NTSB Identification: CHI07IA017.
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Incident occurred Tuesday, October 24, 2006 in Sherman, IL
Probable Cause Approval Date: 03/31/2008
Aircraft: Piper PA-24-250, registration: N6090P
Injuries: 1 Uninjured.
NTSB investigators used data provided by various sources and may not have traveled in support of this investigation to prepare this aircraft incident report.
The pilot executed a forced landing when the airplane experienced a total loss of engine power during cruise flight. Examination of the engine crankshaft and attached rod components revealed that both nuts on the number three connecting rod were backed off from their original installed positions. One nut on the number four connecting rod had also backed off but had not failed. Bolt preload is related to installation torque but with many variables such as lubrication, thread deformities/variations, rough surfaces, and contamination. Torques tests showed a variance of 18-25 percent of torque values between the tightening and loosening of the nut. The breakaway torque values were within the range of the test values for properly torqued nuts; however due to the uncertainty of the readings no conclusion can be drawn as to the adequecy of the original installation torque. Also, no measurements were possible on the separated number three rod and the damaged number four nuts.
The National Transportation Safety Board determines the probable cause(s) of this incident to be: The loose connecting rod bolt due to a loss of torque and subsequent failure of the connecting rod during cruise flight. Full narrative available
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