Originally Posted by coast in

Airlines have historically retired airframes right around the 30 year mark. Lots of factors go into this. 3rd heavy check happens right around 30 years and they usually find 30 years of acummulated problems when they open them up. Northwests DC9's, FedEx's 757's and, yes, United's 767-300's are the exceptions. The mid 1990's UAL A320's are probably the second least reliable fleet in the airline, after the early 1990's 767-300's. These aircraft aren't being 'parked', they are being retired. This nothing new in the Airline world.