ust after dusk on Friday, John F. Kennedy Jr., hobbled by a broken foot, limped to the flight line of a small airport in Fairfield, N.J., to inspect his Piper Saratoga HP plane.
Satisfied with the plane's condition, Kennedy eased himself into the left pilot's seat and prepared for the routine 125-mile flight to Martha's Vineyard. His wife, Carolyn Bessette Kennedy, and her older sister, Lauren Bessette, climbed aboard the six-seat plane.
The engine turned. The instruments came to life. Within minutes, the powerful single-engine plane roared down Runway 22 and climbed into the hazy evening sky.
No one has seen it since.
Although his trip to Massachusetts was routine, the series of decisions Kennedy made that night - flying a complex aircraft without a flight plan, choosing not to have his flight instructor accompany him in marginal weather conditions, and piloting an airplane with a foot injury - have grown in significance against the backdrop of what last night became a search and recovery operation underway just off Aquinnah, Mass.
The Piper Saratoga vanished from radar screens after a rapid descent at 9:38 p.m. Friday, about an hour into the flight and about 17 miles from Martha's Vineyard airport. Yesterday, searchers recovered bits of the aircraft's fuselage and interior; on Saturday, they found a wheel strut and a piece of canvas luggage with one of Lauren Bissette's business cards attached.
While Kennedy had not mastered all the plane's equipment, officials hope he was familiar with at least one: the voice recording equipment that had been installed in the Saratoga by its first owner in 1997.
''It was an easy on-off switch,'' said Munir Hussein, its second owner, who sold the plane to Kennedy through a broker in April for $300,000. ''I used it several times and it worked perfectly.''
Investigators say the recorder, which captures the words of a pilot uttered both on the radio and within the cockpit, can shed light on what could have caused the plane to dive 700 feet in 29 seconds and apparently plunge into the Atlantic Ocean just off Aquinnah, known as Gay Head.
The details of what happened in the hour before Kennedy's plane disappeared may not be known until - or unless - it is recovered.
But investigators do know the flight seemed routine until the end, according to the review of radar tapes from a half-dozen Federal Aviation Administration facilities along the south coast of New England.
Kennedy had intended to make a daytime flight Friday, but was delayed when his sister-in-law couldn't leave work early enough, and he hit traffic coming out of New York, the Associated Press quoted a friend as saying. But family friends told the Globe last night that they believed Kennedy had planned to leave when he did.
After takeoff, Kennedy cruised eastward, flying at 5,600 feet, a standard altitude for a plane flying east under visual flight rules, procedures that govern pilots who are qualified only to fly by what they can see.
As he flew through gathering darkness, only a few stars emerged through the haze, and a slim crescent moon glowed.
Two other pilots familiar with Kennedy's experience - fewer than 100 hours of time alone - wondered as his plane lifted off. They knew that Kennedy was learning to fly the Saratoga by instruments alone, but that he wasn't yet qualified to do it on a solo flight.
In fact, Kennedy told a business associate in Canada last Monday that for the time being, he'd rather fly with a copilot because his broken foot made it difficult for him to operate pedals controlling the rudder.
Radar stations along the southern New England coast tracked the plane. But because Kennedy did not file an official flight plan, and had no contact with controllers after leaving New Jersey, no one knew his precise route - or that he was piloting.
Warren Morningstar, a private pilot and spokesman for the Aircraft Owners and Pilots Association, said it was not unusual for a pilot to fly without filing a plan.
Still, Morningstar said, ''a flight plan is really an insurance policy, not an air traffic control document.''
''Would a VFR flight plan have started search and rescue earlier?'' he said. ''Yes, it probably would have.''
But for most of Kennedy's flight, everything went smoothly.
Kennedy cruised east flying at 5,600 - a standard altitude for a plane flying east under visual flight rules.
At 9:39, nearly an hour after it had taken off from New Jersey, Kennedy's plane was about 10 minutes away from the Martha's Vineyard airport when it began a sudden and steady descent. Over the next 29 seconds, the plane dropped 700 feet.
It then disappeared from radar screens.
Investigators said yesterday that the air controllers at the Martha's Vineyard airport did not realize that Kennedy's plane was overdue until sometime Saturday morning.
The controller at Martha's Vineyard airport was scheduled to leave at 10 p.m. Friday, and the airport's runway lights were dimmed. To brighten them, an approaching pilot must tune his or her radio to the tower frequency and click the microphone five times in five seconds, or seven times in seven seconds to reach their maximum wattage.
Until the plane's sudden drop, the radar tapes from the FAA facility used to guide planes in and out of T. F. Green Airport airspace in Rhode Island indicated a normal flight.
''We had a plot on him, we were able to determine which plane was his and he was flying at 5,600 feet,'' said Howard Barte, the controller's union local president in Rhode Island.
''He came within 17 miles west of Martha's Vineyard, and then in the last few minutes he seemed to descend rather steeply for that airplane. The last hit was at 1,800 feet and then we lost contact.
''It was just over the last couple of minutes of the flight that this happened,'' Barte said. ''Maybe in five more minutes he would have contacted the Martha's Vineyard tower and begun his descent, but this rate of descent was not normal.
''When you see something like this, you have to ask: Was there something wrong with the plane, or with the pilot? Because that is all there is.''
Tatsha Robertson, Anne Kornblut, and Tom Coakley of the Globe Staff contributed to this report.