NTSB Identification: SEA04LA033.
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Accident occurred Tuesday, January 13, 2004 in Enumclaw, WA
Probable Cause Approval Date: 06/30/2004
Aircraft: Cessna 172RG, registration: N64ML
Injuries: 2 Uninjured.
NTSB investigators may not have traveled in support of this investigation and used data provided by various sources to prepare this aircraft accident report.
During a power-on stall sequence the aircraft's engine experienced a significant partial power loss, followed by the engine oil pressure dropping to zero. Since there was no suitable landing area directly below the area where the power loss occurred, the pilot headed to the south and attempted to land on what appeared to be the only available reasonably safe terrain. Based upon his quick evaluation of the landing site, the pilot chose to leave the gear fully retracted. Although the initial touchdown was uneventful, soon thereafter the aircraft contacted the rough/uneven terrain in a manner that resulted in substantial damage to the airframe. A post-accident inspection of the engine revealed that the crankcase mating flange was cracked in two different places, and the number three cylinder push rod and push rod tube were bent in a manner consistent with compression of the pushrod from its ends. The heads of six of the eight cam followers had fractured, the crankcase surface behind all but two of the follower heads was dented and gouged, and the crankcase surface behind two of the heads had small chunks of fractured steel imbedded/crushed into the metal of the case. Removal of the oil pan revealed about a dozen pieces of metal that were clearly identifiable as sections of the cam follower heads. Further inspection of the engine and its cylinders could not determine the initiating event leading to the fracturing of the cam followers.
The National Transportation Safety Board determines the probable cause(s) of this accident to be: A loss of engine power while maneuvering due to the failure of the heads of six of the eight cam followers. Factors include the pilot's decision to keep the gear retracted during the forced landing, and the rough/uneven terrain. Full narrative available
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