Accident Overview
On 15 May 2019 at 0935 UTC, an Ace Aviation As-tec 13 (registration G-CKUL) sustained a propeller detachment while returning to Shotteswell Airfield, Oxfordshire, following an uneventful local flight. The pilot, the sole occupant, was uninjured. The aircraft was substantially damaged by the loss of the propeller.
Aircraft and Engine Details
The aircraft, manufactured in 2017, is a flex-wing design powered by a single Simonini Mini 3 piston engine. The engine drives a pusher propeller via a reduction drive belt, with belt tension adjustable through an eccentrically-mounted bearing on the propeller driveshaft.
Sequence of Events
At an altitude of approximately 2,100 ft and about 1 nautical mile north of Shotteswell Airfield, the pilot noticed a sudden increase in engine speed. Observing that the pusher propeller had detached, he shut down the engine and initiated a glide descent. A successful power-off landing was carried out at the airfield.
Investigation Findings
Post-flight inspection revealed that the eccentric bearing assembly and propeller had detached at the support bracket due to a fatigue failure of the bearing support. The propeller was not recovered. Following the event, the engine manufacturer, Simonini Racing SRL, issued Security Campaign No. 1 on 31 May 2019, requiring owners and operators of Mini 3 engines to replace the eccentric bearing support before the next flight.