TYPE: Business jet.

PROGRAMME: Learjet 31 introduced September 1987 following first flight of aerodynamic prototype (modified Learjet 35A) on 11 May 1987; first production aircraft (N311DF) used as systems testbed; FAA certification 12 August 1988. Learjet 31A and 31A/ER announced October 1990 to replace Learjet 31. Certified in 21 countries, including Argentina, Australia, Bermuda, Brazil, Canada, Czech Republic, Denmark, Germany, Grand Cayman, Guatemala, Indonesia, Italy, Japan, Luxembourg, Mexico, Namibia, Pakistan, Philippines, South Africa, Switzerland and USA. Total fleet time 400,000 hours by 1 October 2000. Will be superseded by Learjet 40 from 2004.

CURRENT VERSIONS: Learjet 31: Original version. No longer produced.
Learjet 31A: Current version.
Description applies to Learjet 31A, except where indicated.
Learjet 31A/ER: Optional extended-range version with 2,627 litres (694 US gallons; 578 Imp gallons) of fuel.

CUSTOMERS: Total of 225 built by September 2003, including 36 of original Learjet 31; 14 Learjet 31As delivered in 1994, 19 in 1995, 13 in 1996, 21 in 1997, 22 in 1998, 24 in 1999, 28 in 2000, 17 in 2001 and nine in 2002. Twenty-one were in the Bombardier FlexJets fleet in early 1999. 200th Learjet 31A delivered 3 October 2000, to Falcon Air Services of Phoenix, Arizona.

COSTS: US$6.419 million, equipped (2000).

DESIGN FEATURES: Small, rear-engined business jet; low wing with leading-edge sweepback; T tail and two large strakes below rear fuselage.
Original Learjet 31 combined fuselage/cabin and power plant of Learjet 35A/36A with wing of Learjet 55; delta fins added to eliminate Dutch roll, stabilise aircraft at high airspeeds, induce docile stall and reduce approach speeds and field lengths; stick pusher/puller and dual yaw dampers no longer required; stick shaker and single yaw damper retained for comfort.
Additional features of Learjet 31A include cruise Mach number up to 13,105 m (43,000 ft) increased 4 per cent to 0.81 and VMO increased from 300 kt (556 km/h; 345 mph) to 325 kt (602 km/h; 374 mph) IAS. Increases mainly benefit descent from high altitudes. Learjet 31A also features integrated digital avionics package.
Improvements announced at the NBAA Convention in Atlanta in October 1999, and incorporated from c/n 31A-194, include: increased maximum T-O weight of 7,711 kg (17,000 lb) and maximum landing weight of 7,257 kg (16,000 lb), latter available for retrofit on earlier aircraft; revised winglet design, based on that of Learjet 60, for enhanced high-speed/high-altitude performance and handling; thrust reversers standard; Universal UNS-1C FMS standard; lighter and more reliable AHRS; dual R134a air conditioning systems to provide increased capacity and redundancy, with one system dedicated to cockpit; and digital engine control for increased reliability and provision of trend monitoring.

FLYING CONTROLS: Conventional and manual. Ailerons have brush seals and geared tabs; electrically actuated trim tab in port aileron. Electrically actuated tailplane incidence control has separate motors for pilot and co-pilot and single-fault survival protection; aircraft can be manually controlled following tailplane runaway and landed with reduced flap. Rudder has electric trim tab; automatic electric rudder assist servo operates automatically if rudder pedal loads exceed 22.6 kg (50 lb). Full-chord fences bracket the ailerons. Single spoiler panel in each wing used as airbrake and lift dumper. Hydraulically actuated flaps extended to 40°. Optional drag parachute mounted on inside of baggage hatch under tail.

STRUCTURE: Semi-monocoque fuselage with eight-spar internal structure; multispar wing with machined skins; winglets have full-depth honeycomb core bonded to skin.

LANDING GEAR: Retractable tricycle gear; main legs retract inward, nose leg forward; twin-wheel main units with anti-skid disc brakes; nosewheel has full-time digital steer-by-wire. Tyres 17.5x5.75-8 (12 ply) main; 18x4.4 (10 ply) nose. Ground turning radius about nosewheel 8.08 m (26 ft 6 in).

POWER PLANT: Two 15.56 kN (3,500 lb st) Honeywell TFE731-2-3B turbofans with N1 digital electronic engine controller giving engine trend monitoring, automatic retention of power settings above 4,575 m (15,000 ft) and special idling control for descent from 15,545 m (51,000 ft). Engine synchroniser fitted. Dee Howard 4000 thrust reverser system standard. One integral fuel tank in each wing standard or ER tank in fuselage; fuselage fuel transferred by gravity or pump; single-point pressure refuelling standard.

ACCOMMODATION: Cabin furnishings include a three-seat divan, four Erda 10-way adjustable individual seats in club seating arrangement, side-facing seat with lavatory, two folding tables, baggage compartment, overhead panels with reading lights, indirect lighting, air vents and oxygen masks. Revised interior offering more headroom and three cabin configurations announced October 1994 and introduced on 100th aircraft May 1995. Aft lavatory option introduced in 1996, providing an additional 0.28 m³ (10.0 cu ft) of baggage space. Optional external baggage locker increases total baggage volume to 1.76 m³ (62.0 cu ft).

SYSTEMS: Hydraulic system operates flaps, landing gear, airbrakes, wheelbrakes and thrust reversers; system pressure 69 to 120.6 bar (1,000 to 1,750 lb/sq in); pneumatic standby for gear extension and wheelbrakes. Normal cabin pressure differential 0.64 bar (9.4 lb/sq in) with automatic flood engine bleed if cabin altitude exceeds 2,820 m (9,250 ft); pop-out emergency oxygen for passengers and masks for crew. Electrical system based on two starter/generators, two lead-acid batteries and two inverters; both busses can run from one engine; electrics operate tailplane incidence, rudder assister and nosewheel steering. Anti-icing by bleed air for wing, engine intakes and windscreen; tailplane electrically heated; fin not protected. Alcohol spray for radome to stop shed ice entering engines; controls prevent internal ice and condensation during long descents.

AVIONICS: Honeywell integrated digital avionics package with five-tube EFIS 50, Universal UNS-1M flight management system (FMS), dual Series III nav/comms, and dual KFC 3100 autopilots/flight directors.

EQUIPMENT: Throttle-mounted landing gear warning mute and go-around switches, nacelle heat annunciator, engine synchroniser and synchroscope, recognition light, wing ice light, emergency press override switches, transponder ident switch in pilot's control wheel, flap preselect, crew lifejackets, cockpit dome lights, cockpit speakers, crew oxygen masks and fire extinguisher are standard.