MR-Engine-MTUMaintenance_promo.jpg MTU Maintenance

Engine Repair In The Digital Age

Maintenance partnerships and predictive maintenance are changing the landscape for engine repairs.

Printed headline: Engine Repairs Evolving

With the increasing numbers of new engines sold including OEM support agreements, independent engine maintenance providers tend to focus on repairs for current-generation technology. The manufacturers, meanwhile, are developing new techniques and extending established repair processes to new platforms in order to maximize the value of their flight-hour-based contracts.

The cost of new parts means that even for the OEMs it makes sense to develop repairs for engines under flight-hour support deals, while independent MRO providers are best served by investing in repairs for high-value parts on the most popular engines. On the other hand, there is little impetus to develop repairs for older engines with limited remaining lives, where performance and life-cycle restoration is uneconomic for users.

Operators of mature engines are more likely to choose alternatives to repair, such as replacement with used serviceable material (USM) or even green-time leasing. That said, the rapid growth of the USM market also means growing demand for repairs, as parts providers seek to refurbish and remarket the most valuable life-limited parts (LLP).

There is also a trend toward more on-wing and near-wing engine inspections and repairs, which has seen the creation of more mobile repair teams. MTU Maintenance has on-wing and near-wing services that encompass top-case repairs, fan-disc changes, high-pressure turbine (HPT) blade replacements and low-pressure turbine (LPT) nozzle replacements on different engine types up to and including LPT Level 6 blade replacement on a GE90.

Mixed Market

Differentiating engine repair types between OEMs and independent MROs is useful to illustrate certain market fundamentals, but the reality on the ground is more complex. For example, an OEM might be responsible for an engine’s support but delegate much of the actual maintenance to authorized service providers and alliances.

Numerous such partnership deals have been signed in recent years, with more likely to follow. Rolls-Royce has joint ventures in Singapore and Hong Kong—SAESL and HAESL—but is seeking more capacity, both to perform and develop repairs on its newest engines.

“We definitely need capacity but also need the right capabilities,” Scott Holland, Rolls-Royce’s vice president for marketing, Europe, told Aviation Week earlier this year. “The challenge is that there are few companies that do it and do it well,” he added.

Rolls-Royce has reached out to independents such as StandardAero and Delta TechOps, while other OEMs have also pursued partnerships. Examples include a recent deal between CFM and MTU Maintenance Zuhai to support the Leap; XEOS, the joint venture between Lufthansa Technik and GE Aviation in Poland for GEnx engines; Airfoil Advanced Solutions, a Safran and AFI KLM E&M venture to repair high-pressure compressor blades and variable stator vanes; and SIA Engineering’s joint ventures with all three major engine OEMs.

Despite these burgeoning alliances, it is uncertain whether larger maintenance and repair networks will provide sufficient capacity to completely avoid the bottlenecks that have occurred recently when large numbers of overhauls fall due. This could mean more access to repairs of newer engines as OEMs are forced to bring more independent providers within their service networks. Whether this situation will lead to MRO providers developing more repairs themselves is difficult to forecast, since independent MROs will have to balance their commitments to the OEMs, to their direct customers and to the mix of services they offer to ensure optimal profitability. What does seem likely is that independents will retain some autonomy regarding engine workscopes due to the limits of OEM oversight.

“The hurdles for the development of repairs are of a commercial nature. Is there a market and customer need for the repair? And is there a business case that carries the development costs?” says Friedhelm Kappei, head of industrial engineering for MTU Maintenance. He adds that the best repair candidates tend to be high-value parts such as the HPT, high-pressure compressor (HPC), LPT and combustors

New Techniques

OEM and designated engineering representative repairs offer an alternative to expensive replacement with new parts, although capabilities vary across shops. MTU, for example, offers many repairs across a range of engine types, with Kappei noting that its most advanced techniques are often favored by operators who own engines over the entirety of their life cycles.

MTU is exploring techniques such as single-crystal welding, automated blending and artificial-intelligence-based automated inspection to improve its repair processes. Joint-venture engine manufacturer CFM is also a fan of automated inspection, noting its advantages for productivity and repeatability.

GE AviationMR-ENGINE-2_GE-Aviation.jpg

Cold spray repair is used at Apulia Repair Development Center run by Avio Aero, a GE Aviation unit in Italy.

Lufthansa Technik, meanwhile, has been at the forefront of automated engine repair with its AutoInspect and AutoRepair robots. AutoInspect performs digital crack inspections on engine components with the help of high-end sensors, a task previously done by hand with dye penetrants, while AutoRepair is intended to complete the automation chain by repairing combustor components after they have been robotically inspected.

Other inspection methods also provide gains on the repair side, observes CFM. “Laser-based inspections have been used to improve corrosion identification, helping to reduce scrap and workscope,” says Rhonda Sample, director of GE Aviation Repairs. “Improved on-wing inspection techniques allow better resolution than traditional borescopes, preventing early engine removals.”

GE is also exploring new repair techniques such as cold metal transfer (CMT) and cold spray. Originally developed for the GE90, CMT uses a robot to perform low-heat additive repair for seals on rotating parts, cutting repair cycle times by more than half. Also pioneered on the GE90 is cold spray repair, in which solid powder particles are fired at four times the speed of sound through a nozzle attached to a robotic arm. When the particles hit a substrate layer, they behave as a liquid, rapidly cooling and forming an atomic fusion bond. GE has refined the process by adding a second robot arm to manipulate the object being sprayed and by using artificial intelligence to analyze the results.

A form of additive manufacturing (AM) already in general use for engine repairs is laser metal deposition (LMD). Also known as laser cladding, this process uses a laser to generate a weld pool on the component surface. Material is then added to the melt pool as a powder or wire, and the melted particles fuse and solidify while the nozzle is manipulated to add the desired structure to the component.

Lufthansa Technik offers laser cladding but also is pursuing powder-bed-based AM repairs, in which powder must be applied to an existing component, rather than being fused or melted inside a standard AM platform. As a result, specific fixtures must be developed for each component to be repaired. Despite such difficulties, Lufthansa Technik expects to have its first powder-bed repair certified for 2020.

Clearly, AM-based repairs promise big gains for the repair business, yet AM will also bring its own challenges as OEMs apply the process to actual production of increasing numbers of engine components. AM-based and other repair techniques may not be suitable for all of the new engine parts, necessitating another round of innovation within OEM and MRO repair departments.

At CFM, Sample says AM “opens up flexibility to think differently about repair techniques.” She adds: “In general, the value proposition for additive for new part production opens the design space to make a part with higher performance and can, to some extent, simplify the supply chain.”

Data In, Data Out

Predictive maintenance based on data analytics and engine-trend monitoring is designed to extend time on wing and identify the optimal point to remove engines. This reduces demand for repairs and materials, saving operators money, but can also improve the repair process by allowing engineers to assess the effectiveness of previous repairs.

However, there are also concerns that predictive maintenance could complicate the repair process for certain parts in engines and aircraft when they are removed preemptively without a fault code.

“Troubleshooting a component off-wing is harder because of all the missing system sensors, logic and monitoring circuits that are captured in the fault codes,” notes Ahmed Safa, divisional senior vice president for engineering at Emirates.

“An MRO that gave a fixed-rate repair contract to the airline will be running against the clock where you must diagnose, correctly repair and return a part to the airline within contractual turnaround times,” Safa says. “This situation could result in parts being returned to serviceable inventory without a good repair, leading to an increase in rogue units or a large uptick in inventory float levels due to longer turnaround times and higher removal rates.”

Another open question concerns the reliability and repairability of the newest generation of engines. Following the unprecedented times on wing recorded by current-generation CFM56 and V2500 engines, many expect their successors—the Leap and PW1000—to perform as well or better, with fewer but heavier shop visits predicted. This might alter the repair cycle, although numerous problems across the Rolls-Royce Trent 1000 family have shown that newer is not always better.

“As with any new technology, one needs to see how [new-generation engines] perform on wing and in various operating environments,” says Kappei. 

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