FOCUS: FLIGHT 990: Did it fall or was it pushed?

The likely causes of EgyptAir's crash last week are multiplying: mechanical failure, suicide, sabotage, a fight in the cockpit, even the JFK curse

It was shortly before 2am last Sunday when EgyptAir flight 990, bound for Cairo from New York's JFK airport, vanished from radar screens. It wasn't long after daylight when the terrible truth was upon us: one more time, there had been a horrifying, violent crash of a commercial jetliner into the Atlantic Ocean. One body had already been found and some pieces of wreckage. Nobody expected there to be survivors.

So much for certainty. Everything else that we have learnt since last Sunday has compounded the mystery of what befell Flight 990. Speculation helps nobody, but the urge to know what happened is irresistible. People who fly want to know. Governments that regulate to improve air safety want to know. Boeing, which made the plane, wants to know. And so, above all, do the victims' families.

We do have some frightening scraps of information. Radar images suggest the plane suffered a near-supersonic plunge from 33,000 feet to 16,700 feet in 37 seconds. Apparently, it then dashed back up to 24,000 feet before starting to dive once more. When it had descended to roughly 10,000 feet, the wide-bodied plane, a Boeing 767, appeared to break apart.

Even that data, from the US Air Force, is not categorical in its accuracy. You might hope that the analysis is not correct, because the picture it paints is so horrible. Just over 30 minutes into its journey, when the 199 passengers and 18 crew would have been settling in for the long haul through the Atlantic night, the plane lurched suddenly into a roller-coaster ride more violent than can be imagined. How much of that ride those on board experienced, before they fell unconcsious or perished, we cannot yet tell.

For now, almost any theory of what caused the crash will do. First, there is the mechanical failure versus sabotage question. US officials have been anxious to stifle any speculation over terrorism. In part, this is due to memories of the investigation into the crash of TWA flight 800 in 1996, when the FBI instantly declared itself convinced that saboteurs were responsible. Today, the ignition of fuel vapours in a near-empty central fuel tank on the TWA plane is considered the most likely cause. In the EgyptAir case, nothing has been found that points to criminal sabotage. But there is no evidence to support a mechanical explanation, either.

No wonder all eyes this weekend are on the two so-called "black boxes" discovered on the ocean bed on Friday night by a robot submarine, dropped to the seabed from the deck of the USS Grapple. The boxes, actually painted orange, may yield volumes of information that will either bring us closer to resolving the mystery or even clear it up entirely. That may be optimistic, however. It is possible that they were badly damaged in the crash and that the information on them has been destroyed.

One of the boxes contains a voice recorder. All sounds from the cockpit, including any alarm sirens that were ringing, what kind of noise the engines were making and, above all, what the pilots were saying to each other, would normally have been taped. The other box is a data recorder. The model installed on this particular plane was capable of recording 55 different items of information. They should reveal details of the performance of the aircraft, from the positions of the flying surfaces on the tail and the wings, to the thrust being delivered by the engines as well as direction, speed and rate of descent or ascent.

The voice recorder, which will have been connected to microphones in the cockpit, might prove especially revealing. We could discover, for example, whether the pilots were conscious during that first dive and whether they were still trying to regain control of the plane. That might explain why the plane started to climb again after its initial plunge. But it is equally possible, aviation experts assert, that the plane brought itself out of that initial dive, without help from the cockpit.

As for sabotage, it seems unlikely that this plane suffered a dramatic explosion of the type that downed TWA 800. We know it still had electrical power for the duration of that first descent, because it was still sending its identifying signals to air-traffic control. A small explosion, however, could have punctured the fuselage and caused a sudden decompression. It is possible that the pilots responded by deliberately putting the plane into a dive but that they subsequently lost control.

Alternative criminal scenarios might include a botched hi-jack involving violence in the cockpit. The pilots could have been killed or controls could have been jogged out of position in a fight. Investigators are also considering the possibility that either one of the pilots or an intruder in the cockpit sent the plane diving in an act of suicide. Suicide is suspected in a 1997 Silk Air crash in Indonesia.

But did this plane simply fail? Could something have dropped from it? Even a small piece of debris separating from an engine could damage the tail. This is the nightmare of Boeing, which has suffered one of the worst weeks in its history. First came this accident. Then, on Monday, came revelations that the company had failed to make public a 1990 report detailing concerns, dating back to 1980, that it had about possible flammable gases in fuel tanks on 747s. On Tuesday, the company announced it was delaying the delivery of four jets because it had discovered problems with so-called drip-shields in the cockpit that stop condensation reaching the electronics. Apparently, they might catch fire. All this at a time when the Seattle- based manufacturer is fast losing ground in the aircraft-order stakes with Airbus.

Under special scrutiny are the reverse thrusters, the part in the engine that sends the jet-blast forward to slow the plane on landing. The only other fatal crash of a 767 from mechanical failure occurred in Thailand in 1991, when one of the thrusters on a Lauda Air 767 were accidentally deployed in mid-flight, sending the plane spiralling to the ground. EgyptAir has confirmed that there were problems with a thruster on the plane that crashed on Sunday, and that it had been deactivated just days before the crash. In what may only be coincidence, Boeing confirmed that this plane came off the assembly line, in 1989, immediately before the Lauda 767. (The two models produced on either side of those two planes went to British Airways.)

The radar data, however, militates against the reverse thruster theory. It shows none of the spiralling seen in the Lauda case. Also, modifications to reversers recommended after the Lauda crash were carried out by EgyptAir.

Also waiting for answers is the city of New York. In just over three years, three jumbo jets from JFK airport, heading east at night over the Atlantic, have crashed, leaving no survivors. First there was TWA 800, then the crash of Swissair flight 111, off Nova Scotia in September 1998, and now this. There has been easy talk of a JFK curse. So far, that is nothing more than superstition. No plane leaving any airport in the United States has ever been brought down by sabotage. Unless, of course, we one day learn that a crime, and not mechanical failure, was indeed the culprit in last Sunday's disaster.