Last Thursday morning John F. Kennedy Jr. experienced the simplest of pleasures: he got his blasted cast off. To say his broken ankle had crimped his style would be an understatement. Here was an avid stroller of the sidewalks of New York hobbling on crutches, a daring rollerblader unable to squeeze on his skate.

But the best part of getting rid of the cast, he told acquaintances, was that he could at last pilot solo again. Since breaking his ankle in a paraglider crash three weeks earlier, Kennedy had felt the need to fly with a copilot. Friday's flight, he told acquaintances with exhilaration, would be his first time alone at the controls since the accident.

It is only now that the celebratory moment of shedding a cast seems cruelly fateful.

If only Kennedy had waited until Monday to see his orthopedist, he likely would have taken along a copilot, if grudgingly, and perhaps he, his wife, Carolyn Bessette Kennedy, and his sister-in-law, Lauren Bessette, might be alive today. This is based on one of the prime theories of the crash; that Kennedy -- a relatively green pilot not licensed for instrument landings -- lost control of his plane in the black haze around Martha's Vineyard. An experienced copilot perhaps could have landed safely, relying on instruments.

The story of Kennedy's last 36 hours resonates not only with taunting what-ifs but also with telling elements of the persona he fashioned for himself: a glamorous, almost royal celebrity who embraced commonness; an expert in the eyes of friends on the meaning of life, who had uncanny intimacy with the meaning of death. The death theme surfaced at the oddest moments, even when he was an obscure actor in 1985, playing one of a pair of young, Irish lovers whose drowned bodies are fished from a lake.

Among his last written words -- an e-mail sent at 4:05 p.m. Friday -- was a remarkably uplifting message to a friend, John Perry Barlow, who just had buried his mother after being at her bedside for her final days. Barlow eerily discovered the message late Saturday, well after Kennedy himself was dead. It was not just a condolence, but also a sort of congratulations, Barlow said.

"He understood what it was to be able to be with one's mother as she's dying, to be right there with her," said Barlow, a former lyricist for the Grateful Dead. "I think he was in part congratulating me for being in his club."

As the National Transportation Safety Board investigates the crash of Kennedy's Piper Saratoga 7 1/2 miles off Martha's Vineyard, probers say they will examine his physical health and his state of mind, even the most extraneous events in his and his plane's final days -- anything that might have contributed to the tragedy.

One place to start is early Thursday at Lenox Hill Hospital on Manhattan's Park Avenue, with the seemingly unremarkable removal of Kennedy's cast. He emerged on crutches, his ankle still too tender to bear his full weight, and went straight to the 41st floor of the midtown office tower where he edited George magazine, the glossy monthly that treated politics as entertainment.

Surprising those familiar with his celebrity, Kennedy had become a hands-on editor since founding George in 1995. Friends who, like him, traveled every summer weekend to Martha's Vineyard were struck that, unlike them, he rarely left on Thursday afternoons, but worked well into the night and a good chunk of Friday reading copy, attending meetings and, more recently, courting investors.

On Thursday evening, he was picked up at George by a car service and taken to Yankee Stadium, where he was a guest in the field-side box of the Yankees' principal owner, George Steinbrenner. Kennedy, an ardent baseball fan, took along one of his closest friends, Gary Ginsberg, a lawyer who now works for Rupert Murdoch.

Steinbrenner, a friend of Sen. Edward M. Kennedy (D-Mass.), said today that he first hosted the younger Kennedy about a year ago, and was stunned to receive soon afterward a two-page letter "thanking me for the courtesy of taking care of him at the ballgame."

Although Steinbrenner often offered his skybox, Kennedy always demurred. "He wanted to sit downstairs. He liked being close to where the action was," Steinbrenner said.

Friday seemed to be unfolding as a routine day for editor-in-chief Kennedy. He met with the magazine's publisher, Hachette Filipacchi Magazines, to talk about obtaining further financing. With George losing advertising and circulation, there had been rumors Hachette might pull the plug, and Kennedy had been courting possible investors. The previous weekend, he had flown his plane to Toronto -- with a copilot -- to meet potential partners. After Friday's meeting, a George staffer said, Kennedy "was really happy about the negotiations" and "was in really great spirits. He was feeling fantastic."

Also on Friday, Kennedy went to lunch with a group of the magazine's editors, attended an afternoon staff meeting and mentioned with satisfaction to a colleague that the upcoming issue of George had generated considerable media "buzz" with its article on Rep. Mary Bono (R-Calif.). (The article is accompanied by a photograph of the congresswoman and widow of Sonny Bono as a scantily clad, strange-looking model.)

Contrary to reports that Kennedy had planned to leave the office early Friday, but was delayed by his sister-in-law, Lauren Bessette, who had to attend a late meeting at her investment banking firm, sources close to Kennedy said he always planned to leave at 6:30 p.m. Bessette, a principal at Morgan Stanley here, met him at George at that hour, and the two left at 6:45 p.m. for Essex County Airport in Fairfield, N.J., the sources said. Given the clogged state of New York bridges and tunnels at that hour, they did not reach the airport until almost 8 p.m. Carolyn Bessette Kennedy arrived there by car service several minutes later.

Aware of his status as a beginning pilot, licensed just over a year ago, Kennedy kept his plane at the small airfield tucked in the suburbs of northern New Jersey rather than at Teterboro Airport, a much larger general aviation facility just across the Hudson River from Manhattan. A pilot friend said Kennedy considered Teterboro too close to the complex air traffic patterns of Newark and LaGuardia airports.

Kennedy was a major flying enthusiast, accompanied almost always by his beloved, rare-breed dog Friday. He flew every weekend, invited friends to take to the skies with him and planned to buy ever bigger and more powerful planes. He told a friend, who owned a small jet, that he hoped one day to own one himself. Three weeks ago, just after Kennedy crashed his paraglider, Barlow became fearful that Kennedy was becoming too heady about his flying, and warned him to view the accident as a warning.

"You know just enough to be dangerous," Barlow, 51, recalled telling his younger friend. "You have confidence in the air, which could harm you. . . . You're going to find yourself flying in instrument conditions because you think you can."

The sun was just beginning to set as Kennedy, cast-free but limping badly, took his red and white Piper Saratoga through its preflight preparations last Friday. Kyle Bailey, 25, a pilot with more than a decade of flying experience who also keeps his plane at Essex County Airport and who frequently flies the same route as Kennedy -- Fairfield to the Vineyard -- took special note of Kennedy that night because Bailey had just decided against making the flight.

Bailey said he feared the combination of darkness and haze could be treacherous, causing him to lose sight of the horizon, lose his bearings, maybe even lose control of his plane. Visibility was four to five miles in Fairfield due to haze, near the margin for flying by visual rules, as opposed to instruments.

Bailey was not the only one who noticed Kennedy and his party. A carload of teenage girls cruised by and screeched to a halt just outside the airplane parking area, the ubiquitous JFK gawkers. One ran up to Bailey, squealing: "Is that John Kennedy?" When Bailey said that it was, the girls placed a love note under a rock beside the white convertible Kennedy left in the parking lot.

By then, Kennedy, his wife and sister-in-law were airbound. The Federal Aviation Administration tower in Fairfield cleared him for takeoff minutes after sunset, at 8:38 p.m., and he was flying smoothly out of northern New Jersey airspace. The plane had checked out 18 days earlier in its annual inspection as being in good condition; its mechanical compass had been adjusted only three days earlier.

The plane climbed to 5,600 feet, flying east along the southern Connecticut coast, reaching Westerly, R.I., at 9:26 p.m., when Kennedy steered it out over the Atlantic, en route to the Vineyard. He was flying under visual flight rules, or VFR in aviation terms, meaning he was not required to file a flight plan with the FAA and was navigating on his own, rather than by relying on instruments.

The sky over the Vineyard was black and moonless; haze surrounded the island. He was entering the no man's land that Barlow had warned him against, flying in instrument conditions before he was proficient with instruments. Kennedy reportedly had passed a written instrument test, but not the flying test.

Radar tracked the plane at 2,500 feet as it left Westerly. At 9:40 p.m. and 20 seconds, it was tracked at 2,200 feet, having dropped 300 feet in 14 minutes. It dropped 300 more feet in only four seconds, 300 more in the next five and 500 more in the five seconds after that. Then it plunged into the deep.

Staff writers Howard Kurtz, Don Phillips and Paula Span contributed to this report.

CAPTION: Caroline Kennedy Schlossberg, left, and Maria Shriver chat in the yard at Schlossberg's summer home on Long Island at Bridgehampton.

CAPTION: Ethel Kennedy, center, and her son Douglas, right, head for sailboats in Hyannis Port, Mass., with family friends.