Helicopter Settles in Canyon After Wake Turbulence Encounter and Dump Valve Failure (N2238W)

Accident Narrative

A helicopter pilot reported that during takeoff from a nearby nurse truck, the wind was from the northeast at 5 to 7 mph. He conducted an observation pass across the area to be treated, then began a descending right turn to make a swath run in the opposite direction. The pilot stated he was unaware of a wind shift to the northwest. Subsequently, the helicopter encountered what the pilot thought was wake turbulence from the observation pass. The aircraft began to settle, and the pilot increased the collective in an effort to stop the descent. The pilot said the 'recovery ended in a deep canyon approximately 150 to 200 ft deep.' The emergency trip door solenoid to release the load failed to work. The pilot was only able to sustain a hover for approximately 2 minutes before the aircraft settled on a 30 to 40 degree embankment and slid down 40 ft to trees, tail first.

Mechanical Issues

Reportedly, the dump valve failed to operate due to corrosion from chemicals carried on the previous flight.