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TINKER HISTORY: CFM International CFM56 (F108) engine

The military derivative of the CFM56 engine is designated F108 and powers U.S. military aircraft such as the KC-135R Stratotanker, RC-135 family of reconnaissance aircraft and the Navy’s E-6B Mercury. (Photo courtesy of Tinker History Office)

The military derivative of the CFM56 engine is designated F108 and powers U.S. military aircraft such as the KC-135R Stratotanker, RC-135 family of reconnaissance aircraft and the Navy’s E-6B Mercury. (Photo courtesy of Tinker History Office)

TINKER AIR FORCE BASE, Okla. --

The CFM International CFM56 engine is a high-bypass, two-shaft turbofan produced by an international consortium made up of General Electric in the United States and Safran Aircraft Engines in France. The CFM56 is the world’s most widely used turbofan in commercial aviation. The CFM56 powers entire lines of commercial jets made by Airbus and Boeing to include the A3XX series and B737 family of aircraft with operators worldwide. The military derivative is designated F108 and powers U.S. military aircraft such as the KC-135R Stratotanker, RC-135 family of reconnaissance aircraft and the Navy’s E-6B Mercury. 

The CFM family of engines feature a large diameter fan at the front, low and high-pressure sections in 12 stages followed by a combustion chamber, a single high-pressure turbine for reduction of the hot gases across four following low-pressure fan sections. The air moving across the final five sections drives disks of blades connected to an internal shaft which helps drive the front fan blade. After moving through the low-pressure fan sections the air is expelled as exhaust gas.  Only about 20 percent of the air flowing through the engine is compressed through the various stages while the remaining percent is directed around the engine core within the cowling, thus the high-bypass name.

The Oklahoma City Air Logistics Center at Tinker Air Force Base assumed responsibility for the F108 engine program in June 1980 in the initial planning stages for the re-engining of the KC-135. The first KC-135s were re-engined in 1984 and are also used on RC-135 reconnaissance aircraft for the Air Force and E-6Bs for the Navy. The Air Force Life Cycle Management Center currently manages 1,920 engines with 1,845 belonging to the Air Force and 75 for the Navy. The AFLCMC has $8.7 billion worth of engines with $622 million spent annually through 120 programmed overhauls. The proposed retirement date for this engine is 2046.

The F108 engine has added reliability and sustainability to a fleet of aging aircraft while lowering the overall operating costs and increasing capability to the warfighter. At any given point in time there are assuredly dozens of CFM56 or military variants in the F108 engines airborne around the world.

Manufacturer: CFM International

Engine type: High-bypass, two-shaft turbofan

Nickname: CFM56

Maximum thrust: 18,500-34,000 depending on the version

In-service dates: 1984-present

Number produced: 30,000+

Tinker connection: Life cycle management office, maintenance, repair and overhaul