Production of CFM International engines may be shifting to the new Leap generation, but maintenance of the latest CFM56 variants will be a growing activity for years to come.

In 2016, output of CFM56-5Bs and -7Bs reached its highest level in the engine family's history at 1,665 engines as Airbus and Boeing ramped up their respective A320-family and 737 production rates.

About half of in-service A320ceos are powered by CFM56-5Bs, and the rest by International Aero Engines V2500s. The CFM56-7B, meanwhile, is the sole powerplant available for 737NGs.

CFM says just over 22,000 CFM56-5B/7B engines have been delivered. Around 70% of these have not yet been taken off wing for their first overhaul shop visit, the GE-Safran joint venture adds. "We expect CFM56 overhaul demand to remain strong for the next decade and beyond," it notes.

Shop visits are driven by a need to either restore engine performance or replace life-limited parts at the end of their lifecycle. The frequency of shop visits depends on the aircraft's operating conditions. Environments with high atmospheric sand or dust levels pose a particular challenge, as particles can damage aerofoils in the compressor – with an associated loss in efficiency – and block cooling holes in hot-section components, which accelerates part degradation. In hot areas, pilots may require increased power during take-off as engines operate less efficiently than in cold air, which also leads to increased wear and tear.

Highly stressed parts in the high-pressure turbine are typically replaced first, followed by parts in the HP compressor, says Frank Bodenhage, general manager of MTU's overhaul joint venture with China Southern Airlines' parent in Zhuhai. But he adds: "We see on CFM56s LLPs [limited-life parts] with generally high cycles and high flight-hours… which often reach their design [life] limits."


Until now, there has been a clear distinction between overhaul activities for CFM56-5B/7Bs and for the previous CFM56-3 generation, which powers 737 Classics, says Bodenhage. While the modern engines tend to be serviced with the aim of maximising time until the next shop visit, MRO providers typically employ used serviceable material, repair parts and tailor workscopes on older engines in order to reduce maintenance costs as the legacy equipment approaches the end of its lifecycle. If the equipment is too old to undergo extensive repair work, operators might forgo a shop visit altogether and buy or lease used replacement powerplants that have enough "green time" – service life – left.

Bodenhage says these customised activities start to apply for the latest CFM56 engine generation too. "We're beginning to see [some] -5B/7B engines are maturing, and we are entering an area where more and more of these engines – also because the successor generation [Leap] is coming on the market – need to be maintained at lower cost," he says.

Lufthansa Technik says CFM56 engines offer "excellent opportunities for cost optimisation" as a wide range of part repairs, material-sourcing options and maintenance approaches have been developed for the powerplant family. The MRO provider's senior-vice president of engine services, Bernhard Kruger-Sprengel, notes that "every [CFM56] engine type has its specialities".

As thrust capability has been maximised on the engine family's sole long-haul derivative – the CFM56-5C, which powers first-generation A340s – Kruger-Sprengel says that version "comes with some challenges relating to EGT [exhaust gas temperature] margin". However, he points out: "We have developed customised MRO concepts and made significant progress in addressing the specific problems."

As airlines have retired A340s and CFM56-5Cs have become available – either as spare engines or parts sources – Lufthansa Technik has been able to reduce MRO costs by installing used serviceable material or swapping engines and thus avoiding shop visits. "Our customer airlines can operate the A340-300 at even lower MRO costs than for a comparable twin-engined aircraft," Kruger-Sprengel says.

In 2015, Swiss maintenance specialist SR Technics formed a partnership with UK asset manager AerFin in order to gain access to CFM56-5C engines and used material. Earlier this year, the two sides expanded their joint venture to include services for CFM56-5B and -7B engines.

A key factor in determining an MRO regime for engines is the ownership situation – does the equipment belong to the operator or a leasing company? Lessors typically require that only OEM parts and OEM-approved repairs are used to service the engines, in order to maintain their market value. Citing the work of third-party appraisers, CFM says engines that fulfil these criteria have "up to 50% higher residual value" than other powerplants.


Much effort has gone into developing processes to repair rather than replace damaged parts in a bid to reduce MRO costs. CFM notes that it devises, on average, about 50 new part repairs a year for the engine family. The manufacturer acknowledges that repairs are especially important for sophisticated new components, such as blisks, where damage on individual blades should not lead to the entire part's replacement. CFM says its repair development is concentrated on reducing scrap rates on high-value components.

However, there is concern that existing repairs cover only a select range of parts and failure modes. Air France Industries KLM Engineering & Maintenance notes that repairing 3D aerofoils, for example, can be a "quite challenging". While repairs were developed for HP compressor blades on earlier CFM56 models, the MRO group says "not all the existing repairs" have been extended to the -5B/7B series.

"There is a trend of an increasing number of repairs requiring a licence agreement with the OEM," says SR Technics' head of engine services, Roberto Furlan. The Zurich-based maintenance specialist tends to develop new repairs in co-operation with the OEM. But Furlan expects such developments to become more difficult on new-generation engines. "Keeping a high level of in-house repair capabilities will become much more challenging for independent MRO providers," he says. "The complexity of parts might even change the current repair-versus-replace business set-up for certain parts."

Today's CFM56 family is covered by "probably the most comprehensive range of repairs available [compared with other current engine series]", in the view of Kruger-Sprengel. He adds: "Every year new repairs evolve." Lufthansa Technik is independently developing repairs – like other maintenance specialists, including MTU – under a designated engineering representative approval. These DER repairs tend to be used for operator-owned engines only, and such developments are only feasible for financially strong MRO providers with access to fleets where the repairs can be applied.

CFM says competition with third-party maintenance and material providers is central to its open MRO network strategy as it encourages maintenance cost reductions, and that this approach will be continued in "similar" manner for the Leap generation. Lufthansa Technik was revealed last year as an external overhaul partner for the new engines. AFI KLM E&M says it wants to extend its CFM56 activities to become a "major player" in Leap MRO. And MTU confirms an interest in servicing the new engine, although no formal decision to introduce it has yet been made.

The number of third-party overhaul providers is likely to grow after 2020 when shop visit demand is set to rise, CFM suggests. The Leap engine entered service in 2016, and requirements for unscheduled events during the initial period are typically covered by OEM warranties.

Maintenance providers acknowledge that it will be a challenge to service new Leap technology such as ceramic matrix composites and carbonfibre fan blades and cases. However, the CFM56 maintenance business over the past few years has shown that technical capabilities alone might not suffice any more for an MRO to be a significant player in the field. MRO specialists must also be able to provide access to used serviceable material, repair options, used engines – for lease, sale or teardown – and on-wing maintenance teams. While the number of scheduled shop visits on new-generation engines is set to decline versus older products, AFI KLM E&M says "we expect more minor interim repairs between two overhauls". Furthermore, engine trend monitoring and predictive maintenance have assumed an important role in maximising an engine's time-on-wing.

These additional activities would seem to favour the OEM and large maintenance providers, as smaller overhaul shops are less likely in a position to make the required investments. But the demand for broader aftermarket services might present an opportunity for smaller overhaul shops to form partnerships with other specialists. After all, the in-service fleet and maintenance market are growing.

Source: Cirium Dashboard