Once the engines are confirmed to be stable, the pilots then either press the TO/GA switch, causing the thrust levers to automatically advance themselves to the appropriate power setting (on Boeings),[1] or manually advance the thrust levers to the TO/GA detent (on Airbuses).[2][3] (In Airbus aircraft, if de-rated takeoff power is desired, the thrust levers are instead advanced to the FLX/MCT detent.) In all cases, the engine speeds then increase to provide the computed takeoff power. Flight management computers on modern aircraft determine the amount of power needed by the engines in order to reach takeoff speed; a number of factors have to be taken into account, including runway length, wind speed, temperature, and most importantly the weight of the aircraft.