WPR09LA057 · Kaman K-1200

With the engine started and at flight idle, the ground crewman/mechanic disconnected the ground power cart from the helicopter's external power unit plug. As the ground crewman/mechanic was walking away from the helicopter, the pilot detected that a gust of wind was lifting the aircraft up off of its right main landing gear. The pilot applied full right cyclic to counter the uplifting condition; however, the wind gust continued lifting the helicopter to the left and nose down until the aircraft came to rest inverted. As the helicopter was rolling over, the main rotor blades impacted a fueling truck and struck the ground crewman/mechanic. There was no postcrash fire. The pilot noted that the winds were generally light and variable at the time of engine start, and estimated that the gust was from the east-southeast at up to 15 knots. He further reported that gusty, unpredictable wind conditions were not uncommon in the area. The closest aviation weather reporting station was 22 miles south east of the accident site and was reporting winds from 030 degrees at 7 knots. According to the Kaman K-1200 flight manual, the maximum right quartering tailwind condition for takeoff and landing is from 17 knots to 25 knots. The winds at the accident site most likely exceeded the maximum wind allowed with reference to the helicopter's prevailing wind envelope, which resulted in the helicopter lifting to the left and rolling over.

Verbatim NTSB analysis and probable cause from the NTSB dataset