On May 4, 1988, a Hiller UH-12E (registration N62391) operated by Pingrey Bros. was involved in an aviation accident near Winters, CA. Investigators recorded the probable cause as: The pilot's failure to maintain adequate airspeed and altitude during takeoff from a loading truck, which resulted in a collision with the terrain. This summary draws on records from the U.S. National Transportation Safety Board (NTSB) historical archive.
A helicopter descended into ground effect and collided with terrain while attempting takeoff from a loading truck for an aerial application flight.
What happened
The pilot was conducting his 16th aerial application mission of the day when he attempted to launch the helicopter from a loading truck. Prior to the takeoff attempt, the pilot reduced the chemical load from 90 gallons to 70 gallons because the wind conditions had become variable. As the helicopter lifted off, it descended into ground effect, which is the zone where the aircraft normally begins to attain translational lift. The helicopter subsequently collided with the terrain and was destroyed in a post-impact fire.
The investigation
During the investigation, the pilot stated that he was unable to stop the descent despite applying full power. This suggests that the aircraft lacked sufficient performance to climb out of ground effect under the prevailing conditions.
Probable cause
The pilot's failure to maintain adequate airspeed and altitude during takeoff from a loading truck, which resulted in a collision with the terrain.