Evergreen Air Center is the world's largest parking lot for unwanted commercial aircraft. Airlines pay from $750 to $5,000 monthly for the storage services provided by Evergreen. Prior to September 2001, the company had 140 discarded airplanes at its Arizona facilities and was growing at a rate of about six planes monthly with about two a month sold for parts and/or scrap metal. After calamity struck the airline industry in September 2001, the airlines have retired over a thousand planes-many of which found their way to Evergreen. Now the actual number of planes stored at Evergreen differs significantly from the prediction based on previous behavior. This difference is referred to as ??