Bell 47G-3B-1 N83702 accident near Vinton, Iowa

Probable cause

The pilot's operation of the helicopter at high gross weight and high density altitude while still in ground effect, which reduced the efficiency of the rotor system and the amount of lift produced, which resulted in a collision with terrain. Contributing to the accident was the pilot's decision to continue the flight after the first indication of reduced performance.

NTSB analysis

After reloading the helicopter with agricultural spray product, the pilot flew the helicopter off of the loading truck bed for the aerial application flight. Shortly after takeoff, while operating the helicopter at an altitude of about 10 feet above the ground, the pilot noted a decrease in rotor rpm and made a precautionary landing in tall grass. When he noted no anomalies after the landing, the pilot decided to continue the flight. He took off in the helicopter again and flew for about 100 yards before he again noted a decrease in rotor rpm. The helicopter descended and struck the ground with the tail low, which resulted in substantial damage to the tail rotor and tailboom. An examination of the airframe and engine did not reveal any mechanical malfunctions or failures that would have precluded normal operation. The helicopter was operating above tall grass and crops while still in ground effect, which likely reduced the efficiency of the rotor system and decreased the amount of lift produced as compared to operating over bare ground. In addition, the helicopter was loaded to within 16 pounds of its maximum gross weight and was operating at a density altitude of about 2,800 feet, which likely also contributed to the decreased performance of the helicopter.

Text from the NTSB. Open the NTSB docket for CEN13LA463 for the full record.