Programmers missed one bug in the Boeing 777 autopilot. Passengers on Flight 124 survived the roller coaster ride.
The passengers and crew of Malaysia Airlines Flight 124 were just settling into their five-hour flight from Perth to Kuala Lumpur that late on the afternoon of 1 August 2005. Approximately 18 minutes into the flight, as the Boeing 777-200 series aircraft was climbing through 36 000 feet altitude on autopilot, the aircraft—suddenly and without warning—pitched to 18 degrees, nose up, and started to climb rapidly. As the plane passed 39 000 feet, the stall and overspeed warning indicators came on simultaneously—something that’s supposed to be impossible, and a situation the crew is not trained to handle.
At 41 000 feet, the command pilot disconnected the autopilot and lowered the airplane’s nose. The auto throttle then commanded an increase in thrust, and the craft plunged 4000 feet. The pilot countered by manually moving the throttles back to the idle position. The nose pitched up again, and the aircraft climbed 2000 feet before the pilot regained control.
The Australian Transport Safety Bureau investigation discovered that the air data inertial reference unit (ADIRU)—which provides air data and inertial reference data to several systems on the Boeing 777, including the primary flight control and autopilot flight director systems—had two faulty accelerometers.
when the second accelerometer failed, a latent software anomaly allowed inputs from the first faulty accelerometer to be used, resulting in the erroneous feed of acceleration information into the flight control systems. The anomaly, which lay hidden for a decade, wasn’t found in testing because the ADIRU’s designers had never considered that such an event might occur.
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