N25LBBell 47G-5A · 1972

The pilot reported that he was conducting aerial agricultural operations in a helicopter and that he landed on the bed of the service truck to reload with insecticide and fuel. The pilot further reported that he began to lift off and during the transition to forward flight he pitched the helicopter forward to gain airspeed, but helicopter continued to descend. The pilot reported that he "never gained lift from the ground effect" and subsequently impacted the terrain.

The helicopter sustained substantial damage to the tail boom and fuselage.

The pilot reported there were no preimpact mechanical failures or malfunctions with the airframe or engine that would have precluded normal operation.

FAA Helicopter Flying Handbook Chapter 2 "Aerodynamics" defines "In Ground Effect (IGE)" as the increased efficiency of the rotor system caused by interference of the airflow when near the ground. The air pressure or density is increased, which acts to decrease the downward velocity of air. Ground effect permits relative wind to be more horizontal, lift vector to be more vertical, and induced drag to be reduced. These conditions allow the rotor system to be more efficient. Maximum ground effect is achieved when hovering over smooth hard surfaces. When hovering over surfaces as tall grass, trees, bushes, rough terrain, and water, maximum ground effect is reduced. Rotor efficiency is increased by ground effect to a height of about one rotor diameter (measured from the ground to the rotor disk) for most helicopters.