WASHINGTON (AP) _ Aviation experts say that if Payne Stewart's Learjet depressurized, those aboard the small plane likely perished quickly. Commercial jet passengers would face a lesser risk.

A loss of pressurization could almost instantly drain safe breathing air out of the relatively small cabin of a 10-seat jet like the Lear 35 carrying Stewart and presumably five others Monday. It crashed in South Dakota, killing all aboard.

A pressure leak would take more time to suck the air out of the bigger cabin in a commercial plane carrying as many as 500 people.

During that time, oxygen masks for passengers would fall from the aircraft ceiling, and the flight crew would have a chance to don pressure masks and make an emergency dive below 10,000 feet _ where the air is safe to breathe.

While the outside air at an airplane's cruising altitude is too thin and cold to support human life, jets are pressurized to fly at that height because they can get better fuel economy and a smoother ride.