The investigation team currently examining records from crashed AirAsia flight QZ8501 has found evidence suggesting that a key component of the aircraft’s automated control system may have been compromised midflight. Although the glitch would not have directly caused QZ8501 to crash, it could have forced the pilots to fly the plane manually in a highly stressful situation.

While analyzing data records retrieved from the aircraft’s black boxes, the investigation team found a reason to look into the possibility of the aircraft’s Flight Augmentation Computers, or FAC, encountering a glitch during the flight. The FAC is an important component of the plane’s overall automated control system. It is responsible for controlling a plane’s rudder movements and helps keep the plane stable. The FAC also detects changes in wind speed or direction and adapts the plane’s movements to outside factors accordingly, keeping the plane well within its flight envelope.

Failure of both the primary and backup FAC is a very rare occurrence. Without the twin FAC system, the pilots of QZ8501 had to rely on manual flying under stressful weather conditions, which they may have been ill-prepared for. Indonesian officials said it appears that after the pilots encountered a storm and requested approval to fly higher, the Airbus A320 accelerated rapidly and stalled before plunging into the Java Sea. If there was a problem with the aircraft’s FAC system, this could explain why the plane was unable to automatically correct itself before entering a stall.

Indonesia’s National Transportation Safety Committee has not commented on the accuracy of these speculations about QZ8501’s FAC system. However, Indonesian magazine Tempo reports that one of QZ8501’s pilots complained about a maintenance problem with the rudder system of the exact same aircraft days before the flight. Photos of the wreckage neither prove or disprove that a problem with the rudders caused the crash.

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