On July 3, 1995, a Hiller UH-12C (registration N1348Z) operated by Whirlybirds Inc was involved in an aviation accident near Rio Vista, CA. Investigators recorded the probable cause as: The result of a chafing failure of the left anti-torque control cable while the aircraft was in flight. An inadequate preflight inspection by the pilot-in-command, and an inadequate 100-hour inspection by company maintenance personnel were factors in this… This summary draws on records from the U.S. National Transportation Safety Board (NTSB) historical archive.
During a low RPM recovery, a helicopter experienced an uncommanded right yaw. Full left anti-torque pedal had no effect. After a hard touchdown and rebound, the crew landed again. Inspection revealed a separated anti-torque control cable due to severe wear from chafing near the starter.
Incident Description
During a training flight, an instructor was performing a low RPM recovery maneuver when the aircraft began an uncommanded yaw to the right. The instructor attempted to regain control by applying full left anti-torque pedal, but this input had no effect on the yaw. He then lowered the collective, causing the aircraft to touch down hard. The helicopter rebounded and continued to yaw to the right. The instructor applied left cyclic and rolled off the throttle, resulting in a second touchdown.
Inspection Findings
A post-incident inspection revealed that the left anti-torque control cable had separated. A subsequent laboratory examination determined that the cable failure was due to severe wear. The cable had chafed near the bottom of the starter. Investigators noted that the cable was located in an area that could be inspected during a preflight inspection of the aircraft.