The long investigation into the cause of the September 2008 plane crash which took the life of Cape Air pilot and Vineyard Haven resident David D. Willey is over, its findings summarized in two words: “spatial disorientation.”

Spatial disorientation is a condition in which a pilot’s perception of direction does not accord with reality. Typically it occurs when flying into poor weather with low or no visibility. With no visual cues, a pilot can lose the sense of direction, including up and down, due to the effects of centrifugal force on the inner ear. It is a commonly attributed cause of crashes.

Officials of the National Transportation Safety Board (NTSB) could find no fault with either Cape Air’s plane or its pilot which might have caused the crash in which the aircraft plunged into the West Tisbury woods shortly after takeoff from the Martha’s Vineyard airport, just after 8 p.m. on the rainy night of Sept. 26, 2008.

The 10-seat Cessna had been properly maintained, there was no prior indication of mechanical fault, and Mr. Willey’s most recent FAA first class medical certificate had been issued just 10 days before the fatal flight.

But the weather was bad. The NTSB report records that “instrument meteorological conditions prevailed.” There was light rain and mist, and an overcast ceiling at 400 feet. The report says while the winds at ground level were light, a National Weather Service sounding from Chatham noted “a low-level temperature inversion with winds from 135 degrees at 39 knots at 1,300 feet [above] mean sea level.

“The sounding further indicated a greater than 90 per cent chance of severe turbulence below 2,000 feet . . .” the report says.

Against that, however, it says the pilot of another Cape Air Cessna, which took off only about a minute after the Mr. Willey’s plane, “did not report any unusual weather during his initial climb and described the turbulence below 1,000 feet as light.”

The report records that Mr. Willey was cleared for takeoff, to make the short flight to Boston’s Logan airport, a few seconds before 8 p.m. He had no passengers aboard; it was a repositioning flight, undertaken so the plane would be on hand for the first passenger flight the next day.

He was instructed to climb to 4,000 feet and make a right turn.

Airport radar depicted the airplane climbing to an altitude of 400 feet — the height of the cloud ceiling — and accelerating to a ground speed of 120 knots shortly after takeoff.

“The airplane made a slight left turn before entering a right turn which continued until radar contact was lost at an altitude of 700 feet and a ground speed of 160 knots,” the report says.

“The airplane struck the tops of approximately 50-foot-tall trees before impacting in a wooded area in between two houses, about three miles northwest of [Martha’s Vineyard Airport].”

The investigators’ description of the crash scene is detailed. It says the majority of the wreckage was strewn along a 305-foot debris path, oriented roughly toward the northwest.

A postmortem examination indicated Mr. Willey died in the impact.

For all the detail amassed by investigators regarding Mr. Willey’s personnel, medical and pathological history, the tests and research on the wreckage and other factors, the NTSB’s conclusion was brief.

“Analysis of the radar and weather data indicated that, with the flight accelerating and turning just after having entered clouds, the pilot likely experienced spatial disorientation.

“The National Transportation Safety Board determines the probable cause(s) of this accident as follows: A loss of aircraft control due to spatial disorientation.”

The aircraft was not equipped with either a cockpit voice recorder or flight data recorder, so further detail of what happened in those few minutes will never be known.

“Flying in a small plane you don’t have the equipment to record exactly what happened,” said the pilot’s brother in law, Gregory Coogan, yesterday.

“We all know what kind of pilot he was, and I think for that reason we all know something happened in that cockpit, but we’ll never know what that was.

“He was a very experienced pilot. He’d dropped relief supplies in Africa, he’d flown 747 cargo planes to Japan. He had covered the world flying. He loved flying,” Mr. Coogan said.

“And he really enjoyed the Cape Air job, flying back and forth to Boston. It gave him a chance to be home with his children at night, which was not an opportunity he had when he flew long trips, when he was stationed in New York or Chicago or Alaska.”

Mr. Coogan said the family was grateful the investigation had come to a close.

“It’s been almost two years, and while we realize it was necessary, it has made it an emotional time again for the family.

“This is something we all have to get through, and we will.”