Oahu veterinarian Nicholas Palumbo was off course and not where he thought he was when his single-engine airplane slammed into the side of the Koolau mountain range, according to a preliminary report of the National Transportation Safety Board.

Palumbo, 81, and his son Timothy, 20, died in the Jan. 10 crash. They were returning from a trip to Lanai where the elder Palumbo operated a veterinary clinic.

Six minutes before the crash, when Palumbo reported he was at Koko Head, he was actually about five miles east-southeast off his projected course to Honolulu Airport, according to recorded radio communications and radar data.

When he later reported that he was at the Waialae Country Club, he was actually 2.5 miles east of the golf course, about a mile offshore.

One minute before the crash, Palumbo reported he was at Punchbowl heading toward the airport.

The airport controller told him he was actually heading into the mountain in Aina Haina toward the other side of the island. The controller also instructed him to turn around and head due south. That was the last communication between Palumbo and the airport control tower.

Palumbo's plane crashed into a steep face of a ridge near the Lanipo Trail above Maunalani Heights.

The direct route from Lanai to Honolulu is 300 degrees. Palumbo's plane traveled along a 330-degree track from Lanai, according to recorded radar data.

Numerous eyewitnesses reported the plane crashed in heavy cloud cover, which made visibility poor.