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CFM International CFM56

CFM International (GE Aviation + Safran Aircraft Engines) · Aircraft Engine · France / USA · Cold War (1970–1991)

CFM International CFM56 — Aircraft Engine
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The CFM International CFM56 is a family of Franco-American high-bypass turbofans built by CFM International (CFMI), a 50/50 joint venture between GE Aerospace of Evendale, Ohio and Safran Aircraft Engines of Villaroche, France. Thrust spans 18,500 to 34,000 lbf, and the CFM56 became the most-produced jet engine in aviation history — more than 33,000 delivered between 1982 and the late-2010s wind-down, with low-rate production continuing for spares and select military programmes. GE builds the high-pressure compressor, combustor, and high-pressure turbine; Safran manufactures the fan, gearbox, exhaust, and low-pressure turbine. Avio of Italy and Honeywell supply additional parts.

Design work began in 1971 to fill the 20,000-lbf class gap between the early Pratt & Whitney JT8D and the larger CF6 widebody engines. Early sales were almost non-existent — U.S. export controls on the GE-supplied F101 core nearly killed the programme before launch. The breakthrough came in 1979 when Douglas selected the CFM56-2 to re-engine the DC-8 Super 70, halving fuel burn versus the JT3D it replaced. The U.S. Air Force followed with the F108 variant for the KC-135R Stratotanker re-engine programme, eventually converting more than 400 KC-135s with sharp gains in offload, runway performance, and noise reduction.

Civil airliner adoption then exploded. The CFM56-3 (20,000-23,500 lbf) launched on the Boeing 737 Classic in 1984, using a smaller 60-inch fan to fit under the 737's low-slung wing. The CFM56-5 series powered the Airbus A320 family from 1988 and the A340-200/-300. The CFM56-7B (61.5-inch fan, 19,500-27,300 lbf) launched on the Boeing 737 Next Generation in 1997 and became the engine of the best-selling single-aisle airliner ever built. F108 military service continued on the E-3 Sentry AWACS and E-6 Mercury TACAMO fleet.

The CFM56 set the design template for modern single-aisle turbofans: bypass ratios of 5-6:1, single-stage fans of 60-72 inches, and a compact two-shaft core that emphasised reliability and parts commonality across thrust ratings. In-service shop-visit intervals stretched past 30,000 flight hours on the CFM56-7B — the highest of any single-aisle engine to that point. By 2026, the global CFM56 fleet had accumulated more than one billion engine flight hours.

CFM International succeeded the CFM56 with the LEAP family from 2016 onward, but new-build CFM56-7B production for the 737NG continued at low rates through 2020 to support Boeing's final NG deliveries. Spares production and overhaul work will sustain the type through the 2040s on the long-life KC-135R and 737NG fleets. The successor LEAP delivers around 15% better fuel burn but inherits the CFM56's parts-sharing philosophy, customer support model, and joint-venture governance.

For Kids — a shorter, friendlier version

The CFM56 is a jet engine made by a team from two countries. An American company called GE and a French company called Safran built it together. They started designing it back in 1971. Today it is the most-produced jet engine in all of aviation history.

More than 33,000 of these engines have been built and delivered. That is a huge number! Each engine pushes a plane forward with a lot of force. The smallest version pushes with 18,500 pounds of thrust. The biggest pushes with 34,000 pounds of thrust.

The two companies split the work. GE makes the inside parts that squeeze and heat the air. Safran makes the big fan at the front and other important parts. A company from Italy and another called Honeywell also help make some pieces.

The CFM56 powers many famous planes. You might have flown on one! It is used on the Boeing 737 and the Airbus A320. It also powers special military planes like the KC-135 tanker and the E-3 Sentry.

One early success came when it was chosen to power the DC-8 Super 70. The new engine used about half the fuel of the old one. That was a huge saving. The engine family is smaller than many people expect for something so powerful and famous.

Fun Facts

  • More than 33,000 CFM56 engines have been built — that is more than any other jet engine ever!
  • The CFM56 is made by a team split between the United States and France.
  • The biggest CFM56 pushes with 34,000 pounds of thrust — faster than most things you can imagine!
  • When fitted to the DC-8 Super 70, the CFM56 used about half the fuel of the engine it replaced.
  • GE makes the hot inner parts, while Safran makes the big front fan — they share the job equally.
  • The CFM56 is smaller than a city bus yet powerful enough to lift a huge passenger jet.
  • Companies in three countries — America, France, and Italy — all help build parts of this engine.
  • The engine has been in production for over 40 years, starting deliveries in 1982.

Kids’ Questions

What planes use the CFM56 engine?

The CFM56 is used on the Boeing 737 and the Airbus A320, which are very common passenger planes. It also powers military aircraft like the KC-135 tanker and the E-3 Sentry spy plane. You have probably flown on a plane with one of these engines!

Who makes the CFM56 engine?

The CFM56 is made by a team called CFM International. It is a partnership between GE from America and Safran from France. Each company makes different parts of the engine and then they put it all together.

Why is the CFM56 so famous?

The CFM56 is famous because more than 33,000 have been built — more than any other jet engine in history. It is also very fuel-efficient, which means planes save money flying with it. Airlines around the world love using it.

When did engineers start working on the CFM56?

Engineers started designing the CFM56 back in 1971. The first engines were delivered to customers in 1982. That means it took over ten years from idea to finished product!

Variants

CFM56-2 (1982)
Original 24,000-lbf class variant. Re-engined the McDonnell Douglas DC-8 Super 70 and powered the U.S. Air Force E-3 Sentry, E-6 Mercury, and KC-135R under the F108 military designation.
CFM56-3 (1984)
Boeing 737 Classic launch variant. 60-inch fan diameter chosen to fit under the 737's short main-gear stance. 18,500-23,500 lbf, powered all 737-300/-400/-500 production.
CFM56-5 (1988)
Airbus single-aisle and four-engine widebody family. CFM56-5A and -5B on A319/A320/A321 (22,000-33,000 lbf); CFM56-5C on A340-200/-300 (31,200-34,000 lbf) with a 72.3-inch fan.
CFM56-7B (1997)
Boeing 737NG (-600/-700/-800/-900) launch engine. 19,500-27,300 lbf, 61-inch fan. The Tech Insertion package from 2007 cut NOx 15% and extended on-wing life past 30,000 hours.
F108-CF-100 (military)
U.S. Air Force designation for CFM56-2B engines re-engining the KC-135R Stratotanker fleet from 1984. Doubled offload and cut takeoff distance by 25% versus the J57 turbojets they replaced.

Notable Operators

Boeing 737 Classic and 737 Next Generation
More than 7,000 737-300/-400/-500 and 737-600/-700/-800/-900 airframes built with CFM56-3 and CFM56-7B engines. Southwest Airlines, Ryanair, American Airlines, United, Delta, Alaska, and hundreds of other carriers fly the type.
Airbus A320ceo family
CFM56-5A and -5B compete with the IAE V2500 on A319/A320/A321 — split roughly 60/40 in CFM's favour across more than 8,000 ceo-family airframes. Major customers include American, easyJet, Lufthansa, Air France, JetBlue, and Frontier.
Airbus A340-200/-300
CFM56-5C exclusively powered the early A340-200/-300 widebodies — 246 built between 1991 and 2008 for Lufthansa, Air France, Cathay Pacific, Virgin Atlantic, and others. Four CFM56s gave the A340-300 an unrefuelled range past 7,400 nm.
KC-135R Stratotanker (USAF)
F108-CF-100 re-engined more than 400 KC-135s from 1984 onward. The conversion remains the largest military re-engine programme ever executed and extended KC-135 service life past 2040.

Frequently Asked Questions

Why is the CFM56 the most-produced jet engine in history?

Three reasons: it launched on the Boeing 737 Classic in 1984 just as global air travel began its 30-year doubling cycle; it picked up the Airbus A320 launch contract in 1988 and never lost a re-competition; and the 737NG kept the line running until 2020. More than 33,000 engines were delivered across single-aisle, widebody, and military applications — roughly double the next-closest contender, the Pratt & Whitney JT8D at 14,750. CFM International publishes annual delivery counts on its programme page.

What is the CFM56's bypass ratio and fan diameter?

The CFM56-3 (737 Classic) used a 60-inch fan and 6.0:1 bypass ratio. The CFM56-5C (A340) ran the largest fan in the family at 72.3 inches with a 6.6:1 bypass ratio. The CFM56-7B (737NG) settled on 61 inches and 5.4:1. These figures sit well below the LEAP successor's 11:1 ratio, but at the CFM56's 1980s launch they were the highest bypass numbers ever fielded on a single-aisle airliner.

How did the F108 re-engine programme change the KC-135?

Swapping the original Pratt & Whitney J57 turbojets for four CFM56-2B-1 engines doubled fuel offload at typical mission radii, cut takeoff roll by around 25%, and reduced cabin noise by 17 dB. The KC-135R variant entered service in 1984 and now flies until at least 2040 — the longest single airframe service life in U.S. Air Force history. The USAF KC-135 fact sheet documents the conversion timeline.

Is the CFM56 still in production?

New-engine production ended around 2020 with the final 737NG deliveries, but CFM International continues to manufacture spares, build replacement modules, and overhaul engines for the in-service fleet. With more than 21,000 CFM56s still flying in 2026, support work will sustain the programme through the 2040s.

How does the CFM56 compare to the JT8D?

The CFM56 is a true high-bypass turbofan (5-6:1) versus the JT8D's low-bypass design (around 1:1). At similar thrust the CFM56 burns roughly 30% less fuel, runs much quieter, and meets modern Stage 4 noise rules. The CFM56-3 replaced the JT8D on the Boeing 737 generation transition from 737-200 to 737-300 in 1984, and the CFM56-2 replaced JT8D-219s on the McDonnell Douglas Super 27 re-engine kits.

What replaces the CFM56?

The CFM LEAP family entered service in 2016. LEAP-1B powers the Boeing 737 MAX, LEAP-1A the Airbus A320neo, and LEAP-1C the COMAC C919. LEAP raises bypass ratio to around 11:1, introduces 3D-woven composite fan blades, and adds ceramic-matrix-composite turbine shrouds for around 15% better fuel burn than the CFM56-7B.

Sources

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