History of the Flight
On 27 November 2018, a Diamond DA42 (N648KM) was en route from Retford Gamston Airport to Weston Airport, Dublin, Ireland, under IFR. The planned cruising level was FL100. Icing was forecast, and the aircraft's anti-icing system had been replenished before departure. The pilot, who held an FAA PPL with an Instrument Rating, reported that pitot heat was on during the climb.
Approximately 39 nm east of BAGSO, the left engine fire warning illuminated. The pilot disengaged the autopilot, retarded the left engine control to idle, and monitored for smoke or flames. The co-pilot contacted Scottish ATC, declared a PAN, and requested descent and vectors to the nearest airfield.
Diversion and Loss of Control
Scottish ATC suggested a diversion to Liverpool Airport and cleared the aircraft to descend to 5,000 ft. The crew squawked 7700 and were handed to Liverpool ATC, who offered vectors for an instrument approach to Runway 09. The fire warning persisted until below 5,000 ft, briefly cleared, then reappeared. No signs of fire were observed.
At approximately 3,000 ft, the pilot re-engaged the autopilot. He later became aware that autopilot use was not permitted for asymmetric flight. Shortly after, he felt a sudden jolt, the autopilot disengaged, and the slip ball moved to full left deflection. The aircraft pitched sharply nose down and descended rapidly. The pilot applied full left rudder, neutralised the control column, retarded the good engine to idle, and gradually pulled back on the control column. The aircraft entered VMC at approximately 800 ft agl over Crosby and was recovered to level flight.
Landing at RAF Woodvale
Liverpool ATC suggested a diversion to RAF Woodvale, which was closer than Liverpool Airport. The crew accepted and were given Woodvale's weather and tower frequency. Woodvale ATC, alerted by Liverpool, cleared the aircraft to land on Runway 03 despite it being out of use due to a degraded surface, given the circumstances. The aircraft landed safely and taxied under its own power.
Analysis
Following the fire warning, the pilot faced asymmetric flight with the left engine at idle. The high workload, IMC conditions, and diversion pressures contributed to a challenging situation. The autopilot, lacking a yaw channel, was unable to control the effects of asymmetry. Its engagement likely exceeded operating parameters, leading to loss of control. The aircraft likely entered a spiral dive due to yaw-induced roll.
Conclusion
Control was lost during high-stress, high-workload flight after an engine fire warning. The pilot probably became spatially disoriented, and autopilot use exacerbated the situation. Recovery occurred as the aircraft reached VMC at low altitude.