Introduction
The Australian Transport Safety Bureau (ATSB) investigated an event where an aircraft experienced a sudden loss of engine power. The investigation focused on the exhaust valve of cylinder 3, which had impacted the piston surface multiple times.
Event Details
The exhaust valve of cylinder 3 impacted the piston surface repeatedly, resulting in damage to the piston, cylinder, and spark plugs. This damage caused a sudden loss of compression and subsequent loss of engine power. The ATSB was unable to determine whether the valve had stuck open, leading to piston impact and valve fracture, or whether the valve fractured before impacting the piston.
Actions Taken
Following the loss of power, the instructor identified that an off-airport landing was required. The instructor's prior knowledge of the area and proactive contingency planning assisted in identifying possible landing locations. As the engine's performance continued to deteriorate, the instructor re-evaluated the decision and changed the plan, including shortly before touchdown when it was assessed that there was insufficient clear area ahead.
Outcome
The turn away from obstacles prevented a potentially significant frontal impact. However, this maneuver also led to the aircraft contacting the ground with substantial vertical force due to the low remaining airspeed, which limited the instructor's ability to flare the aircraft. Fortunately, the aircraft absorbed the vertical impact, preventing significant injury to the occupants.