What happened
A training flight involving two licensed pilots was being conducted at Baragacia Airfield to facilitate pilot familiarization with single-engine operations. The flight proceeded normally through several successful take-offs and landings while operating with the starboard propeller feathered.
During the approach for a third landing, the aircraft was configured with extended landing gear and flaps set to 60 degrees. The crew noted an unusual noise originating from the port side of the aircraft. Suspecting an issue with the undercarriage, the pilots elected to execute a go-around at speeds between 85 and 90 mph. Upon advancing the throttles to fine pitch, the port engine failed to respond.
As the aircraft lost altitude, the crew retracted the landing gear and feathered the port propeller in an attempt to manage the descent. During this process, the airspeed dropped to between 70 and 80 mph. The pilots then raised the flaps to 20 degrees, but the aircraft continued to sink and experienced a leftward yaw. After passing over a line of trees, the De Havilland Dove entered a stall and struck the ground, despite the starboard engine remaining at full power.
Findings
The investigation determined that the failure of the port engine was caused by a mechanical breakdown within the vibration damper assembly. Specifically, a bolt in the vibration damper had partially unscrewed from its roller. This allowed the rear damper ring to operate directly on the bolt shank, which subsequently failed due to excessive loading.