CFM International CFM56: Wikis


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An exposed jet engine at a trade show. The rear of the polished metal fan case is visible on the left. The outer casing of the compressor section, covered in fuel lines and electrical wires is in to the right of the fan case. The right of the image shows the back of the engine, the exhaust area of the turbine section.
Rear view of CFM56-5
Type Turbofan
National origin France and United States
Manufacturer CFM International
First run June 1974
Major applications Airbus A320 family
Airbus A340
Boeing 737
KC-135R Stratotanker
Number built ~20,000 (as of Sep 2009)
Developed from General Electric F101
Developed into CFM International LEAP-X

The CFM International CFM56 (US military designation F108) series are a family of high-bypass turbofan engines made by CFM International with a thrust range from 18,500 to 34,000 pounds-force (82 to 151 kilonewtons). CFM International is a 50-50 joint company of SNECMA, France and GE Aviation, USA. Both companies are responsible for producing various components and each has their own final assembly line. GE is responsible for the high pressure compressor, combustor and high pressure turbine, and SNECMA is responsible for the fan, low pressure turbine, the gearbox and the exhaust. The engines are assembled by GE in Evendale, Ohio, USA and by SNECMA in Villaroche, France. The completed engines are marketed and sold by CFM International.

The CFM56 first ran in 1974[1] and, despite enduring a difficult and politically charged beginning, is now one of the most prolific engine types in the world with nearly 20,000 built.[2] There are four major variants of the engine, and it is most widely used on the Boeing 737. It is also the sole powerplant of the A340-200/-300, and the CFM56 (designated F108) replaced the Pratt & Whitney JT3D engines on the US KC-135 Stratotanker in the 1980s to create the KC-135R. The engine is also used on some Airbus A320s.

Although the CFM56 is a reliable engine, several fan blade failures were experienced during its early service, one failure was noted as a cause of the Kegworth air disaster. Variants of the engine experienced problems caused by flight through rain and hail. Both of these issues were resolved with engine modifications. By September 2009, the CFM56 had flown over 450 million cumulative hours (the equivalent of more than 51,000 years).[2]


In the late 1960s, it was becoming clear that the the next generation of commercial engines would be high bypass ratio engines in the "10-ton" (20,000 lbf; 89 kN) class. SNECMA was the first to act, and began searching for a partner with commercial experience (they had mostly built military engines to this point) to design and build the engine. After considering Pratt & Whitney, Rolls-Royce, and GE Aviation, SNECMA selected GE. The two main reasons GE was likely selected was that they needed an engine in this market class (Pratt & Whitney dominated the commercial market at this point), and that SNECMA had experience with them, collaborating on the production of the CF6-50 turbofan for the Airbus A300.[1]

A major reason that GE was so interested in the collaborative project, rather than building a 10-ton engine on their own, was that the SNECMA project was the only source for development funds for an engine in this class at the time. GE was initially considering only contributing technology from its CF6 engine rather than its much more advanced F101 engine, developed for the B-1 Lancer supersonic bomber. However the US Air Force announced its Advanced Medium STOL Transport (AMST) project in 1972 which included funding for the development of a 10-ton engine. GE was now faced with a dilemma—should they build two 10-ton engines, one with "limited" technology with SNECMA and one with "advanced" technology on their own, or should they try to develop a single, advanced, engine? Worried that if they did not win the Air Force contract with the advanced engine (in which they were competing with Pratt & Whitney and GM), they would be left with only the "limited" engine in their portfolio, GE decided to apply for an export license for the F101 core technology.[3]

Export issues

In 1972, GE applied for an export license for its F101 core technology as GE's primary contribution to the "10-ton" engine project. However, the United States Department of State's Office of Munitions Control recommended the rejection of the application on national security grounds, specifically because the core technology was an aspect of a strategic national defense system (the B-1 bomber), it was built with Department of Defense (and therefore American taxpayer) money, and that exporting the technology to France would limit the number of American workers on the project.[4] The official decision was made in a National Security Decision Memorandum signed by the National Security Advisor Henry Kissinger on 19 September 1972.[5]

While national security concerns were cited as the grounds for the rejection, it was reported that high-level politics played an important role as well. The project, and the export issue associated with it, was considered so important that French President Georges Pompidou appealed directly to President Richard Nixon in 1971 to approve the deal, and that Henry Kissinger brought the issue up with President Pompidou in a 1972 meeting. GE reportedly argued at the highest levels that having half of the market was better than having none of it, which they argued would happen if SNECMA pursued the engine on their own without GE's contribution. However, Nixon administration officials feared that this project could be the beginning of the end of American aerospace leadership.[6]

There was also speculation that the rejection may have been, in part, retaliation for French involvement in convincing the Swiss not to purchase American-made A-7 Corsair II aircraft that had been competing against a French design (in the end the Swiss decided not to buy either of the aircraft).[6]

1973 Nixon/Pompidou meeting

Two men in suits stand to the right, with uniformed military officers nearby. Both men have their hands raised, waving to an unseen audience.
US President Nixon and French President George Pompidou prior to the 1973 US-French summit in Reykjavik, Iceland.

Despite the export license being rejected, both the French and GE continued to push the Nixon Administration for permission to export the F101 technology. Efforts continued throughout the months following the rejection, culminating in the engine being an agenda topic during the 1973 meeting of Presidents Nixon and Pompidou in Reykjavik. Discussions at this meeting resulted in an agreement, allowing the development of the CFM56 to proceed. At the time it was reported that the agreement was based around assurances that the core of the engine, the part GE was developing from the military F101, would be built in the United States and then transported to France in order to protect the sensitive technologies.[7] In addition, documents declassified in 2007 revealed that a key aspect of the CFM56 export agreement was that French government agreed not seek tariffs against American aircraft being imported into Europe.[8]

CFM International

With the export issue now settled, GE and SNECMA worked out the agreement that founded CFM International (CFMI), which was the 50-50 joint venture that would be responsible for producing and marketing the 10-ton engine, the CFM56. The venture was officially founded in 1974.[9] The two primary roles for CFMI were to manage the program between GE and SNECMA and to market/sell/service the engine at a single point of contact for the customer. CMFI was responsible for the day-to-day decision making for the project, while major decisions (developing a new variant, for example) required the go-ahead from GE and SNECMA management.[1]

The CFMI Board of Directors is split evenly between SNECMA and GE (five members each). There are two Vice Presidents, one from each company, who support the President of CFMI. The President tends to be drawn from SNECMA and sits at CFMI's headquarters near GE in Cincinnati, Ohio.[1]

The work split between the two companies gave GE responsibility for the high pressure compressor (HPC), the combustor, and the high pressure turbine (HPT), while SNECMA was responsible for the fan, the low pressure compressor (LPC), and the low pressure turbine (LPT).[10] SNECMA was also responsible for the initial airframe integration engineering, mostly involving the nacelle design. SNECMA was initially responsible for the gearbox, but shifted that work to GE when it became apparent that it would be more efficient for GE to assemble that component along with their other parts.[11]

Early development

Once the export agreement was settled, development work on the CFM56 began in earnest, even before CFM International was formally created. While most work proceeded smoothly, the international arrangement led to unique working conditions. For example, both companies had assembly lines, so some of the engines were assembled and tested in the US, and some were assembled and tested in France. Those engines assembled in France had to work around the initially strict export agreement, which meant GE's core was built in the US, then shipped to the SNECMA plant in France, and then placed in a locked room that the President of SNECMA was not even allowed in. The SNECMA components (the fore and aft sections of the engine) are brought into the room, where GE employees mounted them to the core. Then the assembled engine is taken out to be finished.[12]

Despite challenges like this, work on the first CFM56 engine proceeded, and first ran at GE in June 1974. The second engine also first ran at GE in October 1974. It was then shipped to France in December, and first ran there on December 13, 1974. These first CFM56 engines were considered "production hardware", not just test articles, and were designated as CFM56-2 engines, which was the first variant of the CFM56.[11]

Three years later, in February 1977, the engine flew for the firs time on the McDonnell Douglas YC-15, an entrant in the Air Force's Advanced Medium STOL Transport (AMST) competition. It replaced one of the aircraft's four Pratt & Whitney JT8D engines.[13] Soon after the engine first flew on the YC-15, the next CFM56 was mounted on a Sud Aviation Caravelle at the SNECMA flight test center in France. This engine had a slightly different configuration with a long bypass duct with mixed exhaust flow,[nb 1] rather than a short bypass duct with unmixed exhaust flow.[nb 2] It was the first to include a "Thrust Management System" to maintain engine trim.[nb 3][14]

First customers

After testing the engine for several years, both in the air and on the ground, CFM International was looking for customers outside of a possible AMST contract. The main targets were re-engine contracts for the Douglas DC-8 and the Boeing 707, including the related military tanker, the KC-135 Stratotanker. After announcing that a 707 would be configured with the CFM56 engine for flight tests in 1977, Boeing officially offered the 707-320 with the CFM56 engine as an option in 1978.[15] Having the commercial 707 available with the CFM56 helped the engine's competitiveness for the KC-135 re-engine contract.[16]

A gray aircraft faces the left of the image, shown from the bottom. Four engines are visible hanging in their nacelles on the underside of the wing.
An air-to-air view of a re-engined KC-135R on its maiden flight. The new engines are CFM56-2 high bypass turbofans.

Winning the contract to re-engine the KC-135 tanker fleet for the US Air Force would be a huge boon to the CFM56 project (with 600+ aircraft available to re-engine), and CFM International aggressively pursued that goal as soon as the Request For Proposals (RFP) was announced in 1977. Like other aspects of the program, international politics played their in this contract. In efforts to boost the CFM56's chances versus its competitors (the Pratt & Whitney TF33 and an updated Pratt & Whitney JT8D), the French government announced in 1978 that they would upgrade their 11 KC-135s with the CFM56 engine. Whatever the impetus for the French announcement, it was one of the first orders for the CFM56 engine.[17]

The USAF announced the CFM56 as the winner of the re-engine contract in early 1980. Officials indicated that they were excited to replace the Pratt & Whitney J57 engines currently flying on the KC-135A aircraft, calling them "...the noisiest, dirtiest, [and] most fuel inefficient powerplant still flying" at the time.[18] The re-engined KC-135 was designated the KC-135R. The CFM56 brought many benefits to the KC-135, decreasing takeoff roll by as much as 3,500 ft (1,100 m), decreasing overall fuel usage by 25%, greatly reducing noise (24 dB lower), and lowering total life cycle cost. With those benefits in mind, the United States Navy selected the CFM56-2 to power their variant of the the Boeing 707, the E-6 Mercury.[16]


By the end of the 1970s, airlines were considering upgrading their aging Douglas DC-8 aircraft as an alternative to buying new quieter and more efficient aircraft. After the French KC-135 announcement in 1978, the April 1979 decision by United Airlines to upgrade 30 of their DC-8-61 aircraft with the CFM56-2 was important for the CFM56.[19] That decision marked the first commercial purchase (rather than government/military) of the engine, and Delta Air Lines and Flying Tiger Line soon followed suit, giving the CFM56 firm footing in both the military and commercial realms.[1]

Boeing 737
A zoomed in view of the front of an engine nacelle. The fan blades of the engine are in the middle of the image. They are surrounded by the engine nacelle, which is seemingly circular on the top half, and flattened on the bottom half.
Engine inlet of a Garuda Indonesia Boeing 737-400 series showing the non-circular inlet for the CFM56 engine.

In what was likely the most important early purchase for the CFM56, Boeing selected the CFM56-3 to exclusively power the latest Boeing 737, the 737-300, in the early 1980s. The small launch order for the 737-300, only 20 aircraft between two airlines, did little to foreshadow the success the aircraft and engine were going to have.[1] The 737 had lower wings than the previous applications for the CFM56, so several modifications had to be made to the engine. The fan diameter was reduced, which reduced the bypass ratio. Additionally, the engine accessory gearbox was moved from the bottom of the engine (the 6 o'clock position) to the 9 o'clock position, giving the the engine nacelle its distinctive flat-bottomed shape. The overall thrust was also reduced, from 24,000 to 20,000 lbf (110 to 89 kN), mostly due to the reduction in bypass ratio.[20]

Continued development

Once the CFM56 was well established in both military and commercial applications, CFM International continued to improve the engine and market it for new aircraft, like the Airbus A320 and the Airbus A340. As of 2009, there are 6 major variants of the engine, each with multiple sub-variants. (Details described below in the "Variants" section).


The CFM56 is a high-bypass turbofan engine with several variants generating a wide range of thrust, from 18,500 to 34,000 lbf (82 kN to 151 kN). The variants share a common design, but the details differ. The CFM56 is a two-shaft (or two-spool) engine, meaning that there are two rotating shafts, one high-pressure and one low-pressure. Each is powered by its own turbine section (the high-pressure and low-pressure turbines, respectively). The fan and booster (low pressure compressor) evolved over the different iterations of engine, as did the compressor, combustor, and turbine sections.[1]

Fan and booster

The front fan of a jet engine facing the left of the image, surrounded by its metal casing. The conical inlet in seen right in front of the metal fan blades. The fan casing is seen in three distinct (but attached) sections from left to right, first a silver-colored section, then a golden-colored section, then another silver-colored section.
View of the CFM56-5 front fan and fan case

The CFM56 features a single-stage fan and either a 3- or 4-stage booster (depending on variant) on the low-pressure shaft.[nb 4] The booster is also commonly called the "low-pressure compressor" (LPC), as it sits on the low-pressure shaft and compresses the flow initially before reaching the high-pressure compressor. The original CFM56 variant, the -2, featured 44 tip-shrouded fan blades,[21] although the number of fan blades dropped in later variants as wide-chord blade technology developed, down to 24 blades in the latest variant, the CFM56-7B.[22]

The fan diameter varies with the different models of the CFM56, and that change has a direct impact on the engine performance. For example, the low-pressure shaft rotates at the same speed for both the CFM56-2 and the CFM56-3 models. However, the fan diameter is smaller on the -3, which lowers the tip speed of the fan blades. The lower speed allows the fan blades to operate more efficiently (5.5% more in this case), which increased the overall fuel efficiency of the engine (improving specific fuel consumption nearly 3%).[20]

The CFM56's bypass ratio ranges from 5:1 to 6:1 depending on variant, the majority of the air accelerated by the fan bypasses the core of engine and is exhausted out of the fan case. The air that does go through the core is first compressed by the booster (or low pressure compressor) before reaching the high pressure compressor. In most variants of the CFM56, the booster consists of three stages. In the -5B and -5C variants, the booster has four stages.[23]


An engine is shown on a display stand at a museum, with the front of the engine facing left. Sections of the casing are cut away and replaced with clear plastic, revealing the booster blades, the compressor blades, and the turbine blades, from left to right.
View of an opened CFM56-3 engine, focused at the high pressure compressor.

The high-pressure compressor (HPC) in all variants of the CFM56 features 9 stages. As the design developed, the HPC was improved, mostly through better blade design. In 2007, CFM International offered an upgraded HPC, again improved with better blade aerodynamics, as a part of their "Tech Insertion" package.[24]


Most variants of the CFM56 features a single-annular combustor. An annular combustor is a continuous ring where fuel is injected into the airflow and ignited, raising the pressure and temperature of the flow. Other types of combustors include "can" combustors, where each combustion chamber is separate, and "can-annular", which is a hybrid of the two.

In 1989, CFM International began work on a new, double-annular, combustor. Instead of having just one combustion zone, the double-annular combustor has a second combustion zone that is used at high thrust levels. This combustor lowers both nitrogen oxides (NOx) and carbon dioxide (CO2) emissions. The first CFM56 engine with the double-annular combustor went into service in 1995, and the combustor is used on "Tech Insertion" CFM56-5B and CFM56-7B variants.[25]

Recently, GE has been testing a new type of combustor called the Twin Annular Premixing Swirler Combustor, or "TAPS". This combustor is similar to the double-annular combustor in that it has two combustion zones. However, this combustor "swirls" the flow, creating an ideal fuel-air mixture. This difference allows the combustor to generate much less NOx than other combustors. Tests on a CFM56-7B engine demonstrated an improvement of 46% over single-annular combustors and an improvement of 22% over double-annular combustors.[26]

Some of the analytical tools developed for TAPS were also used to improve the single-annular combustors in some CFM56-5B and -7B engines.[27]


All variants of the CFM56 feature a single-stage high-pressure turbine (HPT). In some variants, the HPT blades are "grown" from a single crystal, giving them high strength and creep resistance. The low pressure turbine (LPT) features four stages in most variants of the engine, but the CFM56-5C has a five stage LPT. This change was implemented to drive the larger fan on this variant.[28]


Although CFM International tested both a mixed and unmixed exhaust design at the beginning of development,[1] most variants of the engine feature an unmixed exhaust[nb 2] nozzle. Only the high power CFM56-5C, designed for the Airbus A340 has a mixed flow exhaust[nb 1] nozzle.[28]

Additionally, GE and SNECMA tested the effectiveness of chevrons[nb 5] on reducing jet noise. After examining configurations in the wind tunnel, CFM International chose to flight test chevrons built into the core exhaust nozzle. The chevrons reduced jet noise by 1.3 perceived loudness decibels during takeoff conditions. The chevrons are now offered as an option with the CFM56 for the Airbus A321.[29]

Engine failures

Although the CFM56 is a very reliable engine (CFM International state that there is only one in-flight shutdown every 333,333 hours),[30] there have been several engine failures throughout the life of the CFM56 family which were serious enough to either ground the fleet or require aspects of the engine to be redesigned.

Fan blade failure

One issue that led to accidents with the CFM56-3 engine was the failure of a fan blade. This sort of failure led to the Kegworth air disaster in 1989, which killed 47 people and injured 74 more. After the fan blade had failed, the pilots mistakenly shut down the wrong engine, resulting in the entire engine failing when powered up after descent. After the Kegworth accident, two other CFM56 engines suffered fan blade failures under similar conditions (a Dan-Air 737-400 and a British Midland 737-400; neither incident resulted in a crash or injuries).[31] After the second incident, the 737-400 fleet was grounded. Analysis revealed that the fan was being subjected to vibrations that were worse than expected and more severe than tested for certification. The certification testing failed to reveal vibration modes that the fan experienced during power climbs at high altitude (most testing is performed at sea level). As these types of climbs are performed regularly, the fan blades were being subjected to high cycle fatigue stresses that were worse than expected, causing the blade to fracture. Less than a month after grounding, the fleet was allowed to resume operations once the fan blades and fan disc were replaced and the electronic engine controls were modified to reduce maximum engine thrust to 22,000 lbf (98 kN) from 23,500 lbf (105 kN).[32]

Rain/hail ingestion

There are several recorded incidents of CFM56 engines flaming out in heavy rain and/or hail conditions, including the 2002 Garuda Indonesia Flight 421 accident that resulted in the aircraft ditching into a river, killing a flight attendant and injuring dozens of passengers. Prior to this accident, there were several other incidents of the single or dual flame-outs due to these weather conditions. After three incidents through 1998, CFM International made modifications to the engine to improve how the engine handled hail ingestion. The major changes included a modification to the fan/booster splitter (making it more difficult for hail to be ingested by the core of the engine) and the use of an elliptical, rather than conical, spinner at the intake. While these changes did not prevent the 2002 accident, the investigation board found that the pilots did not follow the proper procedures for attempting to restart the engine, which contributed to the final result. Recommendations were made to better educate pilots on how to handle these conditions, as well as to revisit FAA rain and hail testing procedures. No further engine modifications were recommended.[33]


CFM56-2 series

This is the original variant of the CFM56. It is most widely used in military applications, where it is known as the F108, specifically in the KC-135, the E-6 Mercury, and some E-3 Sentry aircraft. The CFM56-2 comprises a single stage fan with 44 blades, with a three-stage LP compressor, driven by a four-stage LP turbine, with a nine-stage HP compressor, driven by a single-stage HP turbine. The combustor is annular.[21]

Model Thrust Bypass Ratio Pressure Ratio Dry Weight
CFM56-2-C1 22,000 lbf (98 kN) 6.0 31.3 4,653 lb (2,110 kg)
CFM56-2A-2 (-3) 24,000 lbf (110 kN) 5.9 31.8 4,820 lb (2,190 kg)
CFM56-2B1 22,000 lbf (98 kN) 6.0 30.5 4,671 lb (2,120 kg)

CFM56-3 series

A mostly white aircraft, with blue nacelles and tail, is shown in the air, seemingly approaching a runway for landing. The aircraft is facing the right of the image with its landing gear down. Two engines are seen in their nacelles.
CFM56-3 series engines mounted on a Boeing 737-300 airliner. Note flattening of the nacelle at the bottom of the inlet lip.

The first derivative of the CFM56 series, the CFM56-3 was designed for Boeing 737-300/-400/-500 series aircraft, with static thrust ratings from 18,500 to 23,500 lbf (82.3 to 105 kN). A "cropped fan" derivative of the -2, the -3 engine has a smaller fan diameter at 60 in (1.5 m) but retains the original basic engine layout. The new fan was primarily derived from GE's CF6-80 turbofan, rather than the CFM56-2, and the booster was redesigned to match the new fan.[20]

A significant challenge for this series was the size of the wing-mounted engine for ground clearance. This was partially overcome by mounting the accessories (like the gearbox) at the lower corners rather than the bottom, and flattening the nacelle bottom and intake lip, thus giving a distinctive appearance of the Boeing 737 with CFM56 engines.[34]

Model Thrust Bypass Ratio Pressure Ratio Dry Weight Applications
CFM56-3B-1 20,000 lbf (89 kN) 6.0 27.5 4,276 lb (1,940 kg) Boeing 737-300, Boeing 737-500
CFM56-3B-2 22,000 lbf (98 kN) 5.9 28.8 4,301 lb (1,950 kg) Boeing 737-300, Boeing 737-400
CFM56-3C-1 23,500 lbf (100 kN) 6.0 30.6 4,301 lb (1,950 kg) Boeing 737-300, Boeing 737-400, Boeing 737-500

CFM56-5 series

The CFM56-5 series is designed for the Airbus aircraft. It has a very wide thrust rating of between 22,000 and 34,000 lbf (97.9 and 151 kN). It differs from its Boeing fitted cousins by featuring a Full Authority Digital Engine Controller (FADEC) and incorporating further aerodynamic design improvements It has three distinct sub-variants, the CFM56-5A, CFM56-5B and CFM56-5C. The Airbus designator for aircraft equipped with CFM engines is "1", such as A320-211 or A340-312.

CFM56-5A series

CFM56-5A series is designed to power the short-to-medium range Airbus A320 family, with thrusts between 22,000 and 26,500 lbf (98 kN and 118 kN). This is the initial CFM56-5 series. Its design is derived from the CFM56-2 and CFM56-3 families. Aerodynamic improvements, such as an updated fan, low-pressure compressor, high-pressure compressor, and combustor, make this variant 10-11% more fuel efficient than its predecessors.[35][36]

Model Thrust Bypass Ratio Pressure Ratio Dry Weight Applications
CFM56-5A1 25,000 lbf (111 kN) 6.0 31.3 4,995 lb (2,270 kg) Airbus A320
CFM56-5A3 26,500 lbf (118 kN) 6.0 31.3 4,995 lb (2,270 kg) Airbus A320
CFM56-5A4 22,000 lbf (97.9 kN) 6.2 31.3 4,995 lb (2,270 kg) Airbus A319
CFM56-5A5 23,500 lbf (105 kN) 6.2 31.3 4,995 lb (2,270 kg) Airbus A319
CFM56-5B series
A white aircraft, with "easyJet" painted in orange on the fuselage, is displayed from behind, facing the left of the image. The rear of one of its engine nacelles is visible in the middle of the image.
CFM56-5Bs power all of easyJet's A319s

An improvement of the CFM56-5A series, it was originally designed to power the A321. Today, it can power every model in the A320 family (A318/A319/A320/A321), with a thrust range is between 22,000 and 33,000 lbf (98 kN and 147 kN), and it has superseded the CFM56-5A series. Among the changes from the CFM56-5A is the option of a double-annular combustor that reduces emissions (particularly NOx), a new fan in a longer fan case, and a new low-pressure compressor with a fourth stage (up from three in earlier variants). It is the most numerous engine supplied to Airbus.[23][37]

Model Thrust Bypass Ratio Pressure Ratio Dry Weight Applications
CFM56-5B1 30,000 lbf (130 kN) 5.5 35.4 5,250 lb (2,380 kg) Airbus A321
CFM56-5B2 31,000 lbf (140 kN) 5.5 35.4 5,250 lb (2,380 kg) Airbus A321
CFM56-5B3 33,000 lbf (150 kN) 5.4 35.5 5,250 lb (2,380 kg) Airbus A321
CFM56-5B4 27,000 lbf (120 kN) 5.7 32.6 5,250 lb (2,380 kg) Airbus A320
CFM56-5B5 22,000 lbf (98 kN) 6.0 32.6 5,250 lb (2,380 kg) Airbus A319
CFM56-5B6 23,500 lbf (100 kN) 5.9 32.6 5,250 lb (2,380 kg) Airbus A319
CFM56-5B7 27,000 lbf (120 kN) 5.7 35.5 5,250 lb (2,380 kg) A319, Airbus A319CJ
CFM56-5B8 21,600 lbf (96 kN) 6.0 32.6 5,250 lb (2,380 kg) Airbus A318
CFM56-5B9 23,300 lbf (100 kN) 5.9 32.6 5,250 lb (2,380 kg) Airbus A318
CFM56-5C series

With a thrust rating of between 31,200 and 34,000 lbf (139 kN and 151 kN), CFM56-5C series is the most powerful of the CFM56 family. It powers Airbus' long-range A340-200 and -300 airliners, and entered service in 1993. The major changes are a larger fan, a fifth low-pressure turbine stage, and the same four stage low-pressure compressor found in the -5B variant.[38]

Unlike every other variant of the CFM56, the -5C features a mixed exhaust nozzle,[nb 1] which offers slightly higher efficiency.[28]

Model Thrust Bypass Ratio Pressure Ratio Dry Weight Applications
CFM56-5C2 31,200 lbf (139 kN) 6.6 37.4 8,796 lb (3,990 kg) Airbus A340-200/-300
CFM56-5C3 32,500 lbf (145 kN) 6.5 37.4 8,796 lb (3,990 kg) Airbus A340-200/-300
CFM56-5C4 34,000 lbf (151 kN) 6.4 38.3 8,796 lb (3,990 kg) Airbus A340-200/-300

CFM56-7 series

The CFM56-7 powers the Boeing 737 Next Generation series (737-600/-700/-800/-900). The CFM56-7 is rated with takeoff thrust from 18,500 to 27,300 lbf (82 kN to 121 kN).

It has higher thrust ranges, improved efficiency, and lower maintenance costs than its predecessor, the CFM56-3 series. It incorporates features from the CFM56-5 series such as FADEC, double annular combustor (as an option), and improved internal design. The basic mechanical arrangement is as the -3 series, but all aspects have been aerodynamically improved from the -3 model. For example, the improved wide-chord fan blades allow the overall number of fan blades to be reduced to 24, from 44. Other improvements came from material advances, such as the use of single crystal turbine blades in the high pressure turbine.[39]

The CFM56-7-powered 737 is granted 180-minute Extended-Range, Twin-Engine Operations (ETOPS) approval by the U.S. Federal Aviation Administration. It also powers the military versions of the Next-Generation 737, the C-40 Clipper, the P-8 Poseidon, and Boeing 737 AEW&C.[40]

Model Thrust Bypass Ratio Pressure Ratio Dry Weight Applications
CFM56-7B18 19,500 lbf (86.7 kN) 5.5 32.8 5,216 lb (2,370 kg) Boeing 737-600
CFM56-7B20 20,600 lbf (91.6 kN) 5.5 32.8 5,216 lb (2,370 kg) Boeing 737-600, Boeing 737-700
CFM56-7B22 22,700 lbf (101 kN) 5.3 32.8 5,216 lb (2,370 kg) Boeing 737-600, Boeing 737-700
CFM56-7B24 24,200 lbf (108 kN) 5.3 32.8 5,216 lb (2,370 kg) Boeing 737-700, Boeing 737-800, Boeing 737-900
CFM56-7B26 26,300 lbf (117 kN) 5.1 32.8 5,216 lb (2,370 kg) Boeing 737-700, Boeing 737-800, Boeing 737-900
CFM56-7B27 27,300 lbf (121 kN) 5.1 32.8 5,216 lb (2,370 kg) Boeing 737-800, Boeing 737-900, Boeing Business Jet


Specifications (CFM56-7B18)

Data from CFM International[39]

General characteristics

  • Type: Twin-spool, high bypass turbofan
  • Length: 98.7 in (2.5 m)
  • Diameter: 61 in (1.55 m) (fan)
  • Dry weight: 5,216 lb (2,366 kg) (dry)


  • Compressor: Single-stage fan, 3-stage low pressure compressor, 9-stage high pressure compressor
  • Turbine: Single-stage high pressure turbine, 4-stage low pressure turbine


See also

Related development

Comparable engines

Related lists


  1. ^ a b c Mixed Exhaust Flow is a term used to describe turbofan engines (both low and high bypass) that exhaust both the hot core flow and the cool bypass flow through a single exit nozzle. The core and bypass flow are "mixed".
  2. ^ a b Unmixed Exhaust Flow is a term used to describe turbofan engines (generally only high bypass, but not exclusively) that exhaust their cool bypass air separately from their hot core flow. This is visually distinctive, as you usually see the outer, wider, bypass section end mid-way along the nacelle and the core continue to "stick out". With two separate exhaust points, the flow is "unmixed"
  3. ^ Engine Trim is a term that generally refers to keeping the components of an engine "in sync" with each other. For example, maintain proper engine trim could mean adjusting the airflow to keep the proper amount of air flowing through the high pressure compressor for a particular flight condition.
  4. ^ The Low Pressure Shaft, in a two-shaft (or two-spool) engine, is the shaft that is turned by the low-pressure turbine (LPT). Generally the fan section(s) and the booster section(s) (also known as the "low-pressure compressor") are on the low-pressure shaft.
  5. ^ Chevron is the name given to sawtooth cutouts that are sometime applied to the exhaust nozzles of jet engines in order to reduce the jet noise. An example can be seen here. (Note that the pictured engine is not a CFM56.)


  1. ^ a b c d e f g h Bilien, J. and Matta, R. (1989). The CFM56 Venture. AIAA/AHS/ASEE Aircraft Design, Systems, and Operations Conference. Seattle, WA, 31 July - 2 Aug. 1989. AIAA-89-2038
  2. ^ a b Fleet Statistics. CFM International Website. Accessed: 17 November 2009.
  3. ^ Samuelson, Robert (1972). Commerce, Security and the "Ten Ton Engine". The Washington Post. 8 October 1972, p. H7.
  4. ^ Farnsworth, Clyde (1973). GE, French To Make Jet Engine. St. Petersburg Times, 23 June 1973, p. 11-A. Accessed: 4 November 2009. Google News Archive.
  5. ^ GE-SNECMA Jet Engine Joint Venture (1972). National Security Decision Memorandum 189. 19 Sept 1972. NSDM 189 (pdf). Accessed: 9 November 2009.
  6. ^ a b "A Rebuff to Pompidou on Engine" (1972). The New York Times. 30 Sept 1972, p. 39.
  7. ^ Farnsworth, Clyde (1973). U.S. Ban Lifted on G. E. Plan. The New York Times. 23 June 1973, p. 37.
  8. ^ GE-SNECMA. CFM-56 Jet Engine Joint Development (1973). National Security Decision Memorandum 220. 4 June 1973. NSDM 220 (pdf). Accessed: 9 November 2009.
  9. ^ CFM Timeline. CFM56 Website. Accessed: 10 November 2009.
  10. ^ Work Split. CFM56 Website. Accessed: 10 November 2009.
  11. ^ a b Yaffee, Michael (1975). Developers Face 1975 CFM56 Decision. Aviation Week & Space Technology. 24 Feb 1975, p. 41.
  12. ^ Lewis, Flora (1975). G.E.-SNECMA Deal: U.S.-French Dispute Is Obscured. The New York Times. 5 Mar 1975, pp 53.
  13. ^ "YC-15 Enters New Flight Test Series". Aviation Week and Space Technology. 21 Feb. 1977, p. 27.
  14. ^ Shivaram, Malur (1988). A SURVEY OF THE FLIGHT TESTING, AND EVALUATION OF CFM56 SERIES TURBOFAN. 4th AIAA Flight Test Conference, San Diego, CA. Technical Papers AIAA-1988-2078.
  15. ^ O'Lone, Richard (1978). Boeing to Offer 707-320 Re-engined with CFM56s. Aviation Week and Space Technology. 14 August 1978, p. 40.
  16. ^ a b Kazin, S (1983). KC-135/CFM56 RE-ENGINE, THE BEST SOLUTION. 19th AIAA/SAE/ASME Joint Propulsion Conference, 27-29 June 1983. Seattle, Washington. AIAA-1983-1374.
  17. ^ GE, French Firm Get Jet Engines Contract. The Wall Street Journal. 8 November 1978, p. 14.
  18. ^ "CFM56 Selected for KC-135 Re-engining". Aviation Week and Space Technology, 28 Jan 1980.
  19. ^ "United Picks CFM56 for DC-8-60s". Aviation Week and Space Technology. 9 Apr 1979, p. 19.
  20. ^ a b c Epstein, N (1981). CFM56-3 High By-Pass Technology for Single Aisle Twins. 1981 AIAA/SAE/ASCE/ATRIF/TRB International Air Transportation Conference, 26-28 May 1981, Atlantic City, New Jersey. AIAA-1981-0808.
  21. ^ a b CFM56-2 Technology. CFM56 Website. Accessed: 13 November 2009.
  22. ^ CFM56-7B Technology. CFM56 Website. Accessed: 13 November 2009.
  23. ^ a b CFM56-5B Technology. CFM56 Website. Accessed: 13 November 2009.
  24. ^ Norris, Guy (2004). "CFMI details insertion plan for Tech 56". Flight International. 3 August 2004. Accessed: 17 November 2009.
  25. ^ "CFM'S Advanced Double Annular Combustor Technology". CFM International Press Release. 9 July 1998. Accessed: 16 November 2009.
  26. ^ Mongia, Hukam (2003). TAPS –A 4th Generation Propulsion Combustor Technology for Low Emissions. AIAA/ICAS International Air and Space Symposium and Exposition: The Next 100 Years, 14-17 July 2003, Dayton, Ohio. AIAA 2003-2657.
  27. ^ CFM56-5B/-7B Tech Insertion Package On Schedule For 2007 EIS. CFM International Press Release. 13 June 2005. Accessed: 16 November 2009.
  28. ^ a b c "CFM56 RISES TO CHALLENGE". Flight International. 11 June 1991. Accessed: 17 November 2009.
  29. ^ Loheac, Pierre, Julliard, Jacques, Dravet, Alain (2004). CFM56 Jet Noise Reduction with the Chevron Nozzle. 10th AIAA/CEAS Aeroacoustics Conference. AIAA 2004-3044
  30. ^ CFM56 Turbofan Engine Reliability. CFM International Website. Accessed: 11 December 2009.
  31. ^ Report on the accident to Boeing 737-400, G-OBME, near Kegworth, Leicestershire on 8 January 1989. Report No: 4/1990. Air Investigations Branch.
  32. ^ "Derating Clears CFM56-3Cs To Fly" (1989). Flight International. July 1, 1989. Accessed: December 11, 2009.
  33. ^ National Transportation Safety Board Safety Recommendation. A05-19 and 20. NTSB Recommendations. Accessed: December 4, 2009.
  34. ^ CFM56-3 Technology. CFM International Website. Accessed: 20 November 2009.
  35. ^ CFM56-5A History. CFM International Website. Accessed: 20 November 2009.
  36. ^ CFM56-5A Technology. CFM International Website. Accessed: 20 November 2009.
  37. ^ CFM56-5B History. CFM International Website. Accessed: 20 November 2009.
  38. ^ CFM56-5C Technology. CFM International Website. Accessed: 23 November 2009.
  39. ^ a b CFM56-7B Technology. CFM International Website. Accessed: 2 November 2009.
  40. ^ CFM56-7B History. CFM International Website. Accessed: 23 November 2009.

External links

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