Thirteen people, including five civilian and two Nepal Army personnel, were killed onboard the Huey UH-1Y chopper dispatched for a relief operation in Dolakha district. There was no damage to third-party property. The wreckage of the chopper was found after days of intense searching.

The report submitted to Tourism Minister Kripasur Sherpa on Friday said that the pilot’s lack of understanding on the specific and severity of weather condition in Kalinchok mountain range resulted to the crash.

The pilot flew inadvertently into fast-building clouds and up-drafting winds in Kalinchok Mountain, losing situational awareness and control of the aircraft, following which the aircraft hit the terrain at an altitude of 11, 200ft, stated the report.

The nature of the crash was—Controlled Flight into Terrain (CFIT). This means, a state of flight when the pilots have full control of the flight and yet the plane hits terrain.

According to the report, the chopper inadvertently entered instrument meteorological conditions (IMC) from visual flight rules (VFR). VFR are a set of regulations under which a pilot operates an aircraft in weather conditions generally clear enough to allow the pilot to see outside the cockpit to control the aircraft's altitude, navigate, and avoid obstacles.

Flights under the VFR condition are not permitted to enter the IMC unless the aircraft gains height or clear the surrounding terrain and it is the violation of the rules, aviation experts said. “The pilot loses sight of the ground, if he/she subsequently enters into IMC from VFR.”

The report said that while navigating along the vast terrain and adverse weather condition, the chopper hit the vertical granite face of the Kalinchok Mountain. The aircraft first sheared five inch tree trunk with main rotor blade and slammed into the ground at around 2:50pm. Had the chopper been 50ft above its existing flying position, the crash should have been averted, said an official of the Tourism Ministry.

The chopper had landed at Singati at 2:35pm and evacuated five injured civilian from there. There were two US Marine photographers onboard the aircraft.

The video footage showed that besides five injured civilian, another civilian was trying to board flight, but was off loaded. The report, however, has not pointed out overloading factor for the crash. There were 13 people in the 10-seater aircraft.

Initially, the Nepal Army had refuted claims that civilian were also killed onboard. However, DNA tests and investigations by experts from both countries confirmed that five other people on the chopper were local villagers.

The accident investigation board was formed on May 20 and it was carried out under the Aircraft Accident Investigation Procedure Manual of Civil Aviation Authority of Nepal (Caan). “Normally, military aircraft crash is not subject to the civil aviation investigation manual; however, in the context to avoid such disaster in the future, the report has been submitted to the Tourism Ministry and the Caan. The report has recommended 10 interim safety measures to avoid such disaster in the future.