Debris may provide clues to what went wrong
By Joanna Weiss, Globe Staff, 07/19/99
A wheel. A headrest. A piece of support. As the weekend wore on, the different pieces of airplane that washed ashore on Martha's Vineyard were the sole physical clues to the fate of John F. Kennedy Jr.'s flight.
But specialists in airplane crashes said those bits of debris, and the radar signals that tracked Kennedy's plane just before it disappeared Friday night, are enough to confirm a much-feared fact: that a plane could not have survived such a crash intact.
''If you're finding the airplane in parts, that means it has come apart,'' said Arthur Alan Wolk, a Philadelphia pilot and lawyer who specializes in air crash cases.
Kennedy's plane followed a familiar trajectory as it fell, Wolk said - so common that air crash investigators have given it the macabre name ''graveyard spiral.''
It begins, Wolk said, when one wing dips and the plane no longer generates upward lift. The nose points downward as the plane begins to plunge at an ever-increasing speed.
To escape such a catastrophic dive, Wolk added, a pilot must try to level the wings, reduce speed, and lift the nose back above the horizon.
But Kennedy, who had already started his descent toward Martha's Vineyard, had less than 30 seconds, according to Wolk's calculations of radar records of the doomed flight, to do all this before he hit the water - not enough time to pull out of a steep dive.
His plane would have been traveling at least 4,500 feet per minute when it crashed, Wolk said.
''It's almost like landing on pavement at that point,'' said Len Carroll, operations manager at Wiggins Airport in Norwood.
Finding more debris or any signs of Kennedy, his wife, and sister-in law might take some time, Carroll said. In similar crashes off the Martha's Vineyard coast, Carroll said, locating wreckages has sometimes taken weeks.
Tides and currents can carry debris far from a crash site, he said. And the depth of the water - 25 feet to 100 feet - where Kennedy's plane is believed to have plunged makes a search more difficult. From above the water's surface, it is hard to see objects that have sunk below 10 feet.
Federal investigators cautioned yesterday that the search could take months and that the cause of the crash might never be determined.
But that didn't stop amateur pilots from speculating on what went wrong.
Intense discussion has focused on Kennedy's relative inexperience in the cockpit, the difficult visibility on a hazy, moonless night, and Kennedy's recent upgrade to a more powerful plane than the one he had used for flight training.
But Wolk believes the facts, so far, suggest that airplane malfunction was as likely a potential cause of the crash as pilot error.
A sudden change in altitude after a seemingly normal flight could indicate, Wolk said, one of several mechanical errors: a malfunction of the autopilot, the ''artificial horizon'' that feeds information to the autopilot, or the vacuum pumps that drive the plane's gyroscopic information.
''All of these small planes have a long history of malfunction of various components,'' Wolk said.
But Carroll said physical malfunctions are far less common than pilot error.
''Mechanical things don't happen a lot,'' he said. ''Most of it's something a pilot does.''