Flying over the water at night was mentioned as particularly difficult by the three pilots and three instructors interviewed by Reuters news agency.
While most stressed it was too early to determine a cause of the crash, many cited Kennedy's limited flight time as a handicap no matter what problem may have arisen.
"Low flight time, night time. Everything was stacked against him," said Ernie Carnahan, an instructor with Tradewinds International Flight School in Fort Pierce, Florida. "I would say that he probably got disoriented or vertigo over the ocean at night."
While some have attributed the tragedy to a family "curse", other commentators have questioned Mr Kennedy's decision to fly on a hazy evening in a plane he had owned only since April and on a license obtained just 15 months ago.
But a former US Air Force pilot, who did not wish to be named, said Mr Kennedy may have done the best any pilot could have done in the circumstances.
"We just don't know the full story," said the former C-130 rescue pilot, who added that flying visually at night was difficult. "He could have followed a false horizon down into the sea or up until the plane stalled."
The Aircraft Owners and Pilots Association (AOPA) spokesman Drew Steketee said even private pilots licensed only for visual conditions get some instrument training for emergencies. "I wouldn't call it reckless," Mr Steketee said of Mr Kennedy's flight.Reuse content