A Beech 19A single-engine airplane that crashed last summer near Kunia, killing all four on board, showed no evidence of a pre-impact mechanical malfunction or catastrophic failure that would have precluded normal operations, the National Transportation Safety Board said in newly released documents.

The “onsite examination” said the aircraft went down in steep mountainous terrain near Pohakea Pass about 50 feet below the ridgeline at 6:52 p.m. July 28.

Aaron Alder told the NTSB he witnessed the crash.

“We saw the plane come over the mountain and it was flying very low, which is the only reason we took note,” Alder said in an email to the board. “It came over the mountain to the Kunia side, I believe, and it was turning over our heads but the turn almost looked like a car ‘drifting’ like it was on ice sliding.”

Alder said after the plane “finally made the turn it started to fly back in the direction it came, it went out of view and we heard the engines still going and then BOOM, silence.”

Evidence indicated the rented Beech, built in 1969, hit densely vegetated terrain at a nearly wings-level attitude. “Extensive aft compression-type crushing and deformation was noted to the engine assembly and forward section of the airframe and cockpit,” the NTSB said.

The bodies of pilot Dean Hutton, 29, and his passengers, Heather Riley, 27, Alexis Aaron, 32, and Gerrit Evensen, 28, were recovered the day after the crash. All were Oahu residents. The aircraft had taken off from Daniel K. Inouye International Airport 15 minutes before crashing.

Examination of the airframe and engine was conducted at the accident site April 17.

“Onsite access to the wreckage was delayed due to terrain conditions and the remoteness of the site,” the NTSB said in the report released Thursday.

According to the board, the plane’s owner, Jahn Mueller, owner of Aircraft Maintenance & Flight School Hawaii, had indicated he did not plan to recover the aircraft.

A relative of Hutton’s previously said the pilot had 170 hours of flying time. The Federal Aviation Administration and NTSB at the time said a probable-cause determination would be forthcoming in 12 to 18 months.

Mueller told The Associated Press the plane had an alternator issue when he had previously rented the same plane to Hutton but that it was fixed by the time of the July 28 crash.

No alcohol or drugs were found in the pilot’s system, according to the NTSB.

A month earlier a Piper PA 28-140, also owned by Mueller, crash-landed in a Mapunapuna stream under a Moanalua Freeway bridge, injuring three people aboard.

Star-Advertiser reporter Allison Schaefers contributed to this report.