In air transport, a change of gauge for a passenger or cargo flight is a change of aircraft while retaining the same flight number. The term is borrowed from the rail transport practice of gauge change. When a feeder flight connects to a flight on a larger aircraft, this is sometimes called a funnel flight.
A Y-type change of gauge is one in which a given flight is transferred into two other flights with different destinations. In this case, there are two flight numbers. For example, flight number 100 may fly Boston-Paris-Athens, while flight number 200 may fly Boston–Paris–Rome, where the Boston–Paris leg is on the same aircraft in both cases.
Some passengers, such as persons with disabilities or who otherwise are not disposed to make a connection, prefer to book on flights without a change of aircraft. However, passengers could incorrectly assume that if they are traveling on a single flight number they will not be required to change planes. Single flight numbers are typically used for an originating domestic to international destination or the return (e.g., San Francisco to Chicago to Paris).
United States
In the United States, change of gauge is standard practice among the major airlines. As of 2001, 6 US airlines (American Airlines, Continental Airlines, Delta Air Lines, Northwest Airlines, US Airways, and United Airlines) had change of gauge flights. Title 14 CFR Part 258, "Disclosure of Change of Gauge Services", requires air carriers to disclose to passengers, traveling on a single flight number, if they will be required to change planes during the flight. Part 258 requires the air carriers to inform the consumer that there is a change of gauge in the itinerary before the reservation is made.