X-Plane 9 – Learjet 23 v2.0. The Lear 23 is an American six-to-eight-seat (two crew and four to six passengers) twin-engine, high-speed business jet manufactured by Learjet. The first flight of the Learjet 23 took place on 7 October 1963 with test pilots Hank Beaird and Bob Hagen. Production of the Learjet 23 stopped in 1966 after a total of 104 had been built. In 1998 there were still 39 Model 23s in use. By Larry Cole.