It was still light on Friday evening (local time) when Mr Kennedy jnr drove out of Manhattan in his white Hyundai sports car. He reached the Essex County airfield, Fairfield, at around 8 p.m., where he met his wife, Carolyn, and her sister, Lauren.
Along the north-east coast it was a settled, hot evening, with light winds and no hint of storms. However, beyond the bright lights of New York visibility was not good. There was little moonlight and a heat haze hung over the coast.
Mr Kyle Bailey, a fellow pilot who was also planning on making the trip up to Martha's Vineyard in his own plane on Friday, thought better of it. "The weather was very marginal - four to five miles (6.5-8km) visibility, extremely hazy," he said yesterday. Mr Kennedy may also have had his doubts but he decided to risk the trip.
As he prepared to leave for the short flight in his Piper Saratoga II HP to Massachusetts, where he was to attend his cousin Rory's wedding the following morning, he was wearing a T-shirt and white jeans. However, he had broken his ankle in a sports game a few weeks earlier and his foot was still bandaged. Someone who saw him at the airfield said he was carrying a crutch. He limped to his plane. The Saratoga's rudder is foot-controlled.
As he went through his preflight checks, Mr Kennedy did the standard rev-ups in the aircraft parking area. Mr Bailey, standing nearby, thought that was odd. "It just caught my attention, like, `Why is he doing that here?' " He says he wondered at the time if there was "something wrong with the plane".
However, Mr Kennedy was cleared to take off at 8.38 p.m. and took off into the sunset without incident. First, he headed south, before banking to the left and beginning the trip towards the north-east.
Mr Kennedy's flight path took him back over New York and its suburbs, through some of the busiest air space in the US, with commercial aircraft flying in and out of La Guardia, Newark, and the airport named in memory of his father, JFK, on the western end of Long Island. Private planes do not need to fly under civil or military air traffic control. Mr Kennedy did not lodge a flight plan.
Once he got clear of the busy area around the city, he would have been able to increase his altitude as he climbed above Long Island Sound and headed east, keeping out to sea.
"It was very hazy, and it was very dark, and it was very hard to see the horizon," said Mr Michael Bard, a pilot who flew out from the Vineyard airport at 9.15 p.m, as Mr Kennedy must have been beginning to prepare his landing.
"If you're not instrument-rated [able to fly on instruments alone] it could be difficult maintaining the airplane in an upright condition," he said.
Mr Kennedy's licence allowed him to fly single-engine planes, carry passengers and fly at night. However, he was relatively inexperienced and was not qualified to fly in dangerous weather. He had not yet qualified to fly on aircraft instruments alone.
On Friday night, at around 9.30 p.m., somewhere just to the west of Martha's Vineyard, the plane disappeared.
Mr Kennedy bought his Saratoga from a New Jersey businessman, Mr Munir Hussain, in April. The plane was built in June 1995. It is a six-seater with a range of more than 900 miles and a cruising speed of 180 m.p.h. It is equipped with a ground approach warning system and a storm scope, enabling the pilot to get early warning of weather hazards.
Mr Kennedy had been flying for around two years and was what is known as a "low-time" pilot. He earned his pilot's licence just over a year ago, on April 22nd, 1998, but had logged fewer than 200 hours at the controls.
However, Mr Kennedy had a reputation as a cautious pilot. He had gone down to the Piper's manufacturers in Florida this year to learn about his new aircraft. He often took an instructor with him on his regular flights up and down the north-east coast.
In an interview a year ago, he told USA Today that he had got his licence, but that none of his relatives could be persuaded to fly with him. "The only person I've been able to get to go up with me, who looks forward to it as much as I do, is my wife."
AFP adds:
Pilot error, perhaps an "untimely manoeuvre", was probably responsible for the flying accident, a French aircraft accident specialist said yesterday. Pilot and aviation engineer Mr Serge Roche told AFP that the possibility of engine breakdown or fuel running out could be effectively ruled out.
"In both cases the aircraft would have glided and not have smashed into the water," he said, describing the Saratoga Piper as "reliable".