Neither engine on Rouse Co. president Michael Spear's twin-engine airplane was operating when it crashed in Boston last Aug. 24, federal officials say.
But the exact cause of the crash in Boston's Mattapan section has not been determined, and the National Transportation Safety Board is continuing its investigation.
The crash killed Spear, 49, his wife Judy, 47, and daughter Jodi, 20, the plane's only occupants.
Shortly before the crash, Spear, who was piloting the Piper Cheyenne II, told air traffic controllers he had shut down the left engine because of problems with it.
Controllers moved Spear ahead of other planes so he could land at Logan International Airport, but he said the plane was going too fast to land, and he began circling to make another approach.
He then was coming in too low and said he would try to climb, but the plane crashed, officials said.
The federal investigators dismantled both engines and propellers and concluded that neither engine was going when the plane crashed.
"The tear-down of the left engine and left propeller substantiated that the pilot had shut the left engine down, as he claimed he had," said Drucella Andersen, a spokeswoman for the safety board.
The board would not say whether Spear inadvertently shut down the right engine or whether a mechanical problem caused it to stop.
Several pilots told The Boston Globe it is not uncommon for a pilot to shut down the wrong engine accidentally. One pilot said the right engine may have been shut down intentionally, if it had a problem, to prevent an explosion on landing.
The Spears were flying from Chatham to Boston so Jodi could get a commercial flight to Japan, where she was planning to study during her junior year.