The two 27-year-old men who were aboard a helicopter that went down in a hard landing in a North Kona lava field were released from the hospital Wednesday night, representatives of the company that owns the aircraft said today.

On board were an instructor, who suffered a stress fracture to the spine, and his student, who received a small cut to his hand, Mauna Loa Helicopters personnel said.

The National Transportation Safety Board is scheduled to begin its investigation this afternoon, a company representative said.

The copter went down about 3:30 p.m. Wednesday mauka of the Four Seasons Hualalai Resort, Hawaii County Fire Department officials said Wednesday.

The instructor auto-rotated the helicopter down to a hard landing after the aircraft, a Robinson R22 Beta with a Lycoming engine, experienced engine failure, Kailua-Kona fire Capt. Michael Andrade said.