Aeroplanes, or airplanes if you're American, need to maintain a certain speed to allow flight.
Asked by: Lucie Coltman, Loughborough
Technically this is the so-called ‘stall speed’, where air passes over the wings fast enough to sustain altitude, and for small planes this can be less than 50km/h (31mph). But at such low speeds, the aircraft is easily destabilised, and could fail to leave the runway. So for safety and stability at take-off, commercial airliners must achieve substantially higher speeds exceeding around 250km/h (155mph).