What happened
During flight, the engine of the aircraft experienced a sudden loss of compression and a subsequent drop in power. This degradation was triggered when an exhaust valve in the third cylinder struck the piston surface repeatedly, causing damage to the piston, cylinder, and spark plugs.
Recognizing the loss of engine performance, the instructor pilot determined that an off-airport landing was necessary. Utilizing prior knowledge of the local area and proactive contingency planning, the pilot identified potential landing sites. As the engine's performance continued to decline, the pilot re-evaluated the landing approach. Shortly before touchdown, the pilot identified insufficient clearance ahead and initiated a turn to avoid obstacles. While this maneuver prevented a frontal collision, the low airspeed prevented an effective flare, resulting in the aircraft contacting the ground with substantial vertical force. The aircraft's structure absorbed the impact, and there were no injuries to the occupants.
The investigation
The investigation focused on the mechanical failure within the engine. Investigators determined that the exhaust valve of cylinder 3 had impacted the piston, though it remained unclear whether the valve had stuck in the open position or fractured before making contact with the piston. This mechanical failure was the primary driver of the loss of engine power.