Flying coach is never fun--or comfortable. And a long flight can quickly begin to feel even longer when the person sitting next to you is spilling over into your seat. According to Robin Urbanski, a spokeswoman for United Airlines, the company received approximately 700 complaints in 2008 from passengers stuck in this predicament. These complaints prompted the airline to implement a new policy in 2009 to help ensure the "comfort and well-being" of all passengers flying United. The airline's new policy targets "passengers who are unable to fit into a single seat in the ticketed cabin ... properly buckle the seatbelt using a single seatbelt extender ... and/or ... put the seat's armrests down when seated."
As stated in this policy for "passengers requiring extra space", individuals who meet this criteria will reaccommodated next to an empty seat. If no empty seats are available, the "customer must either purchase an upgrade to a cabin with available seats ... or change his or her ticket to the next available flight and purchase a second seat in addition to the one already purchased. If a customer meeting any of [these] criteria cannot be accommodated next to an empty seat and chooses not to upgrade or change flights and purchase a ticket for an additional seat, he or she will not be permitted to board the flight." See United Airlines' website for full details.
It's not just United though--policies and/or plans for dealing with heavier passengers are relatively commonplace for US airlines (mainly due to safety concerns for all passengers.) In fact, Southwest Airlines' "customer of size" policy has been in place for over 20 years. More recently, American Airlines was the victim of lots of negative press after a photo (reportedly taken by a flight attendant) showing an extremely obese passenger attempting to fit into a seat was found on an aviation blog. In addition, Air France made headlines earlier this month after changes were made to its policy regarding larger passengers.
We were always advised to travel light, but now that phrase has taken on a whole new meaning for many Americans.