This is the critical fuel threshold at which an aircraft has exactly enough fuel remaining to safely return to its base or reach an alternate airfield, plus standard reserve margins. Reaching this state means the current mission or holding pattern must be aborted immediately. Pilots calculate this number before flight and monitor it constantly to prevent fuel exhaustion.
Heard on the job
We just hit bingo fuel, turning heading zero niner zero for RTB.
Insider tip
Joker fuel is a related term set just above bingo, acting as a warning that the critical bingo limit is approaching.