As some of you may be aware, on October 7th 2008 a QANTAS A330 traveling from Singapore to Perth was about 154km west of Learmouth, West Australia when it entered a rapid descent, causing unsecured items & people to float up in the cabin, leading to injuries on board. The aircraft declared an emergency and diverted to Learmouth.
The ATSB has released a preliminary finding that states that a fault in one of the Air Data Inertial Reference Units (ADIRU #1) led to the incident. Investigations are continuing and QANTAS have instigated changes in their procedures should the symptoms appear again.
Well, guess what, the symptoms have appeared again! On Dec 27th, a QF A330 going from Perth to Singapore had a similar ADIRU problem in a similar part of the world (this time about 650 kilometers south of Learmouth). Fortunately the crew were able to enact the revised procedures and disconnect the systems, avoiding any upsets. They then decided to return to Perth.
The ATSB says it’s too early to draw conclusions but they note that it is the same problem and also that it occurred in a similar area to the previous incident. As such, they will include this incident in the investigations being performed for the Oct 7th incident which should produce a factual report about mid February.
One of the more interesting aspects of the Oct 7th incident is that the potential was raised for possible external influence on the ADIRU due to either portable electronic devices on board (laptops, mp3 players, etc) or from the Harold E Holt Naval Communications Station near Learmouth (there’s also a Wikipedia article on the comms station).
The situation gets even more interesting if you note that a Malaysian Airlines 777 had a similar ADIRU fault back in 2005 (PDF) in roughly the same area. Of course, the 777 has a different ADIRU, different software and the problem was traced to failed accelerometers and a software fault, but still – very interesting.
Hmmmm – I wonder if the military have been experimenting with something and accidentally zapping ADIRUs every now and again? (cue X-Files theme…).