RADAR readings for the plane being piloted by John F Kennedy Jr have revealed it dropped rapidly at the end before disappearing off the screen.

It was also claimed yesterday that he was nervous about his ability as a pilot and undertook his fateful two-leg journey to the Massachusetts coast in his small aircraft only at his wife's insistence.

The rapid descent late in the flight was at a rate of 4700ft per minute when it was 2200ft above the waters off the island of Martha's Vineyard. Officials said the data indicated the Piper Saratoga was flying at this height at 9.40pm and 20 seconds, but four seconds later it had dropped 300ft, then dropped another 300ft in the next five seconds.

The last radar reading for the single engine, six seater plane, was at 9.40pm and 34 seconds, when it was recorded at 1100ft above the sea.

Just hours before the flight, the 38-year-old son of assassinated President John F Kennedy told a friend he was uncomfortable about landing at the airfield on Martha's Vineyard.

The revelation came as Coast Guard officials declared they had finally given up hope of finding Mr Kennedy, his wife, Carolyn Bessette Kennedy, 33, and her sister, Lauren Bessette, 34, alive.

Mr Kennedy and his wife had been due to fly direct to the town of Hyannisport for the wedding of his cousin, Rory, but he agreed to divert to drop off his sister-in-law at Martha's Vineyard, apparently after pressure from his wife.

The New York Post newspaper reported that Mr Kennedy told biographer friend David Heyman he did not want to go to Martha's Vineyard. ''Unfortunately, I have to take my sister-in-law with us. She's going to Martha's Vineyard. My wife insists I take her there. I don't want to do that. I said I'd rather fly straight to Hyannis ... but my wife's insisting.''

Mr Kennedy reportedly added: ''This means I have to land twice. I'm not really that experienced a pilot.'' He had flown solo for only 46 hours before the crash.

Police are working on the assumption the aircraft crashed nose-first into the Atlantic Ocean. It is possible the cause of the crash may never be known.

A specialist ship yesterday carried out a ''search and recovery'' operation as divers prepared for the grisly task of visiting two potential crash sites at a depth of 60 to 80ft.

As the surviving members of the ill-starred Kennedy dynasty were beginning to come to terms with their latest tragedy, the family said in its first statement they were filled with ''unspeakable grief and sadness''.

''We loved him deeply, and his loss leaves an enormous void in all our lives,'' according to the statement released by Senator Edward Kennedy. It said ''John was a shining light in all our lives'' and described his wife, Carolyn, and Lauren, her sister, as exceptional and accomplished young women who reflected the extraordinary qualities of their family.

Irish Prime Minister Bertie Ahern said Irish people around the world were greatly distressed.

''The Kennedys have a long and proud association with Ireland and represent all that is positive and honourable about Irish-American heritage, in particular its noble tradition of service,'' said Mr Ahern. ''Our hearts go out to members of the Kennedy and Bessette families.''

Earlier, US President Bill Clinton led nationwide mourning by giving a personal message of sympathy when he arrived back at the White House after spending the weekend at his official retreat, Camp David.

He said: ''For more than 40 years now, the Kennedy family has inspired Americans to public service, strengthened our faith in the future and moved our nation forward. Through it all, they have suffered much and given more.''

John Macleod Page 17