Near dawn on Feb. 9, 1982, a Japan Airlines DC-8 on final approach to Tokyo's Haneda Airport suddenly turned nose downward and plunged into Tokyo Bay. Investigators later determined that the plane's captain had pushed his yoke forward on purpose - and that he and his co-pilot had fought each other for control of the plane in its final seconds.
Almost 18 years later, US safety officials say that EgyptAir Flight 990 may have suffered an eerily similar fate. A range of evidence, they say, makes them suspect that a co-pilot's actions may lie behind the aircraft's Atlantic descent.
But this theory is far from proven, experts caution. The rarity of deliberate crashes in the jet-airline age is just one reason that investigators will need more evidence before the case is closed.
"If true, would this represent a trend? No. Would this represent a very odd event? Yes," says Todd Curtis, an aerospace safety analyst and creator of the AirSafe.com traveler information Web site.
In the estimated 100 million-plus airline flights that have taken place around the world since 1980, there have been only a handful of documented cases where investigators concluded that deliberate action on the part of a crew member caused a major aircraft accident.
One was the 1982 JAL crash. The pilot - who survived the incident - was later institutionalized for mental illness. In the wake of the crash, JAL adopted strict procedures for the psychological screening of crew members, which remain in place and are among the most strict such rules of any non-US carrier.
In 1994, a Moroccan airliner mysteriously plummeted to earth after its autopilot was disconnected. Government authorities later said that a cockpit voice recorder showed that the tragedy was caused by the pilot's desire to commit suicide.
More recently, in December 1997, a SilkAir Boeing 737 was cruising easily over Indonesia when it fell out of the sky without warning. The case frustrated investigators at first. The 737's rudder was an initial suspect, as rudder flaws are now thought to have at least played a part in several other 737 disasters - most notably, the 1994 crash of USAir Flight 427 near Pittsburgh.
But Indonesian investigators now believe that the SilkAir plane's pilot crashed the plane deliberately. The plane's horizontal stabilizer was found in a nose-down setting that was set manually from the cockpit, according to the investigator's interim report. And the pilot, Tsu Way Ming, had been disciplined three times and demoted once for flying errors. He was in financial difficulty due to gambling debts.
There are other incidents in which crew members - not pilots - tried to deliberately crash a commercial jet. But even including these, the number at issue is such a minute percentage of total airline flights as to be statistically irrelevant, say experts.
"I'd say it's pretty unusual," says Timothy Forte, a professor of aviation safety at Emory-Riddle University in Daytona Beach, Fla. "You have a better chance of hitting the lottery and then being hit by lightning" than of being a passenger on a flight doomed by its own crew.
Nor is it proved that EgyptAir 990 was downed by its own pilot.
The main piece of evidence pointing toward deliberate sabotage is that one of the plane's pilots, briefly alone in the cockpit, said a prayer in Arabic just before the autopilot was disengaged and the plane went into a dive.
Much of what is puzzling about the crash becomes logical if it was an act of murder-suicide, according to investigators. The autopilot disengagement, the suddenness of the plunge, the fact that one control yoke was pushing down and another up are consistent with a scenario of a struggle for control.
"But it would be a mistake to say this is the smoking gun and now we know what happened. I guess I'd want to hear a whole lot more," says Clint Oster, an aviation expert at Indiana University in Bloomington.
There could be cultural differences in the reading of the evidence, for instance. Egyptian authorities, at time of writing, had yet to be convinced that the prayer was not the normal utterance of a pious Muslim.
The push to find a simple explanation for an aircraft disaster is always strong, says Mr. Oster. But improved technology has made planes safer, and crashes are now often the result of complicated chains of events.
Take TWA Flight 800. It's generally accepted that the 747's fuel tanks exploded. But to this day there is not a theory fully accepted by most experts as to what mechanical flaw caused the explosion in the first place.
(c) Copyright 1999. The Christian Science Publishing Society