On January 8, 1983, a Hiller UH-12E (registration N4027D) was involved in an aviation accident near Near Vacaville, CA. Investigators recorded the probable cause as: The pilot's failure to maintain adequate clearance from a telephone wire during takeoff, which led to a precautionary landing on unstable terrain and subsequent ground contact with the rotor system. This summary draws on records from the U.S. National Transportation Safety Board (NTSB) historical archive.
A helicopter struck a telephone wire during takeoff, prompting a precautionary landing on a levee bank that collapsed, causing the aircraft to slide into a ditch and sustain rotor damage.
What happened
The aircraft experienced an in-flight collision with a telephone wire while climbing out during the initial phase of flight. Following the impact, the pilot elected to execute a precautionary landing on the soft, earthen bank of a nearby levee. The primary objective was to assess the extent of structural damage to the airframe and rotor system.
After bringing the aircraft to a stop, the pilot reduced the rotor RPM to idle. However, the ground beneath the helicopter lacked sufficient bearing capacity to support its weight. The soil on the levee bank failed under the load, causing the helicopter to slide uncontrollably down the slope and into an adjacent drainage ditch.
During this uncontrolled descent, the main rotor blades struck the ground surface. This secondary impact resulted in significant damage to the rotor assembly. The pilot later acknowledged that the initial decision to operate so close to the overhead utility lines was a contributing error.
Probable cause
The pilot's failure to maintain adequate clearance from a telephone wire during takeoff, which led to a precautionary landing on unstable terrain and subsequent ground contact with the rotor system.