Witnesses saw a powered-glider maneuvering near a cliff off of Kauai and heard a loud "pop" before the aircraft plunged into the ocean, according to a preliminary report from the National Transportation Safety Board. 

Pilot instructor Steve Sprague, 48, of Kalaheo and passenger, Ray Foreman, 53, of Vista, Calif. were killed in the crash on May 17. According to the report, the aircraft left Port Allen Airport 50 minutes before the accident occurred. 

At about 10:58 a.m., the aircraft described to be a four-cycle engine, Pegasus Quik 912S manufactured by P&M Aviation Ltd. plummeted into the ocean, about 100 yards off Honopu Beach. 

The Star-Advertiser had reported that ocean tour operator Robert Butler saw the aircraft bank within 60 feet of the cliffs along the Na Pali Coast before he heard a pop similar to the sound of a rifle shot. He then saw the powered-glider fly out of control and fall into the ocean. 

Sprague was the owner of Kauai Aerosports, a company that offers flying lessons on the light sports aircraft.