Learjet Corp. created the Model 31 in the mid-1980s by mating the Learjet 35A fuselage to the Learjet 55 “long-horn” wing. The result was a light jet that few competitors could rival for climb performance, high-altitude cruise speed or overall fuel efficiency. Dozens of LR31 pilots proudly wore their “510” lapel pins after cruising at 51,000 ft.
Produced from 1988 to 1991, the aircraft had excellent runway performance and its signature anhedral “delta fins” on the tailcone, plus wing aero mods gave it docile low-speed handling characteristics on a par with the far slower Citation 500/550. The mods eliminated the need for a stall barrier stick pusher and a requirement for an operative yaw damper for dispatch.
The winglet-equipped long horn wing, however, lacked tip tanks, thereby cutting fuel capacity by 2,076 lb. compared to LR35A. NBAA range thus shrank to 1,290 nm from 1,924 nm. Most operators say it’s a comfortable 1,000-nm airplane, leaving them 1,600 lb. of reserves at shutdown. An optional fuselage fuel tank increases capacity by 500 lb., boosting range by 200 nm. The 32-lb. Raisbeck ZR Lite transonic drag-reduction kit can increase range another 100-plus miles. Pilots also say the aircraft will routinely cruise at FL 430-470, letting them soar above most weather and turbulence.
The succeeding Learjet 31A, built from 1991 to 2003, is fitted with Bendix/King avionics, incorporating a rudder boost system that shaves 9 kt. off Vmcg. It is available with an optional weight increase to 17,700 lb. Production of the aircraft ceased when Learjet 45 superseded the last of the small fuselage Learjets.
Grandfathered onto the 1966 Lear 24 type certificate, Model 31A features similar system designs, including a parallel bus, DC electrical system with bus-tie breakers, manually operated bleed-air on/off switches, analog pressurization system, clamshell entry door with motorized closing system, and impressively powerful anti-skid brakes. The optional single-point pressure (SPPR) refueling can be used to fill both wing and fuselage tanks, eliminating the need to use the DC boost pumps to transfer fuel to the fuselage from the wings. Aircraft with SPPR have standard fuel heaters that eliminate the need for a fuel anti-icing additive. The 36-in.-wide entry door is another popular option, as it makes it considerably easier to load and unload bulky items.
Weak points? The aircraft lacks a factory-standard external baggage bay. A Raisbeck aft baggage locker is a popular mod that helps to solve this problem. The forward lavatory is “emergency use only” for modest people as it has forward and aft privacy curtains, rather than a solid door and bulkheads common to aft lavs in other aircraft.
Scheduled maintenance inspections are A/B/C/D checks at 300/600/1,200 and 2,400 hr., respectively, or 12-/24-/48- and 96-month intervals, plus wing and horizontal demate at 12,000 hr. and invasive fuselage x-ray checks at 12 years. Budget $250 per hour for maintenance and $50 per landing for brakes and tires, says Andy Olson, director of maintenance at Trine Aerospace in Colorado Springs. Honeywell MSP Gold runs about $666 per hour for both engines, but some operators with run-out turbofans just buy used TFE731-2 engines that run about $120 per hour for time remaining to 1,400-hr. MPI or 4,200-hr. CZI (overhaul).
What breaks? Starter-generators usually need overhauling at 1,000 hr., or well before the 1,400-hr. scheduled maintenance intervals. Hydraulic flap, spoiler and landing gear actuators are prone to leak, the vapor cycle air-conditioner compressor and lines deteriorate, causing leaks and the electric de-ice boots on the horizontal stab may fail as they age. Plan to locate a large stash of spare parts long before anything goes awry, savvy operators say.
Competition in this class is tough, in spite of Model 31A’s clear performance advantages. It vies with the Citation II and S/II which have considerably larger cabins and factory-standard external baggage compartments, but cruise at much slower speeds. The S/II also has more range. Beechjet 400/400A have much roomier cabins, almost as much speed and about the same range. Learjet 35A has 450 mi. more range than the extended range version, but it cannot climb as high because of extra weight and poorer wing performance. Citation V is the toughest competitor in class, having great TOFL performance, a much longer cabin, good cruise speed and more range. But it is also considerably more expensive.
Learjet 31A commands about $650,000-800,000 in the resale market, depending upon condition, maintenance status and remaining engine life. The 12-year fuselage and 12,000-hr. wing demate procedures each cost between $150,000 and $200,000, depending upon squawks, so be mindful when reviewing the maintenance log books. Aircraft enrolled in Honeywell MSP are worth considerably more than those not covered by engine programs.
Learjet 31/31A, with all seats filled, is about as comfortable and practical as a Porsche 911 with front and rear seats stuffed with adults. With few people aboard, though, it’s also about as much fun to fly as the Zuffenhausen blitz-wagen is to drive on the autobahn. So, if you’re a need-for-speed pilot, this is your kind of light jet. But if you’re searching for an aircraft with a comfy cabin and one-stop transcon U.S. range, this vintage hot rod might come up short.
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