 In the 1990s, eight 727 freighters were converted (at a cost of $2.5 million each) into 727-100QC (QC=Quick Change) freighters with the ability to be re-converted into passenger aircraft for the purpose of chartered flights.After disappointing results, in 2001, UPS ended charter service with quick-change freighters, with the aircraft returned to cargo service.Following the addition of primary and secondary hubs to the airline network during the 1990s, for much of the next decade, additional demand led to massive expansion of its central Louisville air hub.