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September 17, 2005
Software hijacks jet airliner ... again?
In today's Australian there's a chilling story about the pilots of a Malaysian Airlines 777 flying from Perth to Kuala Lumpur last month battling to regain control after an "unknown computer error" caused the aircraft to pitch violently, and brought it close to stalling.
An Australian Transport Safety Bureau report released yesterday reveals the pilot in command disconnected the autopilot and lowered the plane's nose to prevent a stall, after incorrect data from a supposedly fail-safe device caused the plane to pitch up and climb 3000ft, cutting its indicated air speed from 500kmh to 292kmh, activating a stall warning and a "stickshaker". [A stickshaker vibrates the aircraft's controls to warn the piot when he is approaching stall speed ... which, you know, means the plane is about to fall out of the air.]
The system refused to give up control, however. It increased the power on the automatic throttle, forcing the pilot to counter by pushing the thrust levers to the idle position. The aircraft immediately pitched up again, and climbed 2000ft.
The pilot turned back to Perth under manual control. When he kicked in the two autopilot systems, the plane banked to the right, and the nose pitched down. He resumed hands-on control.
But on its landing approach, at 3000ft, the flight display gave a low airspeed warning and the auto-throttle increased thrust. The warning system also indicated a dangerous windshear, but the crew landed the jet safely.
According to the report, "investigations are focusing on faulty acceleration figures suppied by a device called the Air Data Inertial Reference Unit". The ADIRU, which was developed by Honeywell, collates aircraft navigation and performance data from other systems and passes the information to the primary flight computer. The buggy software, unfortunately, allows data from faulty sensors to enter the "fault-tolerant" system.
What's potentially more disturbing, however - and this isn't in the newspaper report - is that a US FAA directive in June this year highlighted other problems with the Boeing 777's ADIRU. That was followed by another directive - possibly inspired by the Malaysian Airlines incident - which introduced interim measures to deal with what the FAA identified as an unsafe condition.
A local Boeing spokesman, Mr Ken Morton, says the company has told operators of the jet - which by the way has the best safety record of any aircraft - to load a previous software version, according to The Australian's report. But as the FAA's directive indicates, that previous version also has problems.
Mr Morton claimed the [Perth] incident "hadn't occurred before or since", which doesn't gell with the FAA directive. And it raises a lot of questions as to why a condition identified in January this year should have recurred even more dramatically in August.
So while we're trusting that the pilots and operators aren't taking quite the same "no problems" attitude indicated by Ken Morton in this report, we're going to avoid travelling in any Boeing 777 aircraft in the immediate future.
Posted by cw at September 17, 2005 10:39 AM