Q: Peter, here's a dilemma for you: A woman sits beside me on a Delta Flight. She carries a seatbelt extender and raises the armrest between us so she can fit into her own seat, plus 25 percent of mine. What are my rights at that time and after the flight? Seems to me that if I don't get all of my seat, I should be compensated or she should be moved. I would very much appreciate your thoughts.

–Robert McDonald, Asheville, N.C.

A: Most airlines have some sort of policy—either a formal one or an unwritten one—on how to deal with those who cannot comfortably fit in one seat. But they walk a difficult tightrope on this issue: They must simultaneously try to satisfy thinner customers who may feel they were wronged by not having full access to the seat they paid for and be careful not to offend or humiliate customers who cannot easily fit into a standard seat.

Southwest, JetBlue, and Air France are the only carriers with explicitly written policies. At Southwest, passengers who cannot fit into one seat (determined by whether or not they can lower the armrests) must buy a second one in advance or risk having to pay up after boarding. They can be reimbursed afterward if the flight turns out not to be full. JetBlue requires overweight people to buy a second seat but does not offer refunds. Air France also requires passengers to buy a second seat at 25 percent of the price of the initial ticket. If the person does not buy the extra seat, he or she may be forced to get off the plane.

Most other carriers, such as United, American, and Midwest, have either no policy or an informal policy that puts handling of obese passengers at the discretion of flight staff. Depending on the airline, the situation, and/or how full the plane is, such travelers may be required to move to a different seat, buy a second seat, or get off the plane.

Delta's policy is to "work to accommodate" passengers who cannot easily fit into a single seat. Staff will try to move a heavier person next to an empty seat, if one is available. If not, the passenger may be asked to get off the plane and to buy a second seat on the next available flight.

So to answer your question, your rights as the infringed-upon passenger are to have access to a seat that you can fully occupy, but not to a refund. Next time you find that your neighbor is overflowing into your seat space, talk privately to the flight attendants at boarding to alert them to the situation. Then the burden is on them to re-seat or remove the obese person in a sensitive manner.

Incidentally, most airlines use the armrest standard, not the need for a seatbelt extender, to determine whether or not a person is too large to fit in one seat.