Airports: Austrian civil airports are located in Vienna-Schwechat, Graz-Thalerhof, Innsbruck-Kranebitten, Klagenfurt-Annabichl, Linz-Hoersching and Salzburg-Maxglan. In the vicinity of Bregenz, just across the Swiss border is the airport of Altenrhein; the airports of Graz and Linz are also used for military purposes, military airfields are located in Langenlebarn, Wiener Neustadt, Aigen and Zeltweg. In addition Austria boasts several helicopter airbases as well as club aerodromes. Austria's largest airport, Vienna-Schwechat, handled approximately 9.7 million passengers in 1997 ( Flughafen Wien AG). All of Austria's airports have imposed take-off restrictions for noisy airplanes between 6.00-23.30.