Theories abound to explain erratic course of Flight 990

With facts in short supply, speculation includes hijack, failed equipment

November 05, 1999|By NEW YORK TIMES NEWS SERVICE

NEWPORT NAVAL STATION, R.I. -- Now that crash investigators have used radar data to lay out a picture of a Boeing 767 on a wild up-and-down course in the last few minutes of EgyptAir Flight 990, people familiar with the airplane are busy trying to concoct a chain of events that would match the data.

Some talk of pilots whose ability to work the controls was reduced or eliminated by a hijacker or by an accident in the cockpit.

Others think that the autopilot might have mistakenly triggered a dive and that the pilots tried too abruptly to pull out.

Still others theorize that a key part, such as the tail elevator, broke.

A few think the problem is on the other end, with the radar information itself, which they say cannot be correct.

All say that their theories could be just wild conjecture, and that the cause could be something no one has mentioned yet.

Whatever the cause, the radar data, released Wednesday by the National Transportation Safety Board, have added a piece to a puzzle that will be difficult to solve, because most of the pieces are still missing.

Nor did the radar data offer a clue to what touched off the accident in the first place, which could have been anything from mechanical failure to pilot error to a terrorist attack.

In interviews yesterday, a variety of experts described a number of plausible explanations for the last minutes of Flight 990, which plunged sharply, then climbed more than a mile before falling again.

Natural aerodynamic tendencies designed into the airplane could help explain part of the up-and-down, porpoising course, but possibly not all of it; parts breaking off in flight could be part of the explanation.

But the experts said they had very little information to go on that would fill in the blanks. Some of that crucial information, such as the condition of the crew and the condition of the plane, might be on the data recorders that the Navy is trying to recover from the ocean floor.

Tim Forte, a former official of the safety board who is now a safety expert at Embry Riddle Aeronautical University, said the fact that there was no mayday call was "a strong indication of some sort of crew incapacitation."

Several experts said that while there was no evidence for it, an attempted hijacking could have taken control of the flight away from the crew, or created erratic or improper commands from the cockpit to the plane's control systems.

Without pilots at the controls, experts said, the natural tendency of the airplane would be to pull out of a dive if the speed became so great that the lift increased.

Whether that would account for a climb as steep as the one reported by radar analysts is not so clear.

The data show a dive from the assigned altitude of 33,000 feet down to 16,700, at a rate of 24,000 feet per minute, triple the rate recommended by Boeing and about 10 times as fast as the fastest normal descent.

But then the plane rolled to the right, dashed back up to 24,000, and then fell to 10,000 feet, where it took a turn to the left and apparently broke up, two miles above the ocean.

From the point when it descended initially to 16,700 feet, about 37 seconds after the first dive began, the plane's transponder, which reports altitude to ground controllers, quit working.

Altitude data from that point forward came from the U.S. Air Force, which has radars that can estimate the altitude of incoming objects by recording the angle of elevation of the radar when the signal hit the object.

But some investigators are dubious that the plane could have climbed a mile and a half, and suggested that the interpretation of the radar data was wrong.

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