The crash of a Piper Cherokee airplane in East Honolulu last year, which killed a Honolulu veterinarian and his 20-year-old son, likely occurred because the pilot was qualified only for visual navigation but was flying in weather that demanded instruments, the National Transportation Safety Board has found.

However, in a rare mitigating statement, the NTSB also noted that an air traffic controller’s failure to issue a safety alert contributed to the accident.

Sue Sylvester-Palumbo, widow of Dr. Nicholas Palumbo, said she remains disturbed by the circumstances surrounding the crash but is "pleased" that the probable-cause report acknowledged the air traffic controller’s partial culpability.

"It’s usually always ‘pilot error’ in these types of reports," she said. "I always felt there were questions about how things were handled by the tower. He was never told to climb. If he had been, he could have avoided that ridge. They basically watched him fly into the mountain."

On Jan. 10, 2010, Palumbo, co-owner of the Cat Clinic, and his son Tim, 20, were on a flight to Hono-lulu from Lanai when their plane crashed into the eastern face of a ridge near Lanipo Trail at an elevation of about 1,950 feet. It took rescue crews roughly three hours to locate the wreckage under heavy clouds and rain.

According to the NTSB report, issued Friday, Palumbo was following a standard flight path that involved flying over the Waialae Golf Course and following the H-1 freeway.

The report cited communication between Palumbo and an air traffic controller that indicated Palumbo may have lost his orientation along the route.

At 1:39 p.m., Palumbo reported that he was next to Koko Head and was directed to descend at his discretion after passing Koko Head. The controller, aware he was a "non-instrument-rated pilot," said she assumed he was trying to avoid clouds.

Three minutes later, Palumbo said he was "in the rain and proceeding to Punchbowl." He followed with a report that he was at Punchbowl at an altitude of 1,900 feet and preparing to land.

The controller told Palumbo that he was actually heading toward a mountain in the opposite direction. She told him to make either a left or right turn to the south. Palumbo did not respond.

According to the NTSB, radar data reviewed during the investigation showed that Palumbo’s plane was already off track when he reported that he was next to Koko Head.

The controller told investigators that her first indication that Palumbo was lost was when he reported being over Punchbowl but was actually far off. She said that at the time of the crash she believed he was in Aina Haina Valley and had enough room to turn around.

The NTSB stated that while responsibility for navigation rests with the pilot, controllers are directed to issue safety alerts if in their judgment the aircraft is in "unsafe proximity to terrains, obstructions or other aircraft."

The NTSB investigation determined that the controller had sufficient information to determine that a low-altitude alert was necessary.

"When the controller recognized that there was a problem with the airplane, she concentrated on correcting his lateral track rather than helping him immediately climb to a safe altitude," the report said.

Sylvester-Palumbo said she remains grateful to the rescue workers who risked their lives to find and recover her husband and son a year ago tomorrow.