Although the subject is a touchy one, airlines are not just being cruel when they make decisions based on a passenger's size. Safety is the top concern for airlines, which are regulated by the Federal Aviation Administration. Passengers who are unable to fasten seat belts or who may block an exit row can be a danger to themselves and other passengers and crew. Additionally, airlines want to ensure that all passengers are as comfortable as possible while flying. If an individual cannot fit comfortably in one seat, he may inconvenience another passenger.
Increasingly airlines are giving boarding agents the authority to insist that obese customers purchase an additional seat. If you believe that you cannot comfortably fit in one seat with the armrest down, then purchasing an additional seat in advance may prevent some of the embarrassment that could result from being called out at the time of your flight.
Find out if the airline you are flying with offers extendable seatbelts. This is not just important for comfort, but for safety as well. Turbulence during flights can be extreme, and being properly belted can prevent you from being ejected from your seat. In addition, ask about upgrading to the first- or business-class section, which offers larger seats. Although these fares are significantly higher, if you are a member of an airline mileage program, you may be able to use your rewards to upgrade.
Inquire about reduced or refundable fares for a second seat. For airlines that require certain passengers to purchase an additional seat, some offer a discount on the second seat, while others will refund your purchase price if the flight isn't full.