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The U.S. Centers for Disease Control and Prevention reported Monday that 30 percent of adults in the United States are considered obese. Given that statistic, it may come as no surprise that there's a market for selling seatbelt extenders for in-flight use.

But the Federal Aviation Administration has cracked down on those personal extenders, saying last month in a memo to airlines that they should not be used.

A seat belt is required for every passenger on board a flight. Airlines provide extenders, which, along with seat belts, are inspected and maintained under each airline's Continuous Airworthiness Maintenance Program, according to the FAA.

While some seat belt extenders may be labeled FAA-approved, the agency warns they are not inspected and maintained and should not be used.

An Amazon.com search found several options for personal seat belt extenders, some labeled FAA-approved and others purporting to be designed for a specific airline. They can be purchased for as little as $37.

While the crackdown on seat belt extenders is new, the debate over the rules and rights of larger passengers on board flights is not. Many airlines require larger passengers to purchase two seats. For example, the American Airlines web site reads that a passenger may require more than one seat if they are:

- Unable to fit into a single seat in their ticketed cabin and/or

- Unable to properly buckle their seatbelt using a single seatbelt extender (available upon request from a flight attendant) and/or

- Unable to lower both armrests without encroaching upon the adjacent seating space or another customer.

Southwest's Customers of Size policy also requires the purchase of a second seat for passengers who "encroach upon any part of the neighboring seat." However, the airline does provide a refund for the second seat providing the flight was not oversold.