$100 hamburger ("hundred-dollar hamburger") is aviation slang for a general aviation pilot needing an excuse to fly.[1]
A $100 hamburger trip typically involves flying a short distance (less than two hours), eating at an airport restaurant, and flying home. "$100" originally referred to the approximate cost of renting or operating a light general aviation aircraft, such as a Cessna 172, for the time it took to fly round-trip to a nearby airport. However, increasing fuel prices have since caused an increase in hourly operating costs for most airplanes, and a Cessna 172 now costs US$95–130 per Hobbs hour to rent, including fuel.[2]
In Perth, Western Australia, a similar mentality eventuated in the 'Rotto Bun Run'. A group of pilots who had run out of Hot Cross Buns on Good Friday decided to fly to the closest open bakery on Rottnest Island. The run is now an annual charity event.[3]