On November 2, 1988, a Cessna 421A (registration N3385Q) was involved in an aviation accident near Cabazon, CA. Investigators recorded the probable cause as: Fatigue fracture of the right engine #3 cylinder head at the threaded area between head and cylinder. This summary draws on records from the U.S. National Transportation Safety Board (NTSB) historical archive.
After losing power on the right engine, a pilot was unable to maintain altitude due to a propeller that did not feather. The aircraft struck an electrical transmission line and collided with a residence after overflying a highway.
Accident Sequence
The pilot contacted the ARSA controller for advisories after experiencing a loss of power on the right engine while overflying an Air Force base. The controller informed the pilot that his position was near a civilian airport with limited maintenance facilities and an Air Force base. The pilot indicated a desire to continue to a larger civilian airport along his route where maintenance service could be obtained.
Subsequently, the pilot reported to the controller that visibility of the ground was poor and that he was unable to maintain altitude because the propeller was not feathering. The aircraft overflew a small civilian airport, and the pilot communicated to the UNICOM operator his intention to attempt a landing on an interstate highway. The aircraft then overflew the highway, impacted an electrical transmission line, and collided with a residence.
Post-Accident Findings
A post-accident inspection revealed that the right engine's #3 cylinder head had fractured, allowing the head to displace outward by 3/8 inch. The fracture resulted from fatigue at the threaded area between the cylinder head and cylinder. The propeller governor was tested functionally after the accident and operated normally.
Probable cause
Fatigue fracture of the right engine #3 cylinder head at the threaded area between head and cylinder