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AAIB: final report on B757 pitot blockage incident
10 December 2009

The U.K. AAIB released the final report of their investigation into a serious incident which occurred at Accra, Ghana in January 2009. A Boeing 757 had a blocked pitot tube. On takeoff the pilot noticed a discrepancy in the airspeed indications. He decided to continue the takeoff and deal with the problem whilst airborne. While climbing the crew attempted to isolate the left Air Data Computer from the Autopilot and Flight Director System.
Passing FL316, the VNAV mode became active and the Flight Management Computer’s (FMCs), which use the left ADC as their input of aircraft speed, sensed an overspeed condition and provided a pitch-up command to slow the aircraft. The co-pilot was concerned about the aircraft’s behaviour and, after several verbal prompts to the commander, pushed the control column forward. The commander, uncertain as to what was failing, believed that a stick-pusher had activated. He disengaged the automatics and lowered the aircraft’s nose, then handed over control to the co-pilot. A MAYDAY was declared and the aircraft returned to Accra. The operator’s subsequent engineering investigation discovered the remains of a beetle-like creature in the left pitot system. (AAIB)