 The Model 45 was developed to make Learjets fundamentally more competitive against newer designs from competing manufacturers.But, as a clean-sheet design (starting from scratch), being built to more rigorous (FAR Part 25) rules, than previous Learjets, the aircraft's development took substantially greater time than the development of previous Learjet models.The development of the LJ45 began in 1989, but was not announced by Bombardier until September, 1992.