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F108 jet engine overhaul expected to save $2 billion, improve fuel efficiency

Tinker jet engine mechanic Craig Richards, of the 546th Propulsion Maintenance Squadron, works on an F108 engine in the F108 Assembly Shop, Bldg. 9001. The powerhouse of the Air Force KC-135 Stratotanker and Navy E-6B is getting attention as proposed upgrades promise to reduce the maintenance price tag, step up fuel efficiency and save money for the two services. (Air Force photo by Margo Wright)

Tinker jet engine mechanic Craig Richards, of the 546th Propulsion Maintenance Squadron, works on an F108 engine in the F108 Assembly Shop, Bldg. 9001. The powerhouse of the Air Force KC-135 Stratotanker and Navy E-6B is getting attention as proposed upgrades promise to reduce the maintenance price tag, step up fuel efficiency and save money for the two services. (Air Force photo by Margo Wright)

TINKER AIR FORCE BASE, Okla. -- The Air Force and the Navy have teamed up to develop a propulsion upgrade that will keep aircraft vital to both flying longer and at less cost.

The two services worked with private industry to upgrade the F108 (CFM56-2) turbofan jet engine, which is used in Air Force KC-135 Stratotankers and the Navy's E-6B Mercury command and control aircraft. Both planes are maintained at Tinker Air Force Base.

The engine renovation project will boost efficiency and increase reliability of the engine by replacing components, said Brian W. Johnson, Chief, F101/F108/F110/F118 Branch, Propulsion Sustainment Division, Air Force Life Cycle Management Center.

"We're installing newer parts," including new high-pressure turbines, compressor blades and vanes, during the rehabilitation project, Mr. Johnson said. Afterward, the engine will be "much more reliable and durable," he added.

The engine renovation project is referred to as C-PUP (for CFM Propulsion Upgrade Program).

After the overhaul, the engines will consume less fuel and money, Mr. Johnson said. The savings -- from fuel conservation and avoided maintenance expenses -- have been estimated at more than $2 billion for the Air Force and the Navy combined.

Testing indicates fuel efficiency will increase by 1.5 percent to 1.7 percent, said Tim Misner, the F108 engine lead program manager at Tinker. The fuel economy alone will be a substantial savings because, "This fleet gets a lot of use," Mr. Johnson noted.
In addition, the engine refinement will reduce maintenance costs significantly, Mr. Misner said.

The F108 engine has been a reliable producer for many years. More than half of them on KC-135s have not been reworked since they were bolted onto the aircraft's wings, some as far back as 1984, records reflect. (The Air Force's Air Mobility Command supervises 414 Stratotankers, including 247 that are assigned to the Reserve and the Air National Guard.)

F108 engines have "been in use for a long time, and a lot of them have not yet been back to the depot for maintenance," Mr. Misner said.

The upgrade is expected to add years of life to the engines. "With these improvements, we expect the engine to stay on wing for 20-plus years," said Steve Walsh, logistics management specialist in the F108 Program Management Office in Bldg. 3001.

A Business Case Analysis indicates the Air Force can anticipate savings of $6 for every $1 it spends on the C-PUP, according to Maj. Mark A. Blumke, Deputy Chief of the Maintenance Systems and Integration Branch in the Air Mobility Command headquarters at Scott AFB, Ill.

The majority of the F108 engine repair work will be performed organically at Tinker, Mr. Misner said.

The initial upgrades for the Air Force will start during the third quarter of fiscal year 2013, when several engines are brought to Tinker and torn down, and the jobs will be completed in the fourth quarter, Mr. Misner said. Seventy flow days are allotted for a C-PUP overhaul, he said.

The schedule calls for 60 engines from KC-135s to be upgraded next year, doubling to 120 engines annually in following years until all 1,440 F108 engines in the KC-135 fleet have been overhauled, Mr. Johnson said. The process is projected to take 12 years to complete.

Approximately nine F108 engines from Navy E-6Bs will be upgraded at Tinker AFB in early FY13, but whether additional engines from the Mercury will be upgraded here has not been determined, Mr. Misner said.

The genesis of C-PUP occurred about four years ago, when the Navy and the Air Force both were trying to restore lost engine efficiency. No more than half of the engine life could be regained after an overhaul, Air Force and Navy officials said.

CFM International, the engine manufacturer, "had a proven upgrade for this engine family in their commercial fleet," Mr. Johnson said.

Since the improvements were too expensive for the Navy to implement unilaterally, CFM International suggested a collaboration with the Air Force that would be mutually advantageous. Authorization to proceed with the design improvements was given in 2010, and the Navy and the Air Force combined efforts to share the costs of flight and ground testing.

The Defense Department has earmarked $159.5 million over the next five years for 493 of the F108 engine upgrade kits. That includes 93 kits in FY13 and 100 kits per year in FY14-FY17, Major Blumke said.

A key reason the Air Force needs this upgrade is to keep pace with additional demands on the KC-135 that are extending its life, Mr. Johnson said.