History of the Flight
On 14 February 2018, a BAE Systems ATP, registration SE-MHE, operated a commercial air transport cargo flight from East Midlands Airport to Guernsey Airport. The aircraft was crewed by a line training captain (commander) and a pilot under training (PUT). Both pilots reported for duty at 0345 hrs after three days of rest. The commander had 8,500 total flying hours, including 6,500 on type; the PUT had 4,100 hours, with 12 on type. Pre-flight inspection revealed frost, so de-icing was performed.
The aircraft departed from Runway 27 at 0551 hrs. The autopilot was engaged at 1,000 ft and the flight continued to a cruising altitude of FL 180. No visible icing was observed; total air temperature was -14°C and outside air temperature -22°C.
Before the top of descent, control was handed to the PUT. He reduced power normally and set approximately 50% torque. Using the autopilot pitch trim wheel, he initiated descent and engaged IAS mode, then vertical speed mode at about 1,000 fpm. As was normal, the slip indicator ball moved left. The PUT used rudder trim anticlockwise to balance the aircraft, but the ball remained left. The trim caution light illuminated, and shortly afterward the autopilot disconnected automatically.
The aircraft immediately rolled 45° left and pitched nose-down. The commander took control, closed both power levers, leveled the wings, and raised the nose. He found the elevator normal but the rudder stiff. Aileron and rudder trims were also stiff, though pitch trim worked. The crew transmitted a MAYDAY, reporting control problems and inability to increase power. ATC offered alternate airports, but the crew elected to continue to Guernsey. After about three minutes, the commander was able to advance the power levers, initially with notchy movements, then normally. The crew conducted an ILS approach to Runway 09 and landed uneventfully at 0701 hrs.
Crew Background and Experience
The PUT began flying in 1999, held a Flight Instructor qualification, and had flown Shorts 330/360, Citation Bravo, and other types before converting to the ATP. The commander started flying in 1998, held an Airline Transport Pilot License, and had extensive experience on Beech 90/200, Piper Cheyenne, Dassault 2000, and the ATP since 2008.
Commander's Recollection
The commander observed the ball moving left and instructed the PUT to trim more. When the autopilot disconnected, he took control. The aircraft was out of trim, stiff on aileron, and pitching down with left bank. He retarded power levers fully and trimmed with stiff controls. He attempted asymmetric power but found the left thrust lever jammed; then the right lever also jammed. The standby engine control system did not increase power. Both engines indicated zero torque. The commander suspected ice on the power control cables. He tried every 20 seconds to operate controls, hoping they would free at lower temperature. He prepared for a glide approach, estimating a 46 nm glide range with Guernsey 43 nm away. When the cables began to unfreeze, he advanced power slightly and informed ATC. On touchdown, controls moved normally.
Recorded Information
The aircraft was equipped with a cockpit voice recorder (CVR) and a flight data recorder (FDR). Data analysis confirmed the sequence of events but lacked parameters like control column position, trim positions, and power lever positions due to the age of the FDR installation.
Investigation Findings
The initial control upset may have been caused by the crew applying aileron trim instead of rudder trim while attempting to correct yaw. The cause of the stuck power controls could not be established definitively. It is possible that the left power lever was restricted due to wear in the roll-over lever locking mechanism, but this would not explain the locking of the right power lever. The manufacturer took action to improve the effectiveness of an existing Service Bulletin related to wear in the locking mechanism and an electronic Service Information Leaflet regarding moisture purging from engine control cables.