Flight Details
The Bristol 175, also known as the Britannia, had just completed a test flight lasting 1 hour and 40 minutes. The test program included strain-gauge measurements on the non-standard propeller of the no. 2 engine, as well as high-speed upset manoeuvre recovery tests conducted as part of the aircraft's US certification. The flight returned to Filton, where the aircraft entered a circuit pattern.
Accident Sequence
During the approach, partial landing gear extensions occurred for reasons that were not determined. It is possible that attempts were made to complete undercarriage free-fall tests, as these had failed the previous day; however, such tests were not part of the flight's official program. At an altitude of 1500 feet, a left turn to base leg was initiated. Suddenly, the right wing dropped, and the aircraft entered a very steeply banked right-hand turn. The Britannia briefly recovered from this unusual attitude but then banked steeply again and struck the ground in a wooded area near a residential zone.
Probable Cause
The official investigation determined that the accident was the result of the aircraft developing a very steep descending turn to the right which the pilot was unable to control. The reason for this could not be determined, but the possibility that it occurred as the result of malfunctioning of the autopilot cannot be dismissed.