NTSB Identification: LAX97FA291.
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Accident occurred Sunday, August 17, 1997 in VAN NUYS, CA
Probable Cause Approval Date: 05/04/1998
Aircraft: Hefner Pitts S1S, registration: N10HJ
Injuries: 1 Fatal.
NTSB investigators either traveled in support of this investigation or conducted a significant amount of investigative work without any travel, and used data obtained from various sources to prepare this aircraft accident report.
The pilot departed and requested a right-hand departure to the practice area. During the downwind departure he declared an emergency and witnesses observed the aircraft spiraling downward at a 45-degree angle into a residential street. Parts from the aircraft were found some distance from the accident site. The propeller along with the severed crankshaft flange were found still bolted together less part of one propeller blade. Metallurgical examination revealed that a blade had failed midspan due to fatigue. The propeller was being operated above the design rpm red line of 2,700. Additionally, the propeller was being subjected to gyroscopic aerobatic loads. An rpm restriction for the propeller mandated by an airworthiness directive was not placarded on the instrument panel per the AD. The engine was designed for a type certificated helicopter application and was approved for a 3,200 rpm red line.
The National Transportation Safety Board determines the probable cause(s) of this accident to be: the operation of the propeller beyond the design rpm limitations and the resultant gyroscopic loads from aerobatics. Contributing to the accident was the lack of a required instrument panel rpm restriction for the propeller mandated by an airworthiness directive. Full narrative available
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