Hiller UH-12E N36MV accident near Los Banos, California

Probable cause

A partial loss of engine power due to a failure of the throttle interconnect hardware, which resulted in a hard landing.

NTSB analysis

The pilot of the helicopter had just completed an aerial application flight and was returning to land. As he approached the landing area, he began to apply power, but the engine did not respond. He continued to twist the throttle, but it felt loose with no resistance and the engine speed did not change. He aborted the landing approach and performed a run-on landing in a field; during the approach the engine speed began to decrease and the helicopter landed hard, causing substantial damage to the tail boom and lower fuselage. Postaccident examination revealed that the throttle control attach fitting located in the aft section of the collective control had become separated. The nuts and bolts attaching the fitting were not located. The lack of witness marks on the throttle fitting indicates that either the attachment bolt failed or rapidly unscrewed from its associated nut. The disconnection resulted in a loss of engine control and subsequent partial loss of engine power. The last annual inspection occurred 11 months and 250 flight hours prior to the accident.

Text from the NTSB. Open the NTSB docket for WPR10LA127 for the full record.