What happened
The aircraft was operating on an IFR flight plan and descending through 10,400 feet when the pilot reported engine roughness and vibration. Air traffic control provided radar vectors to an airport located 15 miles away. The pilot reported that the vibration was eliminated by feathering the propeller.
As the aircraft reached approximately 3.5 miles from the airport, the pilot reported field insight. Shortly thereafter, the aircraft struck trees and impacted the ground about 3/4 of a mile from the runway. At the time of the accident, the aircraft's calibrated airspeed during descent was calculated at 147 knots, which significantly exceeded the recommended engine-out airspeed of 87 knots.
The investigation
Investigators found that the #6 cylinder head barrel was cracked approximately 80% around. The aircraft was equipped with several Supplemental Type Certificates (STCs), including a 50% horsepower increase, a full feathering propeller, speed brakes, long-range fuel tanks, and an increased gross weight of 117 lbs.
Analysis of the aircraft's weight revealed that it was 500 lbs over gross weight at takeoff and was 342 lbs over the maximum allowable landing weight at the accident site. While the aircraft had a calculated gliding distance of 22 miles from 10,000 feet at max gross weight and 87 knots, the descent was conducted at much higher speeds.