Updated

The crash of a light plane on a remote mountainside in western Maine killed the pilot and three high school students who taking an introductory flight lesson, authorities said.

The three passengers, members of an Air Force Jr. ROTC program, were participating in a summer leadership program that included an introduction to flight, Lewiston High School principal Gus LeBlanc said Friday.

"It's kind of unspeakable at this time," LeBlanc said.

The four-seat Cessna 172 crashed Thursday about an hour after picking up the students at the Bethel airport. The passengers' names were not immediately released.

The pilot, 24-year-old Charlie Weir, was a certified flight instructor with more than 900 hours of flight experience, said Nate Humphrey, president of Auburn-based Twin Cities Air Service, which operated the plane.

The cause of the crash was not immediately known, Humphrey said. The National Transportation Safety Board will investigate.

Recovery operations began Friday to remove the four bodies from the wreckage, which sat in a heavily wooded area near a ravine.

"It's incredibly difficult terrain to get into," said Mark Latti, spokesman for the state Department of Inland Fisheries and Wildlife. "One of the wardens said it's as close as Maine has to a jungle."