CFM International CFM56

CFM International CFM56. The CFM56 is a family of high-bypass turbofan aircraft engines produced by the joint venture CFM International between General Electric of the United States and Safran Aircraft Engines of France. It is one of the most successful commercial aircraft engine programs in aviation history, powering a wide range of narrow-body and military aircraft. Its reliability and efficiency have made it a cornerstone of global aviation for decades.

Development and history

The genesis of the CFM56 program emerged in the early 1970s from a strategic partnership between General Electric and the French state-owned engine manufacturer Snecma (now Safran Aircraft Engines). This collaboration, formalized as CFM International in 1974, aimed to create a modern, fuel-efficient engine to compete with established products from Pratt & Whitney and Rolls-Royce. The initial development leveraged core technology from General Electric's F101 military engine used on the Rockwell B-1 Lancer, while Snecma contributed significant expertise in low-pressure systems and fans. The first engine ran in June 1974, with certification achieved in 1979. Early challenges included finding a launch customer, ultimately secured with the re-engining program for the McDonnell Douglas DC-8 Super 70 series and the Boeing KC-135R military tanker.

Design and variants

The CFM56 is a two-spool, axial-flow, high-bypass turbofan engine. Its core design features a single-stage fan, a multi-stage high-pressure compressor driven by a two-stage high-pressure turbine, and a multi-stage low-pressure turbine. The family comprises several major series, each developed for specific airframes. The initial **CFM56-2** powered the McDonnell Douglas DC-8 and Boeing KC-135 Stratotanker. The **CFM56-3** was developed specifically for the Boeing 737 Classic series. The **CFM56-5** series was tailored for the Airbus A320 family and the Airbus A340-200 and Airbus A340-300. The **CFM56-7** became the exclusive powerplant for the Boeing 737 Next Generation family. Each variant incorporated advancements in materials, aerodynamics, and Full Authority Digital Engine Control (FADEC) systems to improve thrust, fuel burn, and emissions.

Operational history

Entering service in 1982 on the McDonnell Douglas DC-8, the CFM56 quickly established a reputation for exceptional reliability and durability. Its adoption on the Boeing 737 Classic and subsequent Boeing 737 Next Generation solidified its position as the dominant engine in the single-aisle market, competing directly with the IAE V2500 on the Airbus A320 family. The engine's success powered the global expansion of low-cost carriers like Southwest Airlines and Ryanair. Military applications, particularly the re-engining of the United States Air Force Boeing KC-135 Stratotanker fleet, demonstrated its versatility and performance. By the 2010s, over 33,000 engines had been delivered, accumulating hundreds of millions of flight hours.

Specifications (CFM56-7)

* **Type:** Twin-spool high-bypass turbofan * **Length:** 2.516 m (99.1 in) * **Fan diameter:** 1.55 m (61 in) * **Bypass ratio:** 5.5:1 * **Overall pressure ratio:** 32.8:1 * **Thrust range:** 19,500 to 26,300 lbf (87 to 117 kN) * **Turbine inlet temperature:** ~1,350 °C * **Dry weight:** 2,360 kg (5,200 lb) * **Fuel type:** Jet A, Jet A-1

Applications

The primary commercial applications include the Boeing 737 Next Generation (all models), the Boeing 737 Classic (-300, -400, -500), the Airbus A320 family (A318, A319, A320, A321), and the Airbus A340-200/Airbus A340-300. It also powered the re-engined McDonnell Douglas DC-8 Super 70 series. Key military applications are the Boeing KC-135 Stratotanker (KC-135R/T models) and the Northrop Grumman E-8 Joint STARS. Several special mission aircraft, such as the Boeing 737 AEW&C used by the Royal Australian Air Force and the Turkish Air Force, are also powered by the CFM56.

Notable incidents and accidents

While renowned for reliability, the engine has been involved in several notable safety events. In 1989, British Midland Flight 092, a Boeing 737-400, crashed near Kegworth following a fan blade failure in a CFM56-3 engine, leading to changes in pilot training and engine inspection protocols. In 1996, a Delta Air Lines Boeing 767 experienced an uncontained failure of a CFM56-3 during ground maintenance at Pensacola International Airport. Uncontained engine failures have also occurred on aircraft operated by Southwest Airlines and American Airlines, including a 2018 incident on Southwest Airlines Flight 1380 that resulted in a passenger fatality. These events have prompted ongoing Federal Aviation Administration and European Union Aviation Safety Agency airworthiness directives.