But if you are bumped involuntarily, the airline may be required to compensate you unless it can get you to your destination within a certain time.

Airlines are required to compensate passengers who are involuntarily bumped when a flight is oversold, depending on the price of the ticket and the length of the delay.

BRIEFLY, a passenger who is bumped involuntarily from a flight has the right to a flight leaving soon on another plane or to cash compensation.

A Northwest Airlines spokesman said that of the 43 million passengers it boarded last year, about 4,500 were involuntarily bumped.

If too few passengers agree to accept the vouchers, the airlines will have to pay cash compensation to those who are involuntarily bumped.

That policy often results in passengers' being bumped from flights involuntarily.

The Transportation Department said that of the 430 million airline passengers last year, 174,639 were bumped involuntarily -less than five one-hundredths of a percent.

His system, besides preventing any passengers from being involuntarily bumped, would save the airlines money.

Thus 1 in every 10,000 passengers is bumped involuntarily.

The number has dropped slightly over the years - in 1991, more than 40,000 people flying the top nine carriers were involuntarily bumped, or 1.01 passengers per 10,000.