The French Air Force (Armée de l'Air) frequently train to fly at low level. Across France there are a network of connected 10km wide military training areas where military aircraft are cleared down to as low as zero feet, for front line fast jets however there is normally a 250 feet (76m) Above Ground Level (AGL) or Above Surface (ASFC) limit. While instructors training on the Alpha Jet are cleared down to 250 feet student pilots have a minimum height of 500 feet ASFC. Military aircraft can fly at very high speed (très grande vitesse) and at very low altitude (très basse altitude) consequently the principle 'of seeing and of avoiding' (principe "voir et éviter") is not applicable in these areas. The numbered training corridors or zones are not continually in operation but individually activated at different times on a day by day basis.