIRUs (#2 and #3) also collect the same data.  The fly by wire system is designed so that the three units communicate with each other and if one unit’s data is out of parameters it is dropped from the overall system.

The Australian Transportation Safety Board’s (ATSB) initial finding, on Qantas Flight 72’s A-330 incident, determined it was a false angle of attack input passed by ADIRU #1 to the primary flight computer that caused the subsequent loss of control and injuries.  ADIRU #1 would not automatically deselect, even after the flight crew switched the system to ADIRU#2.  It sent flawed inputs to the flight computer which caused the fly by wire system to overstress the airframe with spurious inputs.  Procedures were issued by the EASA and yet on a subsequent Qantas flight they failed to override ADIRU #1.  New procedures were then issued by the EASA to de-energize ADIRU #1 to prevent it from passing spurious data to the primary flight computer.   The European Aviation Safety Agency (EASA) issued two Emergency Airworthiness Directives (EAD) involving the ADIRU in December and January following the Qantas incidents.

In light of the ATSB’s findings and EASA issued procedures, I was totally confused by the focus on the pitot system after the Air France 447 accident.  The ATSB made it very clear that it was a separate system, the angle of attack system, which caused the QF 72 upset.  In short, it was my opinion that they were treating the symptom not the cause.  My opinion has not been swayed that it is the ADIRU #1 that is the common denominator in these incidents.  The recent problem with the Goodrich system seems to verify this.  Since it is apparent that the fix was not a fix; the question remains.  Is the A330 safe?

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