)Previous Learjet designs had used rigorous, extensive "fail-safe" structures in the wing and tail assemblies, with numerous wing spars providing a highly reinforced structure (derived from the Swiss-designed P-16 prototype fighter that was the original basis for the first Learjet) – but the Model 45, instead, used a lighter, less-robust structure, affording less cost in manufacture and lower aircraft empty weights, resulting in improved capacity, efficiency and some performance enhancement (for a given amount of engine power), at a competitive price.Outwardly, however, the Model 45 retained the traditional Learjet appearance, with its semi-swept wing, T-tail, sharp nose, and wrap-around windshield – while using engines and avionics similar to those in the Model 60.