tunnel testing were performed upon the supercritical wing alone. Launch Backed by the federal government, the programme was launched on 29 October 1976 with firm orders and deposits for 53 aircraft. Within the next two years, roughly 2,500 employees would be involved in designing the aircraft. Various changes to the original Learstar configuration had been made on the run up to launch, such as the conventional tailplane being substituted for a T-tail counterpart after the former was found to be in the path of the engine's exhaust flow, the relocation of fuel storage to the wings, and multiple increases of the aircraft's gross weight. Following disagreements over the direction of the programme, Bill Lear was phased out of involvement; accordingly, in March 1977, the aircraft was renamed the Challenger 600. Reportedly, following his disassociation with the venture, Lear referred to Canadair's revised design as Fat Albert. Following Lear's death in May 1978, Canadair paid an estimated $25 million to his estate for his contribution to the programme. Due to the expansion of the design, the original powerplant configuration became untenable; thus, engine manufacturer Lycoming proposed developing a new model, the Lycoming ALF 502L, which Canadair's design team accepted for the enlarged Challenger, and around which drew up its general arrangement. The type's wide cargo door had been designed in response to the needs of FedEx, the type's original launch customer, having placed an order for 25 aircraft. Additionally, FedEx had experienced problems with the General Electric CF34 engines, and favoured the Lycoming ALF 502D, instead; those later had delivery troubles and lacked performance. Reportedly, FedEx converted most of its orders into the Challenger's stretched version, intending to carry up to 12,500 lb of freight at a time using them. However, FedEx ultimately opted to cancel its orders due to the US Airline Deregulation Act, and the specific aircraft that were already in production were sold to other customers, instead. By the spring of 1977, Canadair had received over 70 firm orders and had begun constructing three prototypes. Furthermore, a $70 million loan was borrowed from European sources to help finance the programme, which lessened the financial burden on the Canadian government. A full-scale fuselage mockup was displayed at the 1977 Paris Air Show before a European and North American tour, and 106 had been sold by 1977 end. During late 1977, in the face of criticism that the project would