On September 6, 1995, a Hiller UH-12C (registration N1348Z) was involved in an aviation accident near Porterville, CA. Investigators recorded the probable cause as: the flight instructor's inadequate supervision of the flight; the dual student's improper use of the flight controls; and improper remedial action. This summary draws on records from the U.S. National Transportation Safety Board (NTSB) historical archive.
A dual student inadvertently applied aft cyclic, then raised the collective abruptly, causing the helicopter to climb and lose main rotor RPM. The CFI's autorotation resulted in a hard landing.
Incident Sequence
During a training flight, a dual student attempted to bring the helicopter to a hover. The student inadvertently applied aft cyclic input, causing the helicopter to begin moving rearward. To correct this, the student abruptly raised the collective. The helicopter climbed to approximately 18 feet above ground level, and the main rotor RPM began to decay.
The certified flight instructor (CFI) assumed control of the helicopter and lowered the collective in an effort to regain main rotor RPM, but was unsuccessful. The CFI then performed an autorotation. Due to the decaying main rotor RPM, the helicopter sustained a hard landing during the autorotation.
Findings
The helicopter did not experience any preimpact malfunctions or failures.