While the cause of the crash could take months to determine, John F. Kennedy Jr. was flying into Martha's Vineyard under difficult circumstances that would have challenged even the most experienced pilots.

Kennedy, who earned his pilot's licence last year, was qualified for visual navigation only. He wasn't rated to use instruments that help pilots navigate in overcast and darkened skies.

Arthur Marx, a flying instructor at Martha's Vineyard Airport, told Newsworld he'd flown with Kennedy before, though not in the new airplane, a Piper Saratoga PA 32. "I have no idea how good he was in that plane."

Piper Saratoga PA 32

Marx told Newsworld that the weather conditions that night were considered "marginal VFR." (VFR stands for Visual Flight Rules.)

That means visibility was six to eight kilometres, which some pilots consider to be safe. Others say those conditions are more difficult in the dark, and the weather over that part of the Atlantic Ocean is unpredictable.

Marx says he would have recommended that a pilot fly that night only if "reasonably competent on the instruments."

Kennedy had also been flying with an injured foot that he broke in a paragliding accident.

One week ago Kennedy flew into Toronto in his own plane accompanied by a co-pilot who was also a flight instructor.

Magna International executive Keith Stein told CBC News that Kennedy had said he was flying with a co-pilot because his foot made it difficult to operate the pedals.

After meeting with Belinda Stronach, daughter of Magna founder Frank Stronach, Kennedy returned to the airport with Stein, but didn't leave right away.

"He asked me what time it got dark here in Toronto. He was interested in flying at night for some reason," Stein said. "I think he mentioned that it was either easier or he preferred flying at night."

Stein said Kennedy offered to fly a writer who had set up the Toronto meeting back to New York. But Stein persuaded the woman to take a commercial flight back.

Another pilot who made a similar trip from New Jersey to Martha's Vineyard last Friday night said he was able to land at Martha's Vineyard only by using instruments to land.

New York Post columnist Allen Salkin told Newsworld's Ben Chin he believes Kennedy didn't have enough experience to fly in marginal weather conditions. "It shows a sort of fatal flaw in the Kennedy character."

A USA Today reporter, who interviewed Kennedy a couple of months ago, told Newsworld he was excited about his new plane and revealed: "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."

Kennedy received his pilot's licence 15 months ago, and bought a used Piper Saratoga II HP airplane in April.