What happened
Shortly after takeoff, the pilot of a Lycoming engine aircraft experienced erratic and uncontrollable propeller RPM. The pilot elected to return to the airport; however, during the descent, the engine began running roughly and eventually lost all power. This resulted in an off-airport landing. Personnel at the Challis airport noted that a large puddle of oil was present in the run-up area following the aircraft's pre-takeoff run-up and departure.
The investigation
A preliminary external examination of the engine assembly revealed a large hole in the crankcase, located adjacent to the number four cylinder assembly. Investigators found that the number four piston rod was fractured. Additionally, extensive heat distress, deformation, and discoloration were observed on both the number three and number four piston assemblies.
Further examination of the engine assembly showed that the hydraulic pump adapter pad cover gasket was protruding from between the accessory mounting pad and its associated cover. A section of this gasket had separated and been displaced from its installed position. An FAA Airworthiness Inspector reported that while the installed gasket is intended for use with a hydraulic pump, this specific engine configuration does not utilize such a pump, meaning a hydraulic pump adapter pad gasket should have been used instead.
Findings
- The fractured piston rod and heat distress to the pistons were noted during the inspection.
- A representative from Textron Lycoming stated that the observed damage is indicative of oil deprivation.
- The use of an incorrect gasket type contributed to the engine's failure.