WASHINGTON (AP) _ The fragmented aircraft parts and human remains being recovered suggest EgyptAir Flight 990 stayed relatively intact until it shattered on impact with the ocean surface, experts said Tuesday.

They noted that searchers had recovered dozens of bodies and large sections of TWA Flight 800 in the hours after it exploded in the air off the coast of Long Island in 1996.

Investigators and aviation experts still don't know what happened this time. But the thought that an intact plane entered a sudden and fatal dive from a cruise altitude of 33,000 feet opened up broad avenues for speculation, including the possibility that something happened to the crew.

``An airplane just doesn't dive out of the air at that altitude unless there's something that happens,'' said Billie Vincent, former security chief for the Federal Aviation Administration.

Like others, he was unwilling to venture a guess until learning more about the circumstances of Sunday's EgyptAir crash off Nantucket, Mass.

The National Transportation Safety Board said the plane was cruising at 33,000 feet when it suddenly descended in a straight line to 16,700 feet _ a drop of 16,300 feet _ within 40 seconds. At the time, the plane had a ground speed of about 600 knots, or about 690 mph.

Jim Hall, the board's chairman, said that after the plane provided that last altitude reading, radar tracked it turning steadily to the right over 37 seconds before disappearing from the scope.

Ed Crawley, head of the aeronautics and astronautics department at Massachusetts Institute of Technology, said that when taking into account both the speed at which the plane was dropping from the sky and the speed it was moving across the ground, the 767 was moving at 744 mph in its dive.

``The data indicate the plane was largely intact and under some sort of aerodynamic control,'' Crawley said.

The fragmented remains show that the fuselage hit the Atlantic Ocean with tremendous force. Merchant Marine students who were the first on the scene said the impact site was strewn with personal effects and parts of the Boeing 767.

On Tuesday, the NTSB told relatives not to expect the recovery of any intact bodies. That would suggest the bulk of the plane stayed together until contact with the ocean surface, experts said.

When TWA Flight 800 exploded in 1996, the plane ripped open at about 13,000 feet, spilling out bodies and breaking into large pieces.

Many of the bodies recovered were damaged but intact, which would occur because a free-falling human being will not go any faster than about 130 mph, due to the balance of gravity and wind resistance.

An airplane, which is designed to be aerodynamic and is powered by jet engines, could achieve a much higher rate of descent.

``If you had an intact airplane diving into the surface, you would tend to get considerably more of a shatter effect than you would if you had a free-falling airplane that exploded at altitude,'' said Bill Hendricks, the former head of major accident investigations for the NTSB.

As to what caused EgyptAir's plummet, two crashes offer possibilities.

In December 1987, a Pacific Southwest Airlines jet plunged to the ground about 175 miles northwest of Los Angeles after a gunman apparently shot the flight crew. All 43 aboard were killed.

An even more bizarre incident occurred in December 1997, when a SilkAir jetliner plunged at supersonic speed into a Sumatran river during a flight from Jakarta to Singapore, killing all 104 aboard.

Investigators still have not determined the cause, but there have been published reports that the pilot of the plane had taken out a life insurance policy worth several million dollars just days before the crash.

Vincent said: ``In either case, you would have a plane that goes in relatively unimpeded because its controls are pointed at the ground.''