The Model 90 King Air was conceived as the Model 120 in 1961. In May 1963, Beechcraft began test flights of the proof-of-concept Model 87, a modified Queen Air with Pratt & Whitney Canada PT6A-6 engines. On July 14, Beech announced a new type, and a month later began accepting orders for the "King Air", with deliveries to commence in Autumn 1964. On January 24, 1964, the first definitive prototype, by now designated Model 65-90 and also fitted with PT6A-6 engines, flew for the first time. After 10 months of test flying, in 1964 the Model 87 was delivered to the United States Army as the NU-8F. The first production aircraft was delivered on October 8, and by the end of the month, 152 aircraft had been ordered; by year's end, seven had been built.

In 1966, after 112 65-90s were completed, production switched to the Model 65-A90 with PT6A-20 engines. As a measure of the type's popularity, 206 65-A90s were built in less than two years when production switched to the Model B90, the first of these rolling off the production line in 1968. Military versions built during these years included the 65-A90-1, 65-A90-2, 65-A90-3, and 65-A90-4, all being unpressurised models based on the Model 87. These were produced for the US Army which designated them U-21s of various sub-models; many were fitted out for electronic battlefield surveillance. A total of 162 of these were built between 1967 and 1971.

A total of 184 B90 models were produced before the Model C90 was introduced in 1971, with wingspan increased over earlier models by 4 ft 11 in (1.50 m) to 50 ft 3 in (15.32 m), Maximum Take-Off Weight (MTOW) increased by 350 lb (160 kg) to 9,650 lb (4,378 kg), and PT6A-20A engines. The broadly similar Model E90 was introduced the following year, with PT6A-28 engines; the two were produced in parallel. Further refinement of the 90 series resulted in the Model F90 and follow-on Model F90-1. The F-models featured the T-tail of the Model 200 King Air mated to the fuselage and wings of the E90, with PT6A-135 engines of 750 shp (560 kW) driving four-bladed propellers. The F90 prototype flew on January 16, 1978 and 203 production versions followed between 1979 and 1983, when the F90 was superseded by the F90-1. The F90 prototype was re-engined with Garrett AiResearch TPE-331 engines to test the feasibility of a Model G90, but this model was not put into production.

The Model C90-1 entered production in 1982 after 507 C90s and 347 E90s had been built, and featured PT6A-21 engines and improvements to the pressurization system. 54 were built. The following year the F90-1 was put into production with redesigned engine cowlings, upgraded PT6A-135A engines, hydraulic landing gear, and triple-fed electrical bus; only 33 were built by the time production terminated in 1985. The C90-1 was soon followed by the Model C90A, which featured the redesigned engine cowlings of the F90-1. The C90A received an increase in MTOW in 1987, being certified to 10,100 lb (4,580 kg). The C90A model was in production until 1992, by which time 235 had been built, all but 74 with the increased MTOW.

Only two C90As were built in 1992, the Model C90B followed that year with airframe improvements, four-bladed propellers, and propeller synchrophasing, all in an effort to reduce cabin noise. This model also had PT6A-21s; the first production C90B was fitted with the 10,000th PT6 engine delivered to Beechcraft. In 1994 a cheaper version was introduced as the C90SE (Special Edition), with three-bladed propellers, standardised interior and mechanical instruments instead of the Electronic Flight Instrument System (EFIS) fitted to the C90B. A total of 456 C90Bs and C90SEs were delivered by the time production of these models ended in late 2005.

In July 2005, during the Oshkosh Airshow, Beechcraft introduced the C90GT. The C90GT was fitted with 750 shp (560 kW) PT6A-135As, flat rated to the same 550 shp (410 kW) as the earlier King Airs. This engine change increased performance due to lower operating temperatures, improving both cruise speed and climb rate. With a 275 kt (509 km/h, 316 mph) cruise speed, the C90GT was highly competitive with the new generation of Very Light Jets over short to medium distances, while providing a larger and more luxurious cabin. C90GT deliveries commenced at the beginning of 2006. On May 21, 2007, during the 7th Annual European Business Aviation Convention & Exhibition in Geneva, Beechcraft announced the Model C90GTi updated version of the C90GT, featuring the Rockwell Collins Proline 21 avionics package previously only offered for the B200 and B300 King Airs. Deliveries commenced in 2008 after 97 C90GTs were delivered to customers over the previous two years.

SOURCE: Wikipedia