Oscillations force BA 777 back to Heathrow

The UK air-Accident Investigation Branch is looking into a mysterious in-flight incident involving a British Airways Boeing 777-200A, which was forced to turn back to London Heathrow in October 1996 after suffering uncommanded rudder movement. BA and Boeing have so far failed to replicate the problem.

A UK Civil Aviation Authorityoccurrence report says that the 777, which was en route to Jeddah, experienced "uncommanded movement of rudder and rudder pedals during climb and cruise-at random intervals", which resulted in roll oscillations. The aircraft's flaperons, effectively inboard high-speed ailerons, were also seen by the flightcrew to be moving randomly.

These movements could not be explained, so the crew elected to turn back to Heathrow. It is thought that the flaperons were being activated to counter the uncommanded movement of the rudder. A manual landing was carried out, with "-large rudder input required", says the report.

An initial investigation suspected an intermittent fault in the aircraft's two autopilot flight-director computers. Both were removed and tested, as were the two rudder backdrive activators. o

Source: Flight International