At the end of 1975, Canadair began funding the development of LearStar 600, and then bought the design for a wide-cabin business jet in April 1976.In March 1977, it was renamed the Challenger 600 after Bill Lear was phased out, and the original conventional tail was changed for a T-tail among other developments.The flight test program saw a deadly crash on 3 April 1980, but Transport Canada approved the CL-600 type certification on 10 August 1980.The Challenger is a low-wing jet powered by two turbofans mounted in aft fuselage pods, with a supercritical wing and a stand-up cabin with two seating sections.The original Lycoming ALF 502 turbofans were replaced by a pair of General Electric CF34s on the CL-601, which also gained winglets, and first flew on 10 April 1982.Around 1974, American aviation inventor Bill Lear conceptualised the LearStar 600, a low-wing, long-distance business jet, which was powered by a pair of Garrett TFE731-1 geared turbofan engines and equipped with a supercritical wing.[2][3] Lear lacked the capabilities to launch such an aircraft, thus sought out other agencies to collaborate with to both produce and sell it, including the Canadian aerospace manufacturer Canadair.According to authors Ron Picklet and Larry Milberry, Canadair's top management were of the opinion that Lear's concept was sketchy at best.[5] Following a study, contrasting the proposed Learstar against rivals such as the Lockheed Jetstar, Dassault Falcon 50, and Grumman Gulfstream II, Canadair decided to give its backing to the idea near the end of 1975.[3] Perhaps more importantly, the Canadian government had issued a demand that Canadair become self-sufficient, thus the company wanted to depend less upon subcontracting arrangements with other firms, such as France's Dassault Aviation and America's Boeing, or providing support packages for existing aircraft for which they had already ended production, such as the CF-5 fighter.[3] Canadair planned to use Lear's name and skills at self-promotion to secure extensive financial guarantees for a business-jet project from the Canadian federal government.[3] Changes to the original Learstar configuration had been made on the run up to the 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.[3] 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.[2] In late 1977, in the face of criticism that the project would not be capable of producing an aircraft fulfilling the performance guarantees made, Canadair officials had commented that they expected the first flight to occur in 1978, and that initial deliveries had been scheduled to begin during September 1979.The aircraft crashed due to the failure of the release mechanism to detach the recovery chute after a deep stall, killing one of the test pilots.[15] According to Flight International, the slow initial sales of the Challenger heavily contributed to the near-bankruptcy of Canadair, which was only avoided by the purchase of the company by Bombardier in 1986.[3] While the Challenger is generally similar in configuration to previous aircraft of its type, some of its features stand out; for example, a widened fuselage allows a "walk-about cabin".It was also designed to easily accommodate Canadair's early plans to stretch the fuselage, for which equal-length plugs are installed fore and aft of the centre section to greatly increase the Challenger's capacity.Early examples feature luxuries such as telephones, lighting controls, and stereo systems; foldaway tables attached to the cabin walls were also installed, along with a pair of wardrobes, one fore and one aft, for storing hand luggage and other small items.