The National Transportation Safety Board investigation found that the helicopter's hydraulic pump had failed due to lack of lubricant, and that even though it had been serviced only 15 days earlier, the pump was severely worn and rusty.

"A metallurgical examination of the hydraulic pump revealed that it had failed due to the wearing away of the splines on the coupling sleeves. ... There was rust on the front retaining rings and bearings, which indicated that there was insufficient grease in the splines to retain it or lubricate the splines," the NTSB report said. It cited as causes of the crash the pilot's failure to follow correct procedures for a landing with hydraulic failure, Heli USA's faulty maintenance, as well as a manufacturing flaw in making part of the hydraulic pump.

The NTSB said that the pilot, who was 5 feet 1 and weighed 108 pounds, should have landed as soon as possible, instead of flying back to her home airfield. She simply wasn't strong enough to control the helicopter for as long as she needed to for the flight, the NTSB said.

"The National Transportation Safety Board determines the probable causes of this accident as follows. The pilot's failure to land as soon as practical. ... Contributing to the accident was the pilot's physical stature and strength," the agency's report said, in part.

Reach Jan TenBruggencate at jant@honoluluadvertiser.com.