What happened
On 26 January 2016, a BAe ATP, registration G-BUUR, was conducting a night cargo flight from Jersey to Guernsey. During the approach to Runway 27, the crew encountered strong crosswinds and gusty conditions. As the aircraft approached decision altitude, the pilot flying attempted to disengage the autopilot, but the crew did not hear the expected audio alert. Believing the autopilot remained engaged and sensing stiff controls, the crew initiated a go-around.
During the climb, the aircraft exhibited a significant pitch-up tendency. The pilot flying applied substantial forward pressure on the control column to counteract the nose-up movement, while the pilot not flying instinctively assisted with manual pressure. This period of intense control input coincided with the activation of the Standby Control System (SCS), resulting in the left and right elevators operating in split control. Distracted by these flight control issues, the crew failed to follow standard operating procedures, leading to the delayed retraction of flaps and landing gear. The crew eventually leveled the aircraft, re-engaged the autopilot, and diverted to Jersey for landing.
The investigation
The investigation focused on the cause of the autopilot disengagement failure and the subsequent elevator split. Investigators analyzed flight data from the FDR and QAR, which showed that the autopilot did disengage as commanded, despite the crew's perception. However, the investigation was hampered by the fact that the Cockpit Voice Recorder (CVR) had been overwritten during maintenance before the AAIB was notified.
Technical examinations of the aircraft revealed no mechanical defects that would explain the reported autopilot failure. Investigators also looked into human factors, including the crew's lack of a detailed go-around briefing and the potential impact of fatigue, as the crew's rest period had fallen short of the operator's requirements due to hotel-related issues.