On January 3, 1988, a Bell 47D1 (registration N175K) was involved in an aviation accident near Fontana, CA. Investigators recorded the probable cause as: The separation of a tail rotor blade caused by high cycle fatigue in the tail rotor yoke. This summary draws on records from the U.S. National Transportation Safety Board (NTSB) historical archive.
A helicopter experienced an uncontrolled descent and collided with terrain after a loud bang was heard during a solo instructional flight. Investigation revealed tail rotor blade separation due to high cycle fatigue in the yoke.
What happened
During a solo instructional flight, the pilot reported hearing a loud bang while airborne. Immediately following the noise, the aircraft entered an uncontrolled spinning descent to the right. The helicopter subsequently collided with the terrain.
The investigation
Post-accident examination of the wreckage revealed that one of the tail rotor blades had separated from the tail rotor assembly. A metallurgical analysis was conducted on the tail rotor yoke to determine the cause of the failure.
Findings
The metallurgical examination of the tail rotor yoke indicated that the component failed due to high cycle fatigue. This structural failure led directly to the separation of the tail rotor blade and the subsequent loss of control.
Probable cause
The separation of a tail rotor blade caused by high cycle fatigue in the tail rotor yoke.
Frequently asked questions
What happened in the 3 Jan 1988 Bell 47D1 accident near Fontana, CA?
A helicopter experienced an uncontrolled descent and collided with terrain after a loud bang was heard during a solo instructional flight. Investigation revealed tail rotor blade separation due to high cycle fatigue in the yoke.
What aircraft was involved and where did it happen?
The accident on 3 Jan 1988 involved a Bell 47D1, registration N175K, at Fontana, CA.
What was the probable cause of the accident?
The separation of a tail rotor blade caused by high cycle fatigue in the tail rotor yoke.
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