The aircraft departed London Gatwick at 17:28 with an estimated time of arrival at East Midlands of 18:25. The crew included two pilots and a cabin attendant, in accordance with Dan-Air's policy to carry one attendant in addition to the flightdeck crew on mail flights. During its initial descent towards its destination, the attendant reported that one of the cabin door's indicators was showing an unlocked condition. Shortly afterwards, the right hand rear door opened, detached itself from its hinge mounts and became lodged on the leading edge of the right horizontal tailplane. Later reconstruction of the aircraft's flight path from flight recorder evidence indicated that cabin decompression occurred when it was in the vicinity of Market Bosworth. The aircraft became uncontrollable and went into a steep dive, which terminated in several abrupt pitch oscillations. Immediately after the decompression, the pilot asked the co-pilot to transmit a "MAYDAY" and request permission from air traffic control to come straight in for an emergency landing, reporting that he thought he had lost the rear door and that he was having severe control problems. Shortly after, the radar controller who handled flight 240 noticed that the aircraft was turning right beyond its assigned heading; however, his attempts to contact the crew proved futile. Approximately three minutes after the last distress message, reports began to reach ATC from the police of an aircraft crash. Several people on the ground witnessed the final moments of flight 240. The consensus of their evidence was that the stricken plane was lower than usual compared with other aircraft approaching East Midlands, and that it was losing altitude as well as oscillating in both pitch and roll. As it regained level attitude, both wings folded up almost simultaneously and became detached from the fuselage, along with other parts of the structure. The wreckage was found scattered across several fields, approximately northeast of the village of Nailstone.
Cause
It was concluded that the accident had been caused by the baggage door becoming lodged on the leading edge of the right tailplane after it had opened and detached. This changed the aircraft's aerodynamic characteristics so that it became uncontrollable. This in turn resulted in overstressing of the wings and tailplane leading to inflight structural failure, with both wings and tailplane detaching from the fuselage. Contributory factors were the mis-rigged state of the door operating mechanism, which allowed the top and bottom pairs of catches to lose synchronisation, and failure of the door warning indicators to give the crew enough time to respond to door safety alerts.
