The Civil Aviation Safety Authority has just issued an urgent airworthiness directive affecting all 21 Airbus A330 wide bodied jets flown by Qantas (15) and Jetstar (6).

CASA says that in lay terms, pilots must now follow revised procedures to isolate a faulty Air Data Inertial Reference Unit or ADIRU like the one that imitated the malevolent computer HAL in the sci-fi classic 2001 (to insert our own colorful metaphor) in the emergency diversion and landing of Qantas flight QF 72 at Learmonth on 7 October.

The new procedures also put important limits on the transfer of fuel between tanks on the airliner for purposes of maintaining correct trim in the event that such a failure has occurred. It is not clear if this part of the directive refers to something that the Qantas pilots did in the course of bringing the flight safely to the remote airport.

There are three Northrop-Grumman ADIRUs on the A330. They are supposed to ‘vote’ and override a malfunctioning unit, and finding out why this did not happen on this flight is a key element of the investigation by the Australian Transport Safety Bureau in conjunction with French and US authorities, and Qantas and Airbus.

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