By 1988, Beechcraft had begun work on the replacement for the 300. The fuselage of the 300 was stretched by nearly three feet with two extra cabin windows on each side and winglets added to the wingtips to create the Model B300, introduced in 1990 and initially marketed as the Super King Air 350. MTOW was increased again to 15, 000 lb (6, 750 kg); as the same regulatory situation that led to the development of the 300LW still existed, that model continued to be produced until 1994. Like the 200 and B200 before it, a version with a large cargo door was developed, the Model B300C marketed as the "Super King Air 350C". The first deliveries of this model also took place in 1990. In 1998, the UltraQuiet active noise canceling system, made by Elliott Aviation, was added as standard equipment on all B300s. In October 2003, Beechcraft announced that it would deliver future B300 and B300C King Airs with the Rockwell Collins Pro Line 21 avionics suite.
