A Summit Air Let L-410UVP-E20 Turbolet impacted a Manang Air Eurocopter AS 350B3e helicopter (9N-ALC) during a takeoff attempt at Lukla-Tenzing-Hillary Airport in Nepal. The aircraft and helicopter were destroyed. One helicopter (Shree Airlines Eurocopter AS 350, 9N-ALK) sustained minor damage. The copilot of the Summit Air plane sustained fatal injuries. Two persons on the ground at the helipad also died in the accident. The L-410 was repositioning to Ramechhap after flying passengers and cargo to Lukla. The captain taxied the aircraft to threshold of runway 24 and handed over control to the co-pilot. Within 3 seconds of the takeoff roll the aircraft veered to the right and exited the runway, travelling about 43 ft across the grassy part on right side of runway 24, before striking the airport inner perimeter fence. It then continued to skid for about 43 ft, and hit two persons before it crashed into the upper helipad. It struck the turning rotor blades of 9N-ALC. The moving rotors cut through the cockpit and the helicopter toppled onto the lower helipad 6 ft below. The left-hand wing of the aircraft broke the skid of another helicopter, 9N-ALK, and came to a halt with 9N-ALC beneath its right-hand main wheel assembly Lukla Airport is located on a mountain at an elevation of 9334 feet (2845 m). The runway is 1729 ft long (527 m) with an 11.7% gradient. Takeoffs must be performed from the downsloping runway 24. The helipad is located to the right of the runway, about 100 meters past the threshold. Probable Cause The commission concluded that the probable cause of the accident was aircraft’s veering towards right during initial take-off roll as a result of asymmetric power due to abrupt shifting of right power lever rearwards and failure to abort the takeoff by crew. There were not enough evidences to determine the exact reason for abrupt shifting of the power lever. Contributing Factors 1. Failure of the PF(being a less experienced co-pilot) to immediately assess and act upon the abrupt shifting of the right power lever resulted in aircraft veering to the right causing certain time lapse for PIC to take controls in order to initiate correction. 2. PIC’s attempted corrections of adding power could not correct the veering. Subsequently, application of brakes resulted in asymmetric braking due to the position of the pedals, and further contributed veering towards right.