Bernie Baldwin reports on the maintenance and repair programmes supporting the record-breaking CFM56 engine family, and those being put in place for its successor, the LEAP engine range.

    The engine upgrades to the narrowbody aircraft of Airbus and Boeing have arguably created the biggest story in the airline industry during this decade, lengthening the lives of airframes which have been central to air transport.

    While the CFM56 from CFM International has begun to make way for LEAP engines on both the A320 and the 737, there is still a vast MRO market for the former powerplant.

    LEAP engine range

    “The CFM56 is expected to generate high volumes of MRO demand in the next five years, and in a buoyant CFM56 engine market, operators and MROs are struggling to induct engines because there are so many of this highly successful engine type in operation,” explains Aero Norway’s chief business officer, Rune Veenstra.

    “The -5 and -7 have performed particularly strongly on-wing, leading to delayed shop visits. Some engines listed for a first shop visit in 2015 and 2016 will only be going in for repair in 2018 and 2019. This led to an unexpected shortage of work in 2015-16.

    “However, since the beginning of this year right through to 2020, operators may struggle to get their engines into the shop. Aero Norway originally forecast a 60 per cent to 40 per cent split in 2018 between the -3 compared to the -5 and -7. However, demand has been so great for the latter pair that it is likely to be closer to a 30-70 split in favour of CFM56-5B and 7B,” Veenstra confirms.

    “Aero Norway predicts that peak demand for the CFM56 will occur from now through to 2021 at our Stavanger engine MRO facility, and we anticipate it will soon be running to full capacity of around 120 engine inductions. Investment strategies have been put in place to meet this pent-up demand,” he adds.

    A similar assessment comes from Florent Leforestier, vice president products & business development engine services, SR Technics. “The [CFM56s] are longer in use than expected, the demand for engine MRO services is increasing and this is unlikely to change before 2023,” he predicts.

    LEAP engine range

    “SR Technics has kicked-off a ramp-up plan already in December 2017, with the target of increasing its shop capacity by 50 per cent, from 200 to 300 shop visits a year, by the fourth quarter of 2019. We expect the CFM legacy engine shop visits to peak around 2024.”

    Peter Turner, president airlines & fleets at StandardAero reports that third party market data sources suggest that the CFM56-7B engine MRO market is in excess of $4 billion and growing.

    “We are looking to extend our CFM56-7B services to any airline customers of our legacy Vector Aerospace businesses that might also operate the 737NG,” he remarks. “In addition, we have begun work with the US Navy for engine services on their growing fleet of P-8 Poseidon aircraft. This was a natural progression after a long history of engine maintenance on the P-3 Orion.”

    ST Engineering Aerospace is another MRO company expecting continued high demand for maintenance work on CFM56. “There is still a large number of engines in operation that have yet to undergo their first heavy maintenance. These engines will also require a few shop visits over the next few years,” observes Choo Han Khoon, the company’s EVP of engine total support. “As for the LEAP engine, that only entered into service in 2016, and is expected to stay longer on-wing. It is projected to be due for heavy maintenance in 2023 at the earliest.”

    Operators of the CFM products are continually on the lookout for support packages which benefit them both in terms of price, reliability and turnaround time (TAT).

    “ST Engineering solutions cover not just heavy maintenance, but also services ranging from line maintenance, on-wing support maintenance and fleet management,” Choo states. “In addition, we have aircraft/engine leasing services and are able to provide MRO services through an integrated package if that’s what our customers want.”

    In creating its support programmes, StandardAero starts by working with the customer to understand the latter’s concerns and goals for each individual repair, whether their focus is on cost, performance, build life or otherwise, according to Turner. “Our engineers then develop workscopes that will provide maximum efficiency and longevity of the engine in the most economical way possible,” he declares.

    “It is almost always more economical for the end customer, and more profitable for the MRO provider, to repair a part rather than replace it. In cases where a part repair might be a prohibitively long process, we may use rotable pools of parts to expedite return of the engines. However, some operators are very particular about getting their original parts back. It’s all about balancing the customer’s expectations on turnaround time, price, and pedigree of the parts installed in their engine,” Turner comments.

    Like StandardAero, Aero Norway is an authorised independent CFM56 repair facility and also takes a collaborative approach which Veenstra says appeals to operators and lessors alike. “We concentrate on sustaining flexibility of workscope for all customers,” he emphasises.

    “To best serve our customers – MROs, independent engine owners and leasing companies – we have taken steps to underpin the business in three fundamental ways: financial support to deliver working capital; sourcing of repair partners that can complement the flexibility of workscope that we, as an independent organisation, strives to offer; and the development of highly-trained apprentices to ensure continuity of the company’s engineering skillsets for the next 20 years and more.”

    Incorporated into those packages, of course, are the repairs and modifications that are required on a shop visit. Despite its longevity in service, new repair techniques and processes for the CFM56 continue to be added.

    Johannes Wallat, head of process engineering & laboratory, engine services at SR Technics, notes that the company has developed and implemented 10 new source approval repairs on the CFM56-5B/-7B combustion chamber on the inner and outer liner.

    “These 10 repairs required intensive process development such as drilling cooling hole patches with a laser into the combustion chamber, the reapplication of the plasma coating, and the realisation of the defined airflow demands for sophisticated processing,” reports Wallat. “In addition, SR Technics developed the airflow test stand itself, which is of course OEM approved. The development of complex equipment and tooling has a significant impact on the cost structure.

    “On the component side, for example when it comes to nacelle and thrust reversers for the CFM56, SR Technics developed multiple repair solutions for structural metallic and composite parts, acoustic panels and skins,” Wallat continues,

    “and it can be said that on these components, the lead times for spare parts and/or OEM repair solutions play a major role on component availability and maintenance cost. Therefore, it is a clear advantage to be able to provide one’s own repair designs to reduce costs and TAT.”

    SR Technics can do this because it holds EASA Part 21J design approval. “Thanks to the bilateral agreement [with the US] these repair designs are also FAA approved. Also, EASA Part 21G production organisation approval enables us to manufacture specific spare parts in our own facilities, or use external sources to provide flexible and fast solutions,” Wallat avers.

    At ST Engineering Aerospace, a new Smart Robotic Grinding System was developed this year for fan case abradable removal and repair. “This automates the grinding process of the fan case abradable during removal and finishing,” Choo explains.

    “Whereas a turnaround time of almost a week was necessary prior to the introduction of the robotic system, this new solution has managed to reduce the time needed for the process to under 10 hours.” And when time is money for an airline, that’s a considerable bonus.

    Aero Norway has been working in a similar area. “We have just invested in a new state-of-the-art high speed grinder that will be operative in third quarter 2019,” Veenstra confirms. “We are constantly evaluating and implementing new repair capabilities that will benefit our customers.”

    StandardAero’s Turner focuses attention on the CFM56-7B for the 737NG family. “This is subject to the same kind of regular maintenance as many other engines: oil servicing, borescope and visual inspections. As the engine ages, additional field-level inspections come up on the fan blades and turbine rear frame. As a credit to the reliability of the CFM56-7B, a large majority of engine removals are driven by the expiration of life-limited parts (LLPs). Indeed, customer convenience is sometimes a reason for removal than most of the other engine condition issues,” he reports.

    “At present StandardAero is not licensed to perform work on LEAP engines. However, we expect to maintain our strategic OEM partnerships into the future, including the LEAP and other newer engine platforms,” Turner adds. “A number of our existing customers are adding the LEAP engines to their fleets, and we want to continue to service those customers.”

    SR Technics is on the same road. “When it comes to the maintenance of next generation engines, such as the LEAP, and you have obtained the respective licences, tools and equipment, SR Technics will adapt to the market with an adequate implementation of the required procedures on the technology side,” Leforestier declares.

    “You need the respective competence, and here experience truly adds value, as the repairs will become more complex. Hence, you need to introduce new developments and innovations,” he stresses. “In SR Technics Airfoil Services for example, where we have capabilities for turbine blades and vanes, we have been following new developments and innovations such as micro laser cladding, automated inspection and digital recording of defects to cope with these new materials.

    Working on a LEAP engine

    “In addition, the exchange and management of the data, for example, with regard to enhanced condition monitoring of engine parameters, will be a challenge, as  the role between owners and operators are not clearly defined in that sector. This is very important for the predictability of maintenance events,” Leforestier contends.

    While the MRO companies work on their LEAP support ideas, CFM itself has been working on its programmes and packages to provide benefits it believes a customer airline can only get from working with the OEM. “The first way CFM differentiates itself is structurally,” remarks Jamie Jewell, director, strategic communications, CFM International.

    “From an MRO perspective, our approach is unique: the CFM support model is open and competitive. The higher degree of competition creates a channel for used serviceable parts. MROs and airlines seek out these used parts to reduce maintenance cost, and the bidding market for the parts drives a high salvage value for engines. Airlines, lessors and investors all benefit.

    “Another aspect of CFM differentiation is that our model results in greater airline choice of service structures, as MROs compete to best meet the airline customers’ needs,” Jewell continues. “For example, an airline might select a risk transfer contract early in an engine’s lifecycle, and may migrate to other time and material products later in the lifecycle, when the industry understands maintenance cost risk.

    “CFM also differentiates its service through customising workscopes to specific customer objectives. This is especially popular in the mature phase of a programme when customers may need an engine overhauled, but have a limited operating horizon and desire to minimise maintenance investment,” she adds.

    As for new repair techniques and processes, Jewell says that between the -5B and the -7B, there have been about 60 repairs developed in 2018, the majority of which help improve cost of ownership.

    With production gradually switching from a majority of CFM56s per year to more LEAP engines built each year, Jewell confirms that there are many improvements which airline maintenance departments and independent MRO suppliers will notice as a result of LEAP family engines having been designed for better maintainability.

    LEAP engine range

    “We spent a lot time in the early design phase of the LEAP engine talking with customers to understand their priorities. Obviously, ease of maintenance was one of them,” Jewell comments.

    “As we got to the final stages of the engine design, we put together a maintainability team to assess the design from the maintenance perspective. The team developed a 3D model of the engine that was used to check access to every part in a virtual reality environment. We used the same virtual environment to determine the placement of line-replaceable units (LRUs) and features to enable easy access, removal and replacement. We targeted a ‘remove/replace’ time of 30 minutes for most of the LRUs, sensors and other replaceable parts,” Jewell elaborates.

    “Perhaps the biggest maintenance design decision was to put the accessory gearbox and major LRUs – electronic engine control, hydraulic and fuel-pump systems – on the fan case. That allows immediate access to these units when the plane lands so that any issues can be quickly addressed.”

    As with many major new programmes, there have been some teething issues with the LEAP engines. Jewell goes through some of these and explains how each was solved.

    First up is the LEAP-1A Starter Air Valve, an external part. “For a while, this was the leading cause of delays, but a new part was developed and introduced last year which has reduced delays and cancellations – and further improvements are planned,” she notes.

    “The LEAP-1B low pressure turbine (LPT) disk experienced a ‘manufacturing quality escape’. Although 30 disks have been removed, these were all caught in production, so none entered service and there were no AOGs and no findings. Similarly, the LEAP-1A high pressure turbine (HPT) Stage 2 Disk suffered a ‘manufacturing quality escape’. Here, 74 disks were involved and all were removed with no AOGs and no findings.

    Boeing 737 MAX 7 First Flight Air To Air

    “Next, CFM observed premature loss of the environmental barrier coating (EBC) on the HPT shroud of the LEAP-1A and LEAP-1B engines. This coating loss manifests itself in a shift in exhaust gas temperature margin (EGTM),” Jewell continues. “LEAP engines are delivered with substantial EGT margin and a loss of that margin has no immediate impact on flight operations. As the margin is consumed, however, the engine will need to be removed and restored.

    “To deal with this, a software upgrade was introduced that gives up to 40°C additional EGT and an improved shroud with thinner coating is now the production configuration as well as being available for retrofit,” she adds. Inclusion at the line-fit stage began with June 2018 aircraft deliveries.

    In conclusion, Jewell emphasises the LEAP engine design is actually very stable. “This has enabled CFM to keep operational disruptions to a minimum as we continue the very steep production ramp up. The majority of the issues have been with external hardware,” she notes, adding emphatically, “No major component has required a redesign.”