Aircraft Accident/Incident Report

Mayville, New York 14757
Friday, August 25, 2000 6:20 EDT

The airplane climbed to 4,000 feet. After level-off, the pilot checked that the gauges were 'in the green,' set the power to 2,400 rpm and 24 inches of manifold pressure, and engaged the autopilot. The engine was running smoothly, with no vibrations. About 35 to 40 seconds later, there was a loud explosion, and blue and yellow flames emanated from both sides of the engine compartment. The pilot turned the airplane towards a field he had seen earlier. During the turn, there was a second explosion. The engine, which had continued to run smoothly after the first explosion, quit. The cabin became engulfed in black smoke, and forward visibility was nil. The pilot then made a forced landing, but due to limited visibility out the side window, the airplane struck trees during the approach, stalled, and hit the ground. Post-accident investigation revealed fire damage to the accessory section of the engine, the firewall, and the interior surface of the left engine cowling. Unburned oil residue was found on the interior surface of the right engine cowling. Oil was also found on the undersides of the fuselage and wings. The oil filler tube, on the right side of the engine, was burned away; however, the majority of the oil dipstick was still in place, in the engine. The interior surface of the left cowling was sooted and scorched. The bottom plate of the engine driven fuel pump was burned away, and the fuel boost pump was sooted. There was a breach in the engine casing, in the vicinity of the number 6 connecting rod. All of the connecting rod ends exhibited heat damage, consistent with a loss of lubrication, with the most severely damaged being the number 6 rod end. The oil pump housing and impellers exhibited light scoring. The main bearings were undamaged. The pilot stated that during his preflight inspection, he checked three times that the oil cap was secure. Additionally, no oil leaks were found on the ramp. Another pilot, with the same airframe/engine configuration as the accident airplane, reported that his oil cap had come loose during flight on several occasions. However, even though it came loose, there was no oil leakage.

An engine compartment explosion due to a fuel/fuel vapor leak of undetermined origin. A secondary explosion resulted from a lack of lubrication to the number 6 connecting rod bearing. Contributing to the pilot's injuries was his reduced visibility during the forced landing, resulting from a heavy concentration of smoke in the cockpit.