NTSB Identification: SEA05LA170.
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Accident occurred Saturday, August 13, 2005 in Challis, ID
Probable Cause Approval Date: 03/28/2006
Aircraft: Piper PA-24-250, registration: N6677P
Injuries: 2 Serious.

NTSB investigators may not have traveled in support of this investigation and used data provided by various sources to prepare this aircraft accident report.

The pilot reported that shortly after takeoff, the propeller RPM became erratic and uncontrollable and he elected to return to the airport. He reported that during the descent, the airplane developed a rough running engine and eventually lost power resulting in an off airport landing. Preliminary external examination of the assembly revealed a large hole in the engines crankcase, adjacent to the number four cylinder assembly. The number four piston rod was fractured and extensive heat distress, deformation and discoloration was noted to both the number three and number four piston assemblies. A representative from Textron Lycoming reported that this type of damage is indicative of oil depravation. Further examination of the engine assembly revealed that the hydraulic pump adapter pad cover gasket was protruding from between the accessory mounting pad and its associated cover. A section of the gasket separated and was displaced from its installed position. The FAA Airworthiness Inspector overseeing the examination reported that the installed gasket was intended to be used in conjunction with a hydraulic pump, if applicable, however, this particular engine configuration does not utilize a hydraulic pump, and therefore a hydraulic pump adapter pad gasket should have been installed. Personnel at the Challis airport reported that a large puddle of oil was found in the run-up area following the airplane's pre takeoff run-up and departure.

The National Transportation Safety Board determines the probable cause(s) of this accident to be:

The installation of an improper oil gasket by maintenance personnel, which resulted in a loss of engine oil and subsequent loss of engine power during the emergency descent.

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