SEATTLE — The crash of a small plane in Washington’s Cascade Mountains last July that killed the pilot and his wife from Marion and sent their teenage step-granddaughter on a harrowing survival trek was caused by the pilot’s decision to fly during bad weather even though he was not trained to fly in the clouds, federal investigators say.

The National Transportation Safety Board’s probable cause report, released Monday, said pilot Leland Bowman had received a weather report the morning of the flight that warned against flying in high terrain if it was obscured by clouds.

Bowman postponed their departure time after the first weather report, the safety agency said.

During the first briefing, Bowman disclosed that he had recently acquired a new computer tablet to help him navigate in bad weather, “but he was still learning how to use it,” the report said.

He also acknowledged that he would not be able to fly using only the Beechcraft plane’s instruments if it became necessary, the report said.

Two hours after the second briefing, Bowman, his wife, Sharon, and 16-year-old Autumn Veatch boarded the plane in Kalispell and headed toward Bellingham, Washington.

When they reached the mountains, the clouds became thicker and Bowman descended, but the plane entered a cloud, the agency said.

“At the time, the other passenger was using the pilot’s tablet to help him navigate the airplane, but she accidentally turned it off,” according to the report, which referred to an interview with Veatch. Soon after, Veatch said she saw trees directly in front of the windshield and Bowman pulled back on the yoke to gain altitude, but it was too late.

Veatch told NBC News there was zero visibility before the crash, and then “it was all trees and then it was fire.”

Bowman and his wife died when the airplane clipped trees and slammed into the mountains near Mazama, Washington, on July 11. Veatch survived the crash and found her way out of the rugged terrain and reached safety days later.

Bowman’s decision to fly into conditions that would force him to use only the plane’s instruments “resulted in his failure to maintain clearance from mountainous terrain,” the NTSB said.

The wreckage was spread along a 130-foot-long slope. The first point of impact was a fir tree that was broken off about 100 feet above the ground, the report said. That impact ripped off part of the plane’s left wing. The rest of the plane continued into the mountain slope and caught fire.

Veatch told authorities that she stayed at the crash site for a day before deciding to hike down. She eventually found a trail and followed it to a trailhead on a highway near the east entrance to North Cascades National Park.

A passing motorist picked her up and drove her to a store where employees called 911. She was hospitalized with minor burns and dehydration before being released the next day.

Veatch said the Bowmans were trapped in the burning plane wreckage. She said she couldn’t get to Sharon Bowman but burned her hand trying to free Leland.

Before she fled, she says she told the Bowmans that “I loved them and that it would be OK.”

No drugs or carbon monoxide were found in tests done on Bowman’s blood, the NTSB said.