The number of passengers transported by air has increased tremendously during the last decades. In the mid-seventies there were only slightly more than 200 million passengers transported by air in the EU-15. An estimation for 2000 gives a number of about 600 million. The effects of the tragic events of the 11 September 2001 are negative, estimates give that between 2000 and 2001, the total number of passengers carried decreased by 2 %.