Accident Details
The airplane impacted the ground in a nose-low, inverted attitude. The pilot reported over the radio, 'Jeff Tower, N34TM, I've just lost power on the right engine, eh, left engine.' At the time, the airplane's altitude was approximately 200 to 400 feet when its wings wobbled back and forth. Subsequently, the wings banked approximately 90 degrees to the left, and the airplane nosed over before impacting the ground. White smoke was observed emanating from the belly of the airplane for 1 to 2 seconds, approximately 20 seconds prior to impact.
Terrain and Wreckage
The terrain consisted of a flat, hard-packed field used for growing grass sod. Both the left and right propellers were found embedded 12 to 18 inches under the hard-packed soil. Rotational paint transfer patterns from the propeller blades onto the soil were evident, and the propeller blades exhibited chordwise scratching and leading edge polishing.
Engine Examination
Examination of the left engine revealed that the #2 cylinder piston was broken, with the piston pin still attached to the piston rod. The NTSB Materials Laboratory examination determined that the fracture face of the #2 exhaust valve stem was consistent with a bending fatigue separation. Additionally, both the #2 and #6 exhaust valve guides showed heavy wear, resulting in ovalized bores.
Maintenance History
The most recent annual inspection, conducted on March 15, 1999, recorded the following compression readings for the left engine: 80/64, 50, 67, 70, 69, and 62.
Probable Cause
The official probable cause was the pilot's failure to maintain control of the airplane, with a contributing factor being the partial loss of power due to the exhaust valve fatigue failure.