What happened
During a training flight, the instructor performed a procedure to shut down the right engine and feather its propeller. Although the engine was successfully restarted, the left engine began operating roughly and experiencing significant vibrations. In response, the crew shut down the left engine and feathered its propeller, attempting to maintain level flight using only the right engine.
An attempt was made to restart the left engine, but it failed to produce thrust and instead increased aerodynamic drag, necessitating another shutdown. Shortly thereafter, the right engine began losing power. Despite applying full power, the aircraft type continued to descend. As the crew lowered the landing gear, the aircraft struck the tops of trees during the transition phase. The pilot managed to steer the plane between two residential buildings before impacting an open field. The aircraft bounced across a road and collided with a utility pole, resulting in a post-crash fire. Both pilots successfully evacuated the aircraft through the main cabin door.
Findings
Post-accident inspections at the departure airport revealed two separate pools of oil near the engine positions, with oil trails extending from the parking area down the taxiway and onto the runway. Investigations into both engines revealed that they had both experienced catastrophic failure due to oil starvation. The left engine's crankshaft was broken, and the piston heads were found at the top of their cylinders. Metal fragments were also recovered from the right engine's oil sump.
Evidence suggests the failure was linked to the engine rocker box recovery system. The operator noted that this system requires draining during preflight to prevent hydraulic lock. During the preflight inspection, the instructor believed the drain valves had been closed, but they were actually open. It is believed that the crew either failed to close the valves or the valves were stuck in the open position.