What happened
After completing 45 minutes of local banner-towing operations, the pilot began the return flight to the airport. During the flight, the pilot advanced the throttle to begin a climb, but the engine failed to respond. As the engine lost power, smoke was observed emerging from beneath the cowling.
While monitoring the instruments, the pilot noted that the RPM was decreasing and the oil temperature was approaching the red line, though the oil pressure remained steady at 80 psi. The pilot subsequently executed an emergency landing in a field. Upon touchdown, the aircraft's right wing struck a tree.
The investigation
Post-accident examination of the engine identified a hole burned through the top of the #3 cylinder. This damage was found to be consistent with detonation.