[6] The 350ER (B300CER[5]) is available to government, military and commercial customers for special mission operations[7] such as aerial survey, air ambulance, flight inspection and surveillance.

BB-186;[16] the modifications included changes to the belly aft of the wing to allow photography with a vertical camera, provision for a surveillance radar in a pod under the fuselage, dome-shaped windows on the sides of the rear fuselage to allow observation directly below the aircraft by occupants, and a 50-US-gallon (190 L) usable capacity fuel tank on each wingtip to increase the aircraft's range.

[20] Commencing in 1984 the B200, B200C and their derivatives were fitted with a revised landing gear retraction mechanism, actuated by hydraulic rams powered by an electric pump installed in the LH wing.

[11] This replaced the earlier electro-mechanical retraction system of gearboxes, driveshafts and chains and sprockets that was a throwback to the Twin Bonanza.

[20] A total of 14 B200s were produced in 1989 and 1990 in a 13-seat high density configuration with a belly cargo pod; these were marketed by Beechcraft as a commuter airliner under the designation Model 1300.

[21] From October 1995 Beechcraft offered an updated B200 with Electronic Flight Instrument System (EFIS) avionics, this was marketed as the "B200SE Super King Air" (for Special Edition).

[25][26] On May 21, 2007, during the 7th Annual European Business Aviation Convention & Exhibition in Geneva, Hawker Beechcraft (as the company was now known) introduced the Model B200GT updated version of the B200.

The B200GT and B200CGT with large cargo door were certified by the Federal Aviation Administration (FAA) on November 16, 2007[21] and by the end of 2009, 97 B200GTs had been delivered.

The upgrade puts the 250EP into the same weight class as the King Air 350, necessitating various system changes to meet certification requirements and a special rating for pilots.

The model has an improved autothrottle, a Multi-Scan weather radar, a range of 1,720 nmi (3,190 km) and a top cruise speed of 310 kn (570 km/h) with up to nine passengers.

The first two were conversions of standard Model 300s, while the remaining 17 were purpose-built; since they were delivered the FAA has used the fleet to check the extensive network of navaids in the United States.

200 and 300 Series King Airs have been used for similar duties in several other countries or regions, including Australia, Germany, Hong Kong (a B200C used for navaid calibration was the first aircraft to land at the then-new Chek Lap Kok Airport in 1996[22]), Norway, Sweden and Taiwan.

It has two extra cabin windows on each side and MTOW was increased again to 15,000 lb (6,800 kg); as the same regulatory situation that led to the development of the 300LW still existed, that model continued to be produced until 1994.

In 1998, the UltraQuiet active noise canceling system,[41] made by Elliott Aviation, was added as standard equipment on all B300s.

[42] In October 2003, Beechcraft announced that it would deliver future B300 and B300C King Airs with the Rockwell Collins Pro Line 21 avionics suite.

[48] In October 2008, Beechcraft announced updated versions of the B300 series, the King Air 350i, with improvements to the passenger cabin.

The cabin also includes Universal Serial Bus (USB) ports, AC electrical receptacles and fold-out tables for each passenger in the eight seats fitted.

The $1.8 million Blackhawk PT6A-67A upgrade offers a 68 kn (126 km/h) TAS faster cruise and up to 60% shorter time to climb.

The Hawker Pacific aviation company of Australia purchased eight B300s between 2003 and 2005 for lease to the Royal Australian Air Force (RAAF), which were subsequently modified as navigator trainers.

The United States Army has contracted for a number of King Air 300s to be acquired on the second-hand market and modified as ISTAR aircraft for use by Task Force ODIN in operational theaters.

[65][66] Extended range special mission version for surveillance and reconnaissance operations, introduced at the Paris Air Show in June 2005.

Features engine nacelle fuel tanks, heavy duty landing gear and increased maximum take-off weight of 7,484 kg (16,500 lb).

Accommodation includes two pilots above an armoured floor; sensor operator at console (port, forward facing) providing on-board analysis; club-four seating in centre section with port side table, satellite telephone and refreshment centre; and lavatory at rear.

[72] Canada intends to use the aircraft to improve the ability of its Special Operations Forces Command (CANSOFCOM) to meet current and future threats, strengthen its homeland defense and the combined defense of North America and support coalition partners overseas.

[73] The King Air 360 and 360ER have a cockpit including an avionics upgrade, digital pressurisation and an autothrottle; and a modernised cabin featuring a 10% lower altitude pressure.

Raisbeck Engineering out of Seattle, WA offers Enhanced Performance Leading Edges, Nacelle Wing Lockers, Ram Air Recovery System, Quiet Turbofan Propellers, High Flotation Gear Doors and Dual Aft Body Strakes.

[81] In November 2019, Textron Aviation introduced a modified nose holding 12 cu.ft (0.34 m3) or 250 lb (113 kg) of cargo or aircraft equipment.

It was intended to be replaced by the unusually designed Beechcraft Starship but only 53 were produced, ending in 1995, while the King Air continues to sell.

[85] By April 2017 sales of the King Air series were in decline with just 12 examples delivered in the first quarter of the year, compared to 26 in the same period of 2016, due to a weak international market for the design.

The King Air is used by many corporate and private users, it is also popular as a light transport liaison aircraft with both government and non-government organizations.