US Air Force designation: C-21A

TYPE: Light twin-turbofan business jet.

PROGRAMME: First flight of first turbofan Learjet (known as Model 26 and using Garrett TFE731-2s), 4 January 1973; production 35 and 36, differing in fuel capacity and accommodation, announced May 1973; FAA certification July 1974; French and UK certification 1979.

VARIANTS: Learjet 35A and 36A: Current production models of 35 and 36, with higher standard max T-O weight.
C-21A: USAF received 80 Model 35As on lease in 1984-85 and purchased them for $180 million in September 1986; used as Operational Support Aircraft for priority cargo, medevac and personnel transport, replacing T-39 Sabreliners; four more C-21As bought 1987 to replace T-39s at Andrews AFB, Maryland.

CUSTOMERS: Eight 35A/36A delivered 1990, bringing total to 720.

DESIGN FEATURES: Softflite package includes full-chord shallow fences bracketing ailerons, with arrowhead energisers on leading-edges and two rows of boundary layer energiser strips between fences. Wing section NACA 64A109 with modified leading-edge; dihedral 2° 30'; incidence 1°; sweepback at quarter-chord 13°. Wings de-iced by engine bleed air; tailplane electrically anti-iced.
Century III improvements, Softflite low-speed handling package and engine synchronisers now standard for both models; higher max T-O weight of 8,300 kg (18,300 lb), originally optional, now standard; improvements introduced in 1983 include T/R-4000 thrust reversers with standby hydraulic power reservoir, single-engined reverse capability, quick removal hot section, prevention of reversal at high thrust, reverse available within two seconds of touchdown, throttle retard system and reverse thrust at reduced gas generator rpm Special interior introduced 1985 offers better leg and headroom. Erda 10-way adjustable seats, stereo and in-flight telephone, lavatory enclosed by doors and electronically controlled washbasin cabinet.

FLYING CONTROLS: Manually actuated flying controls, balance tabs in both ailerons and electrically operated trim tab in port aileron; electrically actuated variable incidence tailplane; electric trim tab in rudder, small ventral fin; hydraulically actuated single-slotted flaps, hydraulically actuated spoilers ahead of flaps.

STRUCTURE: All-metal; eight spar wing with milled skins; fail-safe fuselage.

LANDING GEAR: Retractable tricycle type, with twin wheels on each main unit and single steerable nosewheel, maximum steering angle 45° either side of centreline. Hydraulic actuation, with backup pneumatic extension. Oleo-pneumatic shock absorbers. Goodyear multiple-disc hydraulic brakes. Pneumatic emergency braking system. Parking brakes. Fully modulated anti-skid system.

POWER PLANT: Two Garrett TFE731-2-2B turbofans, each rated at 15.6 kN (3,500 lb st), pod-mounted on sides of rear fuselage. Fuel in integral wing and wingtip tanks and a fuselage tank, with a combined usable capacity (Learjet 35A) of 3,500 litres (925 US gallons; 770 Imp gallons). Learjet 36A has a larger fuselage tank, giving a combined usable total of 4,179 litres (1,104 US gallons; 919 Imp gallons). Refuelling point on upper surface of each wingtip tank. Fuel jettison system. Engine nacelle leading-edges anti-iced by engine bleed air.

ACCOMMODATION: Crew of two on flight deck, with dual controls. Up to eight passengers in Learjet 35A; one on inward facing seat with toilet on starboard side at front, then two pairs of swivel seats which face fore and aft for take-off and landing, with centre aisle, and three on forward-facing couch at rear of cabin. Two forward storage cabinets, one on each side; refreshment cabinet with hot and cold cup storage, coffee warmer, water dispenser, ice chest and serving surfaces; and two folding tables, standard. Alternative arrangement, available optionally, places a refreshment area in the middle of the cabin, accessible from fore and aft club seating areas, each for four passengers. Learjet 36A can accommodate up to six passengers, one pair of swivel seats being removed. Toilet and stowage space under front inward facing seat which can be screened from remainder of cabin. Refreshment cabinet opposite this seat, aft of passenger door. Baggage compartment with capacity of 226 kg (500 lb) aft of cabin. Two-piece clamshell door at forward end of cabin on port side, with integral steps built into lower half. Emergency exit on starboard side of cabin. Birdproof windscreens.

SYSTEMS: Environmental control system comprises cabin pressurisation, ventilation, heating and cooling. Heating and pressurisation by engine bleed air, with a max pressure differential of 0.65 bar (9.4 lb/sq in), maintaining a cabin altitude of 1,980 m (6,500 ft) to an actual altitude of 13,715 m (45,000 ft). Freon R12 vapour cycle cooling system supplemented by a ram-air heat exchanger. Flight control system includes dual yaw dampers, dual stick pushers, dual stick shakers and Mach trim. Anti-icing system includes distribution of engine bleed air for wing, tailplane and engine nacelle leading-edges and windscreen; electrical heating of pitot heads, stall warning vanes and static ports; and alcohol spray on windscreen and nose radome. Hydraulic system supplied by two engine driven pumps, each pump capable of maintaining alone the full system pressure of 103.5 bars (1,500 lb/sq in), for operation of landing gear, brakes, flaps and spoilers. Hydraulic system maximum flow rate 15 litres (4 US gallons; 3.33 Imp gallons) per min. Cylindrical reservoir pressurised to 1.38 bars (20 lb/sq in). Electrically driven hydraulic pump for emergency operation of all hydraulic services. Pneumatic system of 124 to 207 bars (1,800 to 3,000 lb/sq in) pressure for emergency extension of landing gear and operation of brakes. Electrical system powered by two 30V 400A brushless generators, two 1kVA solid state inverters to provide AC power, and two 24V 37Ah lead-acid batteries. Oxygen system for emergency use, with crew demand masks and dropout masks for each passenger.

AVIONICS: Standard Collins avionics include dual FIS-84/EHSI-74 flight directors, integrated with J.E.T. FC-530 FCS and dual yaw dampers; dual VHF-22A com transceivers with CTL-22 controls; dual VIR-32 nav receivers with CTL-32 controls; ADF-60 with CTL-62 control; dual DME-42 with IND-42C indicators; dual TDR-90 transponders with CTL-92 controls; ALT-55B radio altimeter with DRI-55 indicator; dual Allen 3137 RMIs; UNS-1 long-range nav system; Honeywell Primus 450 colour weather radar; dual J.E.T. VG-206D vertical gyros; dual J.E.T DN-104B directional gyros; pilot's IDC electric encoding altimeter with altitude preselect and IDC air data unit, co-pilot's IDC barometric altimeter; dual Teledyne SL2-9157-3 IVSIs; dual marker beacon lamps; dual D/B audio systems; J.E.T. PS-835D emergency battery and Al-804 attitude gyro; dual Davtron 877 clocks; annunciator package; N₁ reminder; avionics master switch; chip detector; flap preselect; Wulfsberg Flitefone VI; Bendix/King KHF 950 HF; Frederickson Jetcal 5 Selcal; Rosemount air data system and SAS/TAT/TAS indicator.

EQUIPMENT: Standard equipment includes thrust reversers, dual angle of attack indicators, engine synchronisation meter, cabin differential pressure gauge, cabin rate of climb indicator, interstage and turbine temperature gauges, turbine and fan speed gauges, wing temperature indicator, alternate static source, depressurisation warning, engine fire warning lights. Mach warning system, dual stall warning system, fire axe, cabin fire extinguisher, cabin stereo cassette player, EEGO audio distribution system, flotation jackets for crew and passengers, sound-proofing; baggage compartment, courtesy, instrument panel, flood, map, cockpit dome, and reading lights; dual anti-collision, landing, navigation, recognition, strobe, taxi and maintenance lights, wing ice detection light; dual engine fire extinguishing systems with 'systems armed' and fire warning lights, maintenance interphone jack plugs, engine synchronisation system, control lock, external power socket, and lightning protection system.