On October 11, 1988, a Cessna 140 (registration N11191) operated by Max D. Ludwig was involved in an aviation accident near Fairfax, OK. Investigators recorded the probable cause as: The separation of the number one cylinder exhaust valve head, which caused an engine lockup. This summary draws on records from the U.S. National Transportation Safety Board (NTSB) historical archive.
A pilot was forced to land in a field after his engine locked up, resulting in a hard impact and a skull fracture.
What happened
The pilot reported that the aircraft engine became locked during flight. In response to this mechanical failure, he executed a forced landing in a muddy, plowed field. The airplane impacted the ground with significant force. As a result of the hard landing, the pilot sustained a fracture to the skull just above his right eye.
The investigation
Following the accident, mechanics performed an engine teardown to determine the cause of the failure. Inspection revealed that the head from the exhaust valve on the number one cylinder had detached and was found sticking sideways in the head of the number one piston. This mechanical interference caused the engine lockup.
Findings
The investigation identified a critical internal engine failure as the primary factor. The separation of the exhaust valve head led to immediate engine seizure, necessitating the emergency landing.
Probable cause
The separation of the number one cylinder exhaust valve head, which caused an engine lockup.