Boeing 747-4H6, 9M-MPL, 17 August 2012
Boeing 747-4H6, 9M-MPL
Summary:
Significant vibration was noted on the No 2 engine during departure from London Heathrow Airport. The engine subsequently failed and was shut down by the crew who elected to jettison fuel and return to Heathrow Airport. During the approach for a planned autoland, all three autopilots disengaged, the cockpit displays and lights flickered and a series of fault messages were displayed. The resulting electrical failures culminated in a loss of power to one of the electrical AC buses, and many of the systems powered by this bus were lost or degraded. The commander continued the approach, manually flying the aircraft to a safe landing.
The investigation determined the flickering cockpit displays and lights resulted from a series of failures within the aircraft electrical system, primarily caused by a latent mechanical failure in a Bus Tie Breaker. The effect of this latent failure only became apparent when the aircraft electrical system automatically reconfigured for the planned autoland. One Safety Recommendation has been made.
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