The Learjet family began with the original six to eight seat Lear Jet 23 which first flew on October 7 1963. The diminutive Model 23 pioneered an entirely new market segment for the light business jets, and proved very successful. The first production 23 was delivered in October 1964, but was replaced by the improved Lear Jet 24 for private jet charter in 1966 after 105 had been built. The LearJet 24, which introduced uprated engines and a number of detail changes, first flew in February 1966 and was delivered from the middle of that year. Developments of the LearJet 24 included the Lear Jet 24D, Lear Jet 24E and Lear Jet 24F, introducing improvements such as increased weights, thrusts, and range.
The Learjet 25 introduced a 1.27m (4ft 2in) fuselage stretch allowing seating for up to eight passengers and was first flown on August 12 1966, and, like the 24, a number of subsequent developments were built, including the B, C, and D. In 1966 the name of the manufacturer changed to Lear Jet Industries, and in January 1970 Gates Rubber Company, who had bought a controlling interest, changed the name again, to Gates Learjet Corporation.
The unsuccessful Gates Learjet 28 and 29 Longhorns are based on the 25 but introduced a new increased span wing fitted with winglets, which improved fuel efficiency and overall performance, particularly payload range and fuel economy. The Longhorn 28 seats up to eight passengers, the similar dimensions Longhorn 29 sacrifices two seats for extra range. Production of the family ceased in 1982. Learjets are known for their tight accomodation. Max internal cabin width is just 1.50m (4ft 11in), max height 1.32m (4ft 4in).