The aircraft was on a local flight from Thruxton Aerodrome for the purpose of conducting an air test as part of the revalidation of its Permit to Fly. The aircraft was flying at approximately 110 kt and 950 ft amsl when the left door detached without warning. After checking the control response was normal, the pilot returned to Thruxton where the aircraft landed without further incident.
The pilot and the observer stated that they had checked the doors were closed before departure and the observer, who was sitting next to the door, added that there was no flapping or draught to suggest the door had not been properly closed.
The missing door was not recovered, but the failure face on the remaining part of the hinges was reported as appearing “fresh” and no damage was reported in the area of the shoot bolt guides, suggesting that a hinge failure was unlikely. A post-flight inspection identified that the door had struck the left tailplane, causing significant damage. The LAA later reported that there was evidence of the extended rear shoot bolt rubbing on the outside of the door frame.