Aerospatiale AS350 N188FS accident near Tampa, Florida

Probable cause

The flight instructor's inadvertent throttle reduction below idle, which resulted in a total loss of engine power and subsequent impact with terrain following a power-off autorotation.

NTSB analysis

The flight instructor in the helicopter reported that he directed the pilot receiving instruction to conduct an autorotation with a 180° turn, followed by a power recovery. Abeam the departure end of runway, he moved the throttle lever from the "fly" position to idle. While conducting the maneuver, the pilot overshot the runway and aligned the helicopter with the parallel taxiway. Upon realizing that the helicopter was not in the correct position, the pilots chose to abort the maneuver and perform a go-around. While the pilot continued to fly the helicopter, the instructor inadvertently moved the throttle lever from idle aft toward the "off" position and then forward to the "fly" position. The engine experienced a total loss of power, and the instructor adjusted the throttle to no avail. As the helicopter descended, the pilot requested that the instructor "get on the controls." The instructor took the controls, conducted a power-off autorotation, and landed the helicopter on the taxiway. The helicopter skidded about 180 ft, departed the taxiway onto adjacent grass, and came to rest in a drainage ditch. The instructor reported that there were no preaccident mechanical failures or malfunctions with the helicopter that would have precluded normal operation. The Federal Aviation Administrator inspector who examined the helicopter reported that the left antivibrator mount beam had sustained substantial damage.

Text from the NTSB. Open the NTSB docket for ERA20CA106 for the full record.