What happened
On 4 October 2003, a Cessna 172N Skyhawk, registration G-BUAN, was participating in a Fleet Air Arm Squadron fly-in event. While en-route from Lands End to the Scilly Isles at 2,000 feet, the aircraft's engine ceased operation without prior warning. The pilot attempted standard engine failure procedures, but the engine could not be restarted. After notifying St. Marys ATC of the intention to ditch, the pilot brought the aircraft down onto a wave crest into a 12 kt headwind.
Following the impact, the passengers managed to exit the aircraft quickly. However, the pilot became momentarily trapped after catching his foot on the cockpit coaming, only freeing himself once the aircraft had submerged to a depth of roughly 10 feet. The occupants were rescued by a nearby fishing vessel and subsequently airlifted to a hospital by a search and rescue helicopter. The aircraft sank and was not recovered. There were two minor injuries recorded among the three people on board.
The investigation
The investigation examined the circumstances surrounding the sudden loss of power. At the time of the incident, all aircraft in the group had sufficient fuel for the mission, and no other aircraft flying at similar altitudes reported issues with carburettor icing. The fuel selector was found to be set to both tanks. Investigators looked into the possibility of a mechanical failure within the engine's ignition system, specifically noting that the rapid nature of the failure suggested a potential issue with the magneto drive. While later engine models utilize a double drive to prevent such occurrences, the investigation could not entirely rule out other unidentified mechanical problems.