Air Accidents Investigation Branch
Summary:
During a flight from Edinburgh Airport to London Heathrow the autopilot and autothrust disconnected. After several minutes the flight crew were able to re-engage them but they disconnected again during the approach. The aircraft landed safely.
The autopilot and autothrust disconnects were caused by severe drift of the aircrafts Inertial Reference System due to vertical shock loads transferred into the system during the takeoff roll. The source of the shock loading was an uneven repair patch on the runway. The nose landing gear shock absorber was found to be over extended, leading to transfer of vertical shock forces into the airframe.
The aircraft manufacturer had investigated previous similar events and published guidance to maintenance organisations but had not published information to flight crew.