With one engine shut down, the airport ahead smothered in fog and his twin-engine aircraft rapidly losing altitude, Michael D. Spear apparently made a simple blunder -- one that cost the Rouse Co. president, his wife and their 20-year-old daughter their lives.
After a year's investigation, the National Transportation Safety Board has ruled that Mr. Spear, an experienced pilot, probably forgot to accelerate the still-operating right engine of his Piper Cheyenne II after the left engine malfunctioned.
The Spear plane was six miles shy of Boston's Logan International Airport when it crashed at 6:33 a.m. Aug. 24, 1990.
The plane hit two cars in a driveway between two homes in Mattapan, Mass., killing the plane's passengers instantly. Both homes burned, but no one on the ground was injured.
Alan Yurman, the NTSB expert who investigated the crash, said yesterday that Mr. Spear's mistake was comparable to failing to accelerate a car headed up a steep grade.
"Instead of applying more gas to it, you don't do anything and can't go up the hill," he said in a telephone interview from his office in Parsippany, N.J.
The pilot should have been able to fly and land the turboprop plane using the right engine alone, he said.
Investigators sifted through control tower tapes, radar and weather records, and data from post-crash examinations of the plane's engines, propellers and other parts.
Then, in June, all of the data was put into a computerized simulator at a Piper facility in Florida, where an experienced pilot sat in a training mock-up of the Cheyenne's cockpit and re-enacted Mr. Spear's final flight.
The re-enactment supported the theory that Mr. Spear forgot to accelerate the plane, Mr. Yurman said. But it could not show why.
The 49-year-old Mr. Spear flew out of Chatham on Cape Cod, where the family has a summer home, about 6 a.m. the day of the crash. The Columbia resident had a reputation as a methodical and enthusiastic pilot.
About 20 miles from Logan, he radioed the control tower that he was having problems with the plane.
On his first approach to the fog-shrouded airport, Mr. Spear reported he was coming in too fast.
Mr. Yurman said the fuel-control device for his left engine had broken, flooding the engine with fuel and causing it to race and belch smoke.
Mr. Spear radioed that he had shut off the left engine. After circling back, he radioed that he couldn't maintain altitude.
A few weeks after the crash, investigators released information suggesting that the crash might have been caused by the pilot's accidentally shutting off the right engine instead of the left when the left engine malfunctioned.
That did not happen, Mr. Yurman said yesterday.
Background noise in the control tower tapes proved that the right engine kept operating at a constant speed until just before the crash, he said.
An examination of the engine turned up no mechanical problems.
The crash killed Mr. Spear, his wife, Judith, 47, and their daughter Jodi, 20. The couple's three other daughters were not aboard.