The Learjet 24 earned a reputation for being a flying limousine. This business jet is the first mature version of the early Learjet generation, building upon the revolutionary features of the 1964 Learjet 23. Between 1966 and 1977, Learjet delivered 259 units of Model 24. According to the Federal Aviation Agency, over 100 were still airworthy in 2022.
Bottom Line Up Front
The Learjet 24 was the first mature Learjet design. The aircraft quickly became the most popular light business jet in the world after its introduction in 1966 and held this position for many years until the Learjet 35 unseated it.
This fast and sleek private jet is one of the most influential aircraft in history, with “Learjet” becoming synonymous with luxury and performance.
The Learjet 24 is fast for executive standards, but this comes as no surprise when considering the history of the aircraft. Bill Lear adapted work from a little-known Swiss fighter jet project.
The FFA P-16 was a subsonic strike fighter with a conservative aerodynamic configuration. The aircraft had a low-mounted wing with a slight sweep and wingtip tanks for added range.
Despite efforts from FFA to keep the project alive, the Swiss government canceled their order. The P-16 had met its end, but it had caught the attention of American businessman Bill Lear, who had been interested in creating a business jet.
He founded the Swiss American Aircraft Corporation and formed a team of engineers who had worked with the P-16. Because of administrative problems, SAAC moved to Wichita, Kansas, but continued work on their project.
The Learjet 23 prototype first flew in late 1963, now under the rebranded Lear Jet Corporation, and deliveries began in 1964. The type was a hit among wealthy flyers but had some teething issues. The Learjet team never stopped working on the jet, and in 1966 they oversaw the first flight and delivery of the improved Learjet 24.
Learjet 24 / Specs
The Learjet 24 is a high-speed business jet that seats up to six passengers in addition to the crew. It shares multiple aspects with the Learjet 23. Model 24 meets FAR-25 standards.
FAR-25 regulates the airworthiness of transport aircraft and requires more redundancies and safety features than jets in the utility category. Without this certification, the Learjet 23 could not exceed a maximum takeoff weight of 12500 lbs.
Despite being externally like the Model 23, the new aircraft had many improvements. Each engine had a fire-extinguishing system installed and was more powerful.
The cabin had better pressurization for higher service ceilings, an additional passenger window on the starboard side, and a redesigned windshield. The fuel capacity of the wingtip tanks grew as well. The Model 24 was the first business jet to earn its FAR-25 certification in 1966.
By choosing the transport certificate, Learjet did away with the single-pilot capability present on Model 23. Besides the crew, the Learjet 24 could take between four and six passengers depending on the cabin layout.
The wing of the Learjet 24 closely resembled that of the P-16. The aircraft had a wing area of 231.77 sq ft and an aspect ratio of 5.01 to 1.
The engineering team used the NACA 64A109 airfoil in the project. The Learjet 24 had a wingspan of 35 ft 7 with the tip tanks. The top of the tail sits 12 ft 3 from the ground, and the aircraft is 43 ft 3 long. In 1976, Learjet introduced the Model 24E and Model 24F, with a redesigned wing branded Century III to improve stall performance and approach speeds.
The Learjet 24 has an empty weight of 7130 lbs and a maximum takeoff weight (MTOW) of 13500 lbs because of the FAR-25 certification. The Learjet 24 family had a fuel capacity of 840 US gallons, except for the Model 24E. This model replaced one of the fuselage fuel tanks, allowing operators to fly with higher useful payloads at the expense of maximum range.
Because of the high fuel capacity of the wingtip tanks, refueling the Learjet 24 was an awkward affair. The jet had no single-point fuel plug, so ground crews had to fuel them individually. If an inexperienced person tried to fill in a tip tank in one go, it could cause the aircraft to tip over.
The most common procedure was adding 125 gallons on one side and then 250 gals on the opposite, alternating between the tanks until both were full. The wingtip tanks have fuel pumps installed, but they are capable of gravity feed halfway down to their capacity in case all the pumps fail.
Power comes from a pair of General Electric CJ610 single-rotor turbojet engines. Most Model 24 aircraft came with the CJ610-6, which outputs 2950 lbf of thrust at sea level.
The Learjet 24E and 24F used the CJ610-8A, with the same power rating but lower fuel consumption. This powerplant was a non-afterburning modification of the military General Electric J85 that equipped the F-5, T-38, and A-37 in service with the US Air Force.
The engine RPM gauge indicated a percentage of the maximum angular speed in 2% intervals, with a smaller dial for values from 0 to 10% for increased accuracy.
For convenience and higher consistency across different atmospheric conditions, the Learjet 24 had an engine pressure ratio gauge. To attain performance profiles, the pilots could set the appropriate pressure ratio with the throttles.
The engines also drove pumps to provide hydraulic power to the aircraft, with a nominal pressure between 1250 to 1500 psi. The auxiliary aerodynamic surfaces plus the brakes on the Learjet 24 draw from the hydraulic system.
The main landing gear legs have two wheels each, with a single steerable nose wheel connected to the rudder pedals. In case of hydraulic or electric failure, the aircraft’s pneumatic system can deploy the landing gear.
The Learjet 24 has no thrust reverser and relies on hydraulically boosted brakes to shorten its landing run. The aircraft has an anti-skid braking system to improve stopping distances.
The Learjet 24 series uses cables for the flight controls, making it fully controllable regardless of failures.
Learjet 24 / Prices
During its production run, the Learjet 24 had the distinction of being the fastest and one of the cheapest business jets in the market. The flyaway cost for a Model 24 in 1970 was $989000.
Learjet 24 / Performance and Handling
The Learjet 24F has a top speed of 474 knots at 31000 ft, with a nominal maximum Mach number of 0.86.
The aircraft manual recommends an economical cruising profile of 418 knots at 45000 ft, the original service ceiling. In 1977, the Federal Aviation Agency revised this limit to 51000 ft. With four passengers, two crew, and a full fuel load, the Model 24F has a range of 1473 nautical miles, plus 45 minutes of reserves.
The Learjet 24 was unusually fast at its introduction, with a climb rate of 6800 feet per minute. Pilots coming from other types sometimes have difficulty coping with the awe-inspiring performance of the Learjet. Events during flight develop much faster than they are used to, particularly during the takeoff and climb.
Unlike contemporary Cessna Citation models that flew a step-climb, the Learjet 24 likes to soar to cruise altitude in one go. The time from takeoff to 41000 ft is a mere 12 minutes.
Controls on the Learjet are more responsive than most business jets. When hand-flying the aircraft, a minor unintended pitch input sends the aircraft hundreds of feet off the designated altitude. Pilot and aviation writer Budd Davidson described the aileron controls as “fairly light”.
Turn coordination is automatic in the Model 24 because of a yaw damper system. Below 130 knots, earlier Learjet 24 variants have a slight tendency to Dutch roll. Experienced pilots limit aileron inputs during landing for this reason.
Thanks to the redesigned Century III wing, the Model 24 has a stall airspeed of 87 knots with landing flaps and gear deployed. These speeds reduced the required landing run to 2450 ft, with a takeoff length of 2800 ft.
The aircraft boasts good throttle responsiveness at low speeds. Controlling altitude and airspeed in the approach phase is very comfortable.
Like most T-tail designs, the Learjet 24 can fall into a deep stall. The yoke comes with a stick shaker device that prevents the aircraft from entering unrecoverable situations. It can push the nose down before stalling and pull up to prevent overspeeding. If the flight data computer detects excessive G-loads, the stick shaker brings the yoke closer to a neutral position.
Learjet 24 / Maintenance Schedule
Pilots and owners love the Learjet 24 for its reliability. This light jet boasts low abort rates, and many operators feel confident using it for time-sensitive services like air ambulance flights. So long as parts are available, the Model 24 can fly happily.
Guaranteeing this supply of spare parts has been difficult, which is why many operators have sold their Learjet 24 fleet in exchange for younger Learjet models.
Learjet 24 / Modifications and Upgrades
Learjet built the Model 24 in five variants, with production spanning from 1966 to 1977.
The first version of the Learjet 24 was the Model 24A. The defining member of the family required a pilot and co-pilot because of the FAR-25 certificate, a service ceiling of 41000 ft, and a takeoff weight of 13499 lbs. Learjet built 81 Model 24A units before production switched to the Model 24B in 1969.
The Model 24B improved the original Learjet 24 by replacing the engines with an improved CJ610-6 variant. Learjet produced the Model 24B between 1969 and 1971.
In 1970, Learjet attempted to lighten the empty weight of the Model 24B to allow for higher payloads. Most of the work on the Model 24C focused on removing the fuselage tank. While this change achieved the design goals, the loss of range was deemed unacceptable. Learjet canceled the Model 24C in 1970 but introduced the Model 24D in the same year.
The new aircraft redesigned wing and fuselage fuel tanks which helped lower its weight while extending its range. The Model 24D had a maximum takeoff weight of 13512 lbs. Learjet built 99 units between 1970 and 1976.
Model 24E and Model 24F
The Learjet 24 already boasted marvelous runway and approach performance, but many pilots and operators complained about handling at low speeds.
The Model 24 had tight stall margins that made landings tenser than some would like, particularly in shorter fields. In 1976, Learjet made the first significant attempt to remedy this with the Century III wing. The new wing reduced both stall and approach speeds, allowing the Learjet 24 to land in short fields without a worry in the cockpit.
Learjet replaced the CJ610-6 turbojet with the new CJ610-8A variant. The engines had a similar thrust rating to its predecessor, with improved fuel consumption, durability, and high-altitude performance.
Learjet marketed their revised aircraft as the Model 24E and Model 24F. The two jets were identical, except the Model 24E did not have the fuselage fuel tank fitted in the factory.
Many operators reversed this change. In 1977, the Federal Aviation Agency approved a new service ceiling of 51000 ft for the new Learjet 24, the highest of any business jet then. Learjet produced the Model 24E and Model 24F between 1976 and 1977, with only 29 units.
Learjet 24 / Where to Find Replacement Parts
At the height of its popularity, the Learjet 24 was a common sight. This private jet family can find certified part shops and suppliers almost anywhere, but that is only half the story.
The Learjet family underwent many changes since its inception in 1963 before meeting its end in 2021 when Canadian aerospace giant Bombardier discontinued the line permanently.
The production of most Learjet spare parts ended years ago, and the problem affects older variants like the Model 24 even harder. Learjet 24 operators must constantly scout the market for components to keep the aircraft airworthy.
Learjet 24 / Common Problems
Most problems with the Learjet 24 come from its advanced age. It is increasingly hard to find spare parts for the jets quickly. The situation is approaching a critical point, and some owners are purchasing Model 24 airframes to sit in the hangar as spare parts sources.
The Learjet 24 predates the modern glass cockpits and digital avionics that are standard today. The jet has kilometers of cables running through it, and replacements are inevitable. This type of work is both costly and time-consuming.
The CJ610 engines are excellent turbojets, boasting good reliability, throttle response, and consumption at cruise altitudes. However, they do not comply with Stage 3 requirements outlined by the Noise Control Act of 1972. Hush kits are necessary to fly a Learjet 24 anywhere in the continental United States.
The European Union enforces similar regulations. The consumption of the CJ610 at lower altitudes is dramatically higher than that at the service ceiling. It makes routine events like a long hold or a missed approach more stressful than they must be during long trips.
Like most of the classic Learjet variants, the Model 24 sits very close to the ground. The sight picture in the flare is unusual compared to most aircraft, so inexperienced pilots pull the throttles higher than they should. The problem usually goes away after a pair of educational hard landings.
Learjet 24 / Insurance Options
According to Conklin & de Decker Research, the Learjet 24 costs $19400 to insure on average, assuming a crew with moderate experience in this aircraft class and at least some hours aboard the Learjet 24 family. This figure covers $2900 for hull insurance and $16500 for liability insurance.
Learjet 24 / Resale Value
According to data from International Aviation HQ, Learjet 24 prices are constantly dwindling. Most marketplace offers range from $350000 down to as little as $100000, making them some of the cheapest business jets in the market.
The modern aviation environment keeps Model 24 prices low. Like any older airframe, parts availability becomes worse with every year. The engines are a source of trouble. Without modifications, Learjet 24 does not comply with Stage 3 requirements. As with most turbojet engines, the fuel consumption is far higher than the turbofans on later Learjet models.
Learjet 24 / Owner Reviews
Learjet 24 pilots and passengers love the pressurization system. Cabin pressure remains steady at both maximum performance climbs and steep descents at Vne. This pressurization system is a welcome feature for an aircraft famous for its blistering vertical performance.
Many pilots find the instrument panel crowded compared to other business jets from the 1970s and 1980s. Learjet placed the essential instruments behind the yoke but peppered the rest of the dashboard with auxiliary indicators.
Because of the real estate limitations, the engine instruments are all small and occupy two narrow columns in the middle of the panel. Pilots with US Air Force experience will recognize some of the engine dials from the venerable T-38 Talon supersonic trainer.
Learjet 24 / Similar Aircraft
In the 1960s, the Learjet 24 faced stiff competition from the North American Sabreliner. The Sabreliner used a pair of Pratt & Whitney J60 or JT12 turbojet engines and shared a design peculiarity with the Model 24.
While the Learjet family got its wings from the FFA P-16 fighter, the Sabreliner drew inspiration from the North American iconic F-86 Sabre, most famous for its performance in the Korean War against the venerable MiG-15.
This peculiarity makes the Sabrejet authorized for aerobatics up to 3G. The Sabreliner still flies with militaries worldwide as an advanced trainer for pilots, navigators, and systems officers.
In 1969, Cessna introduced the five-seat Citation I to the market. The aircraft was cheaper and easier to fly than the Learjet 24, but many operators found its performance underwhelming.
The same straight wing that made the Citation I docile across the envelope severely limited its top speed. The engines had low fuel consumption but also outputted little power in return. The Citation I made sense for owners interested in short hops, but it could never compete with the Learjet 24 in longer routes.
Today, one of the main competitors of the Learjet 24 is the Eclipse 500 and 550. Eclipse Aviation introduced this light jet in 2006 and produced a whopping 260 of them before production shifted to the Eclipse 550 in 2013.
The parent company filed for bankruptcy in 2021, but there are 293 such jets flying today. The Eclipse had turbulent infancy, but after some work, it became cheap, reliable, and exciting to fly and own.
Learjet 24 / Clubs You Can Join
Type clubs for business jets are hard to come by, but the popularity of the classic Learjet models like the Model 24 makes it easy to find pilots and owners acquainted with the type in FBOs.
Question: Is the Learjet 24 single-pilot?
Answer: No. While the Learjet 23 requires a single pilot, Learjet did away with this capability in exchange for meeting FAR-25 requirements.
Question: How Much is a Learjet 24?
Answer: A Learjet 24 can cost up to $350 thousand. Learjet sold new airframes for $989000 in 1970.
Question: Can a Learjet 24 do Aerobatics?
Answer: Yes! In the United States, the Clay Lacy Learjet 24 flies an incredible aerobatic routine at airshows.
Question: Does the Learjet 24 Have Single-Point Refueling?
Answer: No. Refueling the Learjet 24 is a time-consuming affair that involves balancing the tip tanks to prevent them from unsettling the aircraft.
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