It is far too early for anyone to come up with a real cause for the accident, but there is some speculation.
One possibility is that some toxic fumes somehow got from the engine to the interior part of the cabin. However, a more likely theory, although unusual, is cabin depressurization.
That would cause all people on board to lose consciousness and the plane to continue flying on auto-pilot.
Several pilots atRDU International Airportsaid the plane crash is unusual no matter what might have happened to cause it.
If the cabin suffered a quick depressurization, all aboard had very little time to react by putting on oxygen masks.
If the cabin depressurized slowly, the question is how can five people suffer hypoxia, oxygen starvation, at the same rate at the same time.
No matter what, pilots say there should have been a warning.
Mike Jackson is a corporate jet pilot. Most smaller planes, no matter the make or model, have similar instruments including gauges that monitor cabin pressure.
"The cabin altitude is here, and the cabin climb or decent rates are right here. Using these, we are able to monitor the cabin pressurization system," said Jackson.
If the cabin did depressurize, either quickly or slowly, the crew should have had a warning.
"We'd see the cabin pressurization drifting off, and we'd see the cabin climb up. Then, the passenger oxygen masks should automatically deploy, and we should have warning lights come on up front," explained Jackson.
How might the crew and passengers have reacted to a loss of oxygen?
"Each person is slightly different in the effects of hypoxia. Some notice spots in front of their eyes. Some start feeling euphoric or very happy and easygoing. Some people just simply fall asleep," said Jackson.
TheNational Transportation Safety Boardis investigating the accident. Smaller planes do not normally have black boxes or flight recorders.
Stewart was one of the most recognizable players in golf because of his knickers, a tam-o'-shanter hat and a fiery spirit.
Just a few months ago, Stewart won his secondU.S. Open Championshipin Pinehurst.
Stewart came to Pinehurst early and spent time in the village talking with residents and signing autographs. In the Pinhurst clubhouse, a section of the hallway is devoted to Stewart's breathtaking victory.
"He wandered around the village and made himself available to all the local people. He couldn't have been friendlier to all the staff members at the restaurants and the bartenders at the Pinecrest," said Tom Stewart.
Stewart's interaction with the Pinehurst community made him a sentimental favorite among the locals.
Bobby Clampett, a CBS golf analyst and player who lives in Cary, is just one of the people feeling great sorrow.
"We're all in absolute shock. Nothing like this has ever happened to any of us before on the tour. We're a pretty close family out there. I've known Payne since college days, and it's just unbelievable," said Clampett.
Clampett competed against Payne in college and on the PGA Tour. Their families spent time together at events, and their friendship through faith developed over the last two years.
"Payne made some major changes and decisions in his life just recently. As a result of that, when he won the U.S. Open, he was wearing a WWJD bracelet around his wrist that his son had given to him," said Clampett.
Stewart was outspoken and liked by his peers and fans.
"He was a man who put his family first. He put others ahead of himself. He dedicated his life to those and to his game and to compete at a very high level. He was a man who had a great heart for giving it 110 percent all the time," said Clampett.
Stewart won two U.S. Open Championships and a PGA Championship among his 11 tour wins. He also won seven other times outside the United States. andJeff Gravley