What is Rule 240 and does it still apply?

Rule 240 refers to the airline requirement to book passengers from a cancelled flight on the next available flight, even if it’s on a competing airline. This rule formally ended with airline deregulation in the late 1970s, but many airlines still honor it to some degree. If the airline agent indicates there are no seats available on the airline’s own flights ask if the airline has a “conditions of carriage” policy, which is the current version of the rule and means that the airline will re-book you on another airline without cost. This will sometimes work if the cancellation is due to something within the airline’s control, but seldom applies to incidents related to weather or strikes.