On April 22, 1995, a Bell UH-1B (registration N39SD) was involved in an aviation accident near Walla Walla, WA. Investigators recorded the probable cause as: TOTAL FAILURE OF THE FREEWHEELING SPRAG UNIT. A FACTOR TO THE ACCIDENT WAS: SUITABLE TERRAIN WAS NOT AVAILABLE FOR LANDING. This summary draws on records from the U.S. National Transportation Safety Board (NTSB) historical archive.
A helicopter shuddered and made scraping noise during external load lift, followed by low rotor RPM. Pilot released load and attempted emergency landing but collided with trees. Investigation found freewheeling one-way clutch assembly failed due to wear and brinelling.
Accident Sequence
The pilot reported that while conducting an external load operation, the helicopter experienced a shudder and a loud scraping noise immediately after the load cleared the ground. The rotor RPM subsequently dropped to a low level. In response, the pilot released the load and commenced maneuvering for an emergency landing. During this maneuver, the helicopter collided with trees.
Post-Crash Inspection
Following the accident, an inspection of the helicopter revealed that the freewheeling one-way clutch assembly had failed during the flight. The clutch assembly showed signs of wear, and the inner clutch race exhibited brinelling. The worn condition and brinelling marks on the inner race were consistent with the observed failure of the assembly.
Frequently asked questions
What happened in the 22 Apr 1995 Bell UH-1B accident near Walla Walla, WA?
A helicopter shuddered and made scraping noise during external load lift, followed by low rotor RPM. Pilot released load and attempted emergency landing but collided with trees. Investigation found freewheeling one-way clutch assembly failed due to wear and brinelling.
What aircraft was involved and where did it happen?
The accident on 22 Apr 1995 involved a Bell UH-1B, registration N39SD, at Walla Walla, WA.
What was the probable cause of the accident?
TOTAL FAILURE OF THE FREEWHEELING SPRAG UNIT. A FACTOR TO THE ACCIDENT WAS: SUITABLE TERRAIN WAS NOT AVAILABLE FOR LANDING.
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