TYPE: Medium-range business jet.

PROGRAMME: First flight of first prototype Learjet 55 (N551GL) 19 April 1979; first flight of second prototype (N552GL) 15 November 1979; first flight of production aircraft 11 August 1980; FAR Pt 25 certification 18 March 1981; first delivery 30 April 1981. Phase 1 performance improvement package, certificated July 1983, included new triangular-wedge stall strips, automatic ground spoilers and automatic power reserve; Phase 1A performance improvement package, introduced Spring 1984, includes high-energy, long-life brakes and modified landing gear; optional max T-O weight of 9,752 kg (21,500 lb) and max landing weight of 8,165 kg (18,000 lb) introduced from aircraft c/n 55-107; final Learjet 55C, No. 147, delivered December 1990 to UK; Learjet 55C being superseded by Learjet 60 in 1992.

VARIANTS: Learjet 55B: Announced September 1986; optional max T-O weight became standard, wing improved, new interior, all-digital (light deck, better take-off performance, increased range and better mission flexibility. Details in 1987-88 Jane's.
Learjet 55C: Announced September 1987; incorporated Delta Fins which improved stability at all speeds, eliminated Dutch roll, softened stall, reduced approach speeds and ended need for stick puller/pusher and dual yaw dampers at departure.
Learjet 55C/ER: Extended range version with additional 163 kg (359 lb) fuel tank in tailcone baggage compartment; can be retrofitted.
Learjet 55C/LR: As 55C/ER, but with additional 386 litre (102 US gallon; 85 Imp gallon) tank between standard fuselage tank and ER optional tank; can he retrofitted; typical seating for seven and two crew.

DESIGN FEATURES: Sweepback 13° at quarter-chord, advanced cambered leading-edge; Delta Fins, Softflite package and supercritical winglets; Anti-icing of wing leading-edge by engine bleed air and of tailplane leading-edge by electric heating.

FLYING CONTROLS: Manual flying controls with electric trim tabs on port aileron and rudder, electrically actuated variable incidence tailplane; hydraulically actuated slotted trailing-edge flaps; spoilers ahead of flaps.

STRUCTURE: Multi-spar wing with cavity-milled skins; upper skin tapers in thickness towards tip; semi-monocoque rail-safe fuselage.

LANDING GEAR: Hydraulically retractable tricycle type, with twin wheels on each main unit and single steerable nosewheel (±55°). Mainwheel tyres size 17.5 x 5.75-8, 12 ply, pressure 12.4 bars (180 lb/sq in); nosewheel tyre size 18.0 x 4.4, 10 ply, pressure 7.24 bars (105 lb/sq in). High pressure pneumatic system for emergency extension. Oleo-pneumatic shock absorbers. Chined nosewheel tyre. Mainwheel doors are of composites construction. High energy hydraulic braking system, with pneumatic backup. Fully modulated anti-skid units.

POWER PLANT: Two Garrett TFE731-3A-2B turbofans, each rated at 16.46 kN (3700 lb st), plus 0.80 kN (180 lb st) automatic power reserve, pod-mounted on sides of fuselage aft of wing. Thrust reversers standard. Fuel in integral wing tanks and a fuselage bladder tank, with a combined usable capacity of 3,782 litres (999 US gallons; 832 Imp gallons) in standard Model 55C; 3,982 litres (1,052 US gallons; 876 Imp gallons) in Model 55C/ER. 4,353 litres (1,150 US gallons; 957 Imp gallons) in Model 55C/LR. Single-point refuelling. Engine nacelle leading-edges and fan hubs anti-iced by engine bleed air.

ACCOMMODATION: Crew of two on flight deck, with dual controls. IPECO fully adjustable crew seats. Seating for four to eight passengers in a choice of six interior layouts. Two folding tables. Carpeted floor. Galley refreshment cabinet. Toilet. Baggage space at rear of cabin, and in fuselage nose and tailcone of basic Model 55C. Tailcone baggage space reduced on long-range versions, but 55C/LR has baggage area at front of cabin. Two-piece clamshell door at forward end of cabin on port side, with integral steps built into the lower section. Emergency exit/baggage door on starboard side of cabin.

SYSTEMS: Environmental control system comprises cabin pressurisation, ventilation, heating and cooling. Heating and pressurisation are provided by engine bleed air, with a maximum pressure differential of 0.65 bar (9.4 lb/sq in), maintaining a cabin altitude of 2,440 m (8,000 ft) to 15,545 m (51,000 ft). Freon vapour-cycle cooling system, supplemented by a ram air system. Anti-icing system includes distribution of engine bleed air to wing leading-edges, engine nacelle leading-edges and fan hubs, and pilot and co-pilot windscreens; electric anti-icing of tailplane leading-edge, pitot heads, stall warning vanes and static ports; and alcohol anti-icing of windscreens. Hydraulic system supplied by two engine driven variable-volume constant-pressure pumps, one on each engine, each 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 28V 400A engine driven brushless generators, either of which is capable of maintaining adequate DC power to operate all electrical services; two 1kVA solid state inverters to provide AC power; and two 24V 37Ah lead-acid batteries. Oxygen system of 1.08 m³ (38 cu ft) capacity, with crew demand masks, dropout mask for each passenger, which is presented automatically if cabin altitude exceeds 4,265 m (14,000 ft). Sundstrand Turbomach APU optional (not on 55C/ER or 55C/LR).

AVIONICS: From aircraft c/n 134 onwards standard avionics include a Collins five-tube EFIS-85L-12 electronic flight instrumentation system with dual AHS-85 AHRS; Collins APS-85 digital autopilot with glareshield controller and dual flight data computers; dual ADC-82 air data systems; dual VHF-22A nav/coms with CTL-22 controls; dual VIR-32 nav receivers with CTL-32 controls; dual DME-42 with IND-42C indicators; ADF-60 with CTL-62 control; dual RMI-30; dual TDR-90 transponders with CTL-92 controls; ALT-55B radio altimeter. Collins WXR-350 Sensor weather radar. Universal UNS-1A long-range nav system; Bendix/King KHF 950 HF; Frederickson Jetcal-5 secal; Collins flight profile advisory system; and Wulfsberg Flitefone VI. Other standard flight deck equipment includes dual Collins encoding altimeters; MSI-80 Mach/airspeed indicators; VSI-80 instantaneous vertical speed indicators; Collins altitude pre-selector/alerter; TAS/SAT/TAT temperature indicator; IDC two-inch standby Mach/IAS indicator and altimeter; J.E.T. PS-835D and AI-804 emergency battery and attitude gyro; dual marker beacon systems; dual Avtech audio systems; dual Davtron 877 clocks; yaw damper; dual stall warning indicators; engine synchroniser and synchroscope; annunciator panels; avionics master switch; Nt reminder, chip detector and flap preselect.

EQUIPMENT: Standard equipment includes sun visors; map lights; life jackets; fire extinguisher; writing tables; dome lights; oxygen masks; manual storage compartments, and dividing panel between flight deck and cabin. Cabin equipment includes two folding tables; four individual seats with tracking, swivel, recline and sideways motions; three-seat forward facing divan with storage and tracking and recline motions, single side-facing seat, galley refreshment cabinet with decanters, bottle cooler, ice chest, oven, tray carrier, hot and cold liquid containers and storage area; forward coat closet; stereo and tape storage; magazine rack; convenience panel with reading lights, air vents, cabin speakers and oxygen masks; lighting control panel; opaque and tinted window shades; indirect lighting; aisle lighting; entrance step light; flushing toilet with vanity mirror and light; baggage compartment light; passenger life jackets; auxiliary cabin heater; fire extinguisher and axe; nose and tail baggage compartment lights; wing ice light and maintenance interphone jack plug sockets.