On November 10, 1998, a Hiller UH-12E (registration N752GB) was involved in an aviation accident near Marshall, WA. Investigators recorded the probable cause as: Separation of the bolt connecting the lower end of the upper-firewall lateral cyclic linkage bellcrank to its push rod, resulting in loss of lateral cyclic control and uncontrolled descent. This summary draws on records from the U.S. National Transportation Safety Board (NTSB) historical archive.
During climb out from a residential helipad, a bolt connecting the cyclic bellcrank to its push rod separated, causing loss of lateral cyclic control and an uncontrolled descent into terrain.
Accident Sequence
While climbing out after takeoff from the helicopter pad located at the pilot's residence and place of business, the bolt that connected the lower end of the upper-firewall lateral cyclic linkage bellcrank to its push rod separated from the aircraft.
With the bolt missing from the control linkage, the necessary increase of the angle of attack (cyclic feathering) of the retreating blade (port blade) could not take place. Without this feathering, which is produced by the lateral position of the cyclic, the forward-moving blade (starboard side) produced considerably more lift than the retreating blade. This resulted in an uncontrolled roll to the left and an uncontrolled descent into the terrain.
Probable cause
Separation of the bolt connecting the lower end of the upper-firewall lateral cyclic linkage bellcrank to its push rod, resulting in loss of lateral cyclic control and uncontrolled descent.
Frequently asked questions
What happened in the 10 Nov 1998 Hiller UH-12E accident near Marshall, WA?
During climb out from a residential helipad, a bolt connecting the cyclic bellcrank to its push rod separated, causing loss of lateral cyclic control and an uncontrolled descent into terrain.
What aircraft was involved and where did it happen?
The accident on 10 Nov 1998 involved a Hiller UH-12E, registration N752GB, at Marshall, WA.
What was the probable cause of the accident?
Separation of the bolt connecting the lower end of the upper-firewall lateral cyclic linkage bellcrank to its push rod, resulting in loss of lateral cyclic control and uncontrolled descent.
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