Accident Sequence
A witness observed the airplane take off from the end of runway 34. About halfway down the runway, the airplane emitted a sound like a rapid misfire, a pop, and then no audible engine sounds. At that point, the airplane was about 300 to 400 feet above ground level. The witness stated that the airplane turned right, then left to a bank where the wing was straight down. The wings then leveled, the airplane descended, and it impacted terrain. The time from the sounds to the impact was about two to three seconds. The airplane was destroyed on impact with terrain during a forced landing following the in-flight loss of engine power.
Examination Findings
An on-scene examination revealed no airframe pre-impact anomalies. Examination of the engine revealed a cracked crankshaft propeller flange. The engine, without the turbochargers and with the original crankshaft, was test run up to 2,100 RPM. A propeller and governor inspection revealed no anomalies. Examination of the turbocharger system's exhaust bypass valve assembly revealed its butterfly valve was stuck (bound) in the extended closed position. The cracked crankshaft was removed and a serviceable crankshaft was installed. The engine was test run again with a serviceable exhaust bypass valve assembly and produced rated power. The original exhaust bypass valve assembly was reinstalled, and the wastegate bound again during an engine run, with a loss of engine power observed. Sectioning of the bypass valve assembly revealed a bent wastegate shaft. The valve assembly lever arm was bent and exhibited pre-impact tool marks consistent with pliers loosening a bound wastegate shaft.
Maintenance and Documentation
The airplane's pilot operating handbook and FAA-approved airplane flight manual (POH) stated: "ENGINE POWER LOSS DURING TAKEOFF If sufficient runway remains for a normal landing, leave gear down and land straight ahead." The engine manufacturer's maintenance and operator's manual stated that the wastegate is required to be checked for operation and condition during 100-hour inspections but did not specify a procedure for maintenance personnel on how to check the wastegate's operation and its acceptable condition. National Transportation Safety Board Recommendation A-94-081, issued to the FAA in 1994, recommended requiring the amendment of pilot operating handbooks and airplane flight manuals applicable to aircraft equipped with engine turbochargers by including in the 'Emergency Procedures' section information regarding turbocharger failure, including procedures to minimize potential hazards relating to fire in flight and/or loss of engine power. The airplane's POH, latest revision dated October 14, 2002, did not contain information, procedures, or amplified procedures on turbocharger failures. The airplane had accumulated 8.7 hours of operation since the last annual inspection.