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Thursday, July 22, 1999 Published at 15:46 GMT 16:46 UK

World: Americas

Investigating the Kennedy crash

Search: Investigators need all vital parts of the aircraft

The investigation into how John F Kennedy Jnr, his wife and her sister died in the Martha's Vineyard air crash will take up to nine months to complete, say accident investigators.

Kennedy Tragedy
The inquiry is being led by the US's National Transportation Safety Board, the federal agency which reports on more than 2,000 individual incidents across the USA every year.

An accident investigation often begins even before wreckage of an aircraft is discovered.

In the case of the Kennedy crash, experts have already been examining radar records of the plane's final moments.

Clues in wreckage

Once the remains of an aircraft are discovered, the priority is to recover as much as possible, including instrumentation panels, fuselage and fuel tanks. These could offer possible clues to an explosion.

[ image: Debris: Spread over a wide area]
Debris: Spread over a wide area
Only larger aircraft and those used for commercial purposes carry cockpit voice and flight data recorders, designed to remain intact in even the worst accidents.

The NTSB investigators began their work by taking all recovered wreckage from the seabed to the Otis air force base, near Cape Cod, Massachusetts.

There it is being pieced together to try and establish if mechanical failure was responsible for the deaths.

During the Lockerbie investigation, teams put together almost the entire aircraft to establish how the bomb ripped the Pan Am passenger jet apart.

[ image: Computers recreated TWA disaster]
Computers recreated TWA disaster
A reconstruction of an aircraft, when matched with radar information can help investigators produce a computer model of a flight's final moments.

Investigators used this technique to try and pin down what happened to TWA flight 800 which exploded shortly after take-off from New York three years ago.

One of the most difficult tasks facing a team at this stage of the investigation is recovering the wreckage.

The Kennedy plane debris spread more than 40 yards (36 metres) from the main crash site because of the speed of the impact.

This caused additional problems for divers who have had to work in limited visibility to try and recover the remains.

Human error?

While aircraft experts examine the history of the aircraft, its airworthiness prior to the accident and its flying record, other members of the team will look into the pilot's own background and whether Mr Kennedy could have been responsible for the accident himself.

[ image: Recovered: Vital instruments been taken to experts]
Recovered: Vital instruments been taken to experts
According to a preliminary analysis of the radar records at the timeof the accident, NTSB officials say that the Kennedy plane made a series of rapid turns and changes in altitude during its final approach to the Martha's Vineyard airport.

At one point the aircraft was diving at up to 1,500 metres a minute.

Investigators are already actively examining whether this means that Mr Kennedy, who had less than 100 flight hours under his belt, had lost control of the aircraft due to a phenomenon known as "spatial disorientation" which can affect inexperienced pilots.

During spatial disorientation, a pilot loses the ability to determine the true position of the body relative to its surroundings as the inner ear's balancing mechanisms become confused.

The phenomenon can also affect underwater divers.

'Graveyard spin'

One of the worst forms of spatial disorientation is the "graveyard spin".

[ image: Human error: Experts believe pilot may have lost control]
Human error: Experts believe pilot may have lost control
Inexperienced pilots sometimes believe that the nose of the aircraft drops during a rapid deceleration.

When the pilot attempts to correct this illusion by pulling up the nose, the plane can stall and fall into a spin.

If the pilot succeeds in righting the plane, they may sometimes then start to believe that the aircraft is now spinning in the opposite direction.

The pilot reacts quickly by reverting back to the original position, putting the plane back into the spin, this time with catastrophic results.

Speaking at a NTSB news conference hours after divers found the wreckage, Ernie Carnahan, a flight instructor, said this was the most likely scenario.

"He may have lost his instrument lights," said Mr Carnahan.

"We may never know, but the bottom line is, he lost control."

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