The Coast Guard believes it has located the approximate point, about 7 1/2 miles southwest of Gay Head, Martha's Vineyard, where John F. Kennedy Jr.'s plane plummeted into the sea Friday night. And the sonar-equipped ship scanning the area has found objects on the ocean floor within a few hundred yards of that location "that could be part of the wreckage," authorities said at today's press briefing.

But so far, Rear Adm. Richard Larrabee said, Navy divers from the USS Grasp, making their way 115 feet to the bottom, have found nothing at this site.

Kennedy's plane crashed last Friday night off the coast of Martha's Vineyard and authorities have presumed that he, his wife, Carolyn Bessette Kennedy, and his sister-in-law, Lauren Bessette, are dead.

According to information released by the National Transportation Safety Board today, Kennedy's plane began making an orderly descent about 34 miles from Martha's Vineyard. Over the next five minutes, it dropped from 5,600 feet to 2,300 feet at about 185 mph, which is well within the plane's limits on descent and speed.

About 20 miles from the airport, the eastbound plane made a turn to the right and gained about 300 feet in altitude. It turned left after another minute. It turned right again and 30 seconds later began a "rapid rate of descent," according to safety board chief investigator Robert Pearce.

He said the plunge may have been even faster than indicated by preliminary radar data on Monday, maybe "greater than 5,000 feet per minute."

Those movements are consistent with a "graveyard spiral," in which a pilot becomes disoriented or incapacitated and begins a series of tighter and tighter turns until the plane is beyond control.

However, there is no evidence yet whether that happened or whether a mechanical or structural problem brought the plane down or distracted Kennedy.

Phillips reported from Washington.