SEA LANDINGS A LAST RESORT FOR AIRLINERS.

Byline: Andrew Revkin The New York Times

As investigators continued to study radar traces and other clues to determine what caused Swissair Flight 111 to plunge into the Atlantic on Wednesday, experts in aviation accidents said it was not surprising that no one survived the impact.

Even if the pilot still had control of the wide-body jet and tried to ditch, aviator parlance for setting it down on the sea, chances were slim that it would have held together, several crash investigators and aviation engineers said.

Airline crashes at sea tend to end badly even if the plane is still intact as it hits the water, said Gary Frings, who directs research into the ``crashworthiness'' of airplanes at the Federal Aviation Administration Technical Center, in Atlantic City, N.J. ``Even in the best circumstances, landing on water is very, very risky,'' he said.

In issuing certificates for aircraft like the Swissair MD-11 that crashed, the FAA has in theory deemed that the plane is strong enough to survive a water impact, Frings said. But he emphasized the word ``theory,'' saying that there is no practical way to know what designs will survive or disintegrate in such a crash.

``I crash airplanes for a living,'' Frings said. ``We just did one here two weeks ago. But I wouldn't even begin to try and figure out how you would do that.''

Difficult to predict

Any number of factors - from the size and direction of waves to the rate at which a plane is descending into the water - can in one instance lead to a survivable landing or in another cause the fuselage to ``shatter like an eggshell,'' said Harry Robertson, who has investigated airplane accidents for 40 years and runs the Crash Research Institute, a school for crash investigators in Tempe, Ariz.

Even though the surface of the sea might seem more forgiving than a concrete runway during a crash landing of an airliner, the opposite is often true, he said.

Like a can opener

The corrugated surface of a wind-roiled bay can rip into the fuselage of a jetliner like a can opener, shattering the aluminum sheeting, Robertson said. This is more true of modern jets than older planes, he said. The aluminum alloys used today, he said, are stronger but more brittle than those in older planes, which - being thicker and softer - would tend to bend or dent instead of break as the plane struck the sea.

Also, in jumbo jets like the MD-11, which have large engines slung beneath the wings, the engine cowlings tend to catch in the sea surface and violently tear backward at the wings, contributing to the disintegration of the main body of the plane or causing it to somersault.

If the pilot has some control, he can potentially lessen the risks in a water crash by aiming the plane along the waves instead of nosing into them. But overall, Robertson said, ``As a pilot or passenger, if I had a choice where to make a crash landing, I would never pick water. I'd pick the hardest surface I could find - like even a runway.'' When a fuselage hits a runway, it tends to crush instead of shred, he said.

Chance for survival

In a handful of airliner crashes in water, some passengers or crew have escaped alive, leading safety experts in the airline industry to defend the often-ignored briefings at the beginnings of flights, when attendants or tape recordings note the position of life vests, rafts, and exits.

The most recent crash landing of a wide-body jet in the water occurred on Nov. 24, 1996, when a hijacked Ethiopian Airlines Boeing 767 ran out of fuel and ditched in the sea a few hundred yards from a tourist beach in the Comoro Islands, in the Indian Ocean.

The plane split into three pieces, killing 127 people. But 48 people survived, many of them emerging from the wreckage with only cuts and bruises.

Thus, because there is at least a slight chance of surviving, it is worth listening attentively to the safety briefing, said James Burin, a spokesman for the Flight Safety Foundation, an industry group in Washington that represents airlines, including Swissair, plane manufacturers and insurers.

``It doesn't hurt to look and see where those exits are,'' he said. ``When you're ditching at sea, it's a little late to get out that safety card and read it.''

Learning safety plan

Norman Wiemeyer, one of the investigators of the Trans World Airlines Flight 800 crash for the National Transportation Safety Board, said that by the time an airplane is in the water, it is too late for passengers to start learning.

``In the water, you've got a tremendous amount of turmoil and confusion and stress,'' he said. ``Even if the passengers held a class before they got on board, it probably wouldn't help much.''

He described a helicopter crash in Hawaii that he investigated several years ago. Everyone survived the initial impact unscathed, he said, but several people - including the pilot - drowned because they had not donned life vests.

In the case of Flight 111, Canadian investigators said Friday that it was still not clear if the pilot had control in the last moments as the jet descended toward the Atlantic after dumping spare jet fuel.

But even if he did, with the plane going down in the dark, off a part of the Nova Scotia coast known for tumbling seas, it was highly unlikely that the jet could have been set down intact, Robertson said.

Burin, at the Flight Safety Foundation, said that if Flight 111 went down under the pilot's control, it was clearly as a last resort.

``The only reason you would ditch like that,'' Burin said, ``is because you've lost the ability to fly,'' he said.