First, Edgartown seasonal resident William O’Connell was forced to write off his plans for a helicopter landing pad at his Chappaquiddick home. Now, Mr. O’Connell has written off a helicopter, too.

He was at the controls of the Bell B206, with three others aboard, which plunged into the ocean on Saturday off Lake Tashmoo.

No one was seriously hurt when the aircraft apparently lost power and crash landed in Vineyard Sound shortly after 2 p.m. But authorities said the chopper, which belonged to Seaport Aviation Inc, of Quincy, would likely be a writeoff, due more to the effects of immersion in salt water than damage from the impact.

Exactly what went wrong is unclear. Holly Baker, speaking for the Federal Aviation Administration (FAA), said no distress call went out from the chopper before it hit the water.

She said it had flown from Norwood and was on approach to land, about six miles from Martha’s Vineyard airport. There had been normal radio contact with the airport only shortly before it went down, at which stage, she said, nothing seemed amiss. It was a bright, clear day.

The crash was witnessed by a large number of people nearby, and a number of pleasure craft in the area quickly rescued those on board: Mr. O’Connell, his brother William O’Connell, also of Quincy, and two passengers, Michelle Mussaw and Melanie Smith, both of Nashua, N.H. There also were two dogs on board.

They were taken to Martha’s Vineyard Hospital but declined any treatment, state police said. Witnesses said the helicopter descended rapidly, but with its rotors still turning, and hit the water about 1,000 yards from shore.

“They seemed pretty shaken up, but no one was injured, I think,” said an eyewitness, Sid Smith, whose boat was second at the scene.

“I saw it happen. It looked like the helicopter was coming down to land on the water. Then I realized it didn’t have any pontoons.

“It touched the water with the rotor still spinning, then rolled to the right. The blades caught the water and flipped the whole thing upside down. But it floated.”

He said others at the scene threw life jackets. Several boats then took the helicopter passengers to shore.

The Coast Guard said yesterday that it received about 15 calls, starting about 2:10 p.m., reporting the crash. They immediately issued a marine broadcast over the radio to alert mariners of the crash to assist if possible.

By the time the Coast Guard vessels arrived from Woods Hole, the drama was over, although they maintained a security zone around the crashed helicopter, until it could be salvaged.

The chopper was later loaded onto a barge and then a flat bed truck and taken to the airport. It arrived Sunday afternoon. Yesterday, FAA investigators were examining the aircraft to establish the exact cause of the accident.

Mr. O’Connell’s helicopter travel has caused him trouble before. Last July the town of Edgartown issued a cease and desist order to prevent him using land he had bought adjacent to his house on Chapaquiddick as a landing area.

The planned heliport was to be on Lot 7 on Sandy Road, which was bought for $287,900 in September 2006.

But helipads were prohibited under an Edgartown zoning bylaw, after a previous dispute with another property owner in the 1980s.

Mr. O’Connell got as far as clear-cutting a 106-foot by 104-foot area.

Ironically, the area he cut was part of an eight-acre subdivision that a group of landholders, including Mr. McConnell, had previously argued was environmentally sensitive when they were attempting to block plans to construct three affordable homes in the area.

This is not Mr. O’Connell’s first accident on the Vineyard. In July 2002 he was involved in a fatal boating accident off Chappaquiddick and was charged with motor boat homicide. He was later placed on probation for six months.