The crash of a United States Marines helicopter in Nepal in May that killed 13 people during earthquake rescue operations was most likely caused by the crew’s decision to fly the most direct route to Kathmandu, the capital, the Marines said Saturday.

The UH-1 Huey helicopter took the shorter route from a village east of the capital over unfamiliar terrain “due to a real or perceived urgency” in the condition of the injured civilians, according to a statement by the Third Marine Expeditionary Force in Okinawa, Japan.

The investigation found that it was likely that the aircraft “was enveloped by rapidly developing clouds or lifted into a cloud by rising air currents.” At that point, the investigators said they believed, the crew lost sight of the ground, leading to the crash.

The aircraft had been on a relief mission after a magnitude 7.8 earthquake hit Nepal on April 25, killing more than 8,000 people. The helicopter crashed on May 12 after picking up five civilians injured during a second, magnitude 7.3 earthquake that struck the country that day.

Pilots who were flying in earthquake-affected areas in May described a landscape rife with dangers: active landslides, volatile weather and steep mountainous ridges. The terrain and weather were so treacherous that it took nearly three days to find the wreckage of the helicopter, at about 11,000 feet and eight miles north of Charikot, an area hard hit by the second earthquake. Teams were prevented from immediately recovering the bodies by raging thunderstorms and below-freezing temperatures. Six American Marines, two Nepalese Army officials, and five civilians were on board the helicopter.

Brig. Gen. Sudheer Shrestha, who led a team from the Nepalese Army that was involved in the investigation, said that the findings would most likely have “legal implications,” and could help to determine who would compensate the families of the deceased.

“The Americans visited the families of the Nepalese officers” and the civilians, General Shrestha said in a telephone interview, “and they’re very much aware that they’re not from a rich background; they have a heartfelt feeling for them.”

At the same time, compensation to the families was tricky because any action taken by the Marines could set a precedent for future incidents, he said.

The United States Marines were not immediately reachable for comment.

- New York Times