Airplane accident investigators frequently say any accident is the result of several factors coming together in a deadly combination. Remove any one of them from the sequence and the accident would not occur.
While the cause of Friday's crash that killed John F. Kennedy Jr., his wife and sister-in-law is still under investigation, pilot error is something investigators are closely considering. The plane, with Kennedy at the controls, went into a steep dive in the moments before it crashed off Martha's Vineyard. There are two possible explanations: mechanical problems or pilot error. Based on previous accidents, the latter seems more likely, said a longtime accident investigator who spoke yesterday on condition of anonymity.
If Kennedy was at fault, one crucial element in the sequence of events that led to the accident might have been the pressure on him to make the flight in uncertain weather. Pilots call it ''get-home-itis.''
There were reasons for Kennedy not to make the flight - the weather was questionable, and he and his party were delayed leaving New York City, which resulted in the flight departing three hours later than planned. These are critical factors for a pilot not qualified to use instruments to fly in poor visibility.
But there were even more reasons to make the flight: His cousin Rory was to be married the next day; he had promised that he would drop his sister-in-law Lauren Bessette off on Martha's Vineyard before flying to Barnstable airport; he had spent about $300,000 on the the Piper Saratoga II HP 21/2 months ago and may have been eager to use it; and, quite possibly, as celebrities, Kennedy and his wife found the idea of flying in their own private plane much more attractive than traveling on a commercial flight.
Pilots much more seasoned than Kennedy have succumbed to the pressure to reach their destination.
On June 1, an American Airlines MD-82, which was piloted by Richard Buschmann, American's chief pilot in Chicago for the MD-80, landed in Little Rock, Ark., in a driving thunderstorm, went off the end of the runway at 90 m.p.h. and slammed into a light pier. Buschmann and 10 others were killed.
Among the areas investigators in that crash are examining are Buschmann's decision to land at Little Rock in a thunderstorm. The plane, which was scheduled to spend the overnight in Little Rock, was two hours late leaving Dallas and its crew had spent 131/2 hours flying that day, 30 minutes less than the maximum.
''It is something that comes up in many accident investigations, but we have never made any specific recommendation to deal with this issue,'' said an official with the National Transportation Safety Board.
Norman Komich, a commercial airline pilot who works for Damos Research, a Los Angeles-based aviation consulting firm, said that Kennedy almost certainly realized the margins of safety for his flight were diminished, but probably did not consider it unsafe.
''It was not as safe as daytime flight in good weather, and that is part of the judgment process, but 99.9 percent of the time, it would work and I guarantee you, pilots like him do what he did every day,'' said Komich.
Succumbing to pressure to make the flight is being considered as just one link in the chain that led to the accident. If spatial orientation was a cause of the accident, then, almost certainly, leaving three hours behind schedule was a contributing factor, since safety experts think it is likely that Kennedy could have easily made the flight in daylight.
In 1985, a US Air Force tactical air command report found that command fighter pilots with as much as 6,000 hours of flying time could become disoriented flying at night by simple distractions like changing radio frequencies.