04 July 2024
New Engine Technology - The Challenges Continue
In this feature article, David Hitchen, Regional Director, Middle East and Africa at McLarens Aviation shares his insight into the challenges surrounding new engine technology and how the lessons learned can benefit the risk management of future new engine projects.
When I was asked to write a piece on this subject a year or so ago, I discussed the technological developments behind the latest offerings from the main engine manufacturers. I touched on the issues being encountered due to that technology being pushed to what many feel is close to the limit for conventional turbo-fan engines. At the time, I surmised that the New Engine Options (NEOs) on the latest versions of the B737 and A320 would continue to experience a high number of premature removals, however, the peak would soon be reached, and the situation would steadily improve as more shop capacity came online during 2023 and 2024. A week is a long time in politics, as the saying goes, and it would seem equally true when predicting the fortunes of new engine types as their launch into the market continues. Shortly after the piece was published, a new issue arose with one of the types resulting in additional short-notice engine removal requirements and a further increase in the number of aircraft out of service. This was not, however, related to the durability of the new technology, it was in fact, the result of a tried and tested manufacturing technique experiencing a quality assurance shortfall. This type of issue has become topical in the industry, given the difficulties Boeing are experiencing on the B787 and B737MAX production lines, and with one of their main Original Equipment Manufacturers (OEMs).
David Hitchen
Regional Director, Middle East & Africa
McLarens Aviation
The quality imperative
Quality is an essential aspect of most industries and is especially important in aerospace. It has been a cornerstone of the continuous improvements in aviation safety over many years and goes hand in hand with technological advances. Where rare escapes have occurred in manufacture the effects are often felt much later, sometimes years, therefore the need to identify the exposure and restore the integrity of the production systems can arise long after the initial occurrence, at a point where many affected parts are already in service. A unique quality lapse in a maintenance environment, where it can be contained and quickly resolved, is preferable to an obscure and difficult-to-identify failure in manufacture. The effects can be widespread, none more so than in new engine-type production where the advanced technology needs to be anchored to tried and tested production techniques where possible. The issue in this case affected the Pratt and Whitney PW1100 engine and its timing impacted the ongoing modification programme which was addressing the various durability issues. Unwelcome as it was, unlike the durability problems, the issue in this case was more one of management. The risk mitigation was clear, and the solution was already in place, it was simply the timeline that unfortunately had to be pulled forward.
"Quality is an essential part of most industries and is especially important in Aerospace"
Powdered metal contamination
The problem first came to light with the International Aero Engines (IAE) V2500 engine following an investigation into an uncontained High Pressure Turbine (HPT) failure in March 2020. The same Original Equipment Manufacturer (OEM) is involved in the production of HPT discs for both the V2500 and the PW1100. The manufacturing process for these parts involves a powdered superalloy pressing technique which achieves a much higher strength in the finished part than casting and machining. This complex process has been employed successfully for decades with the first engine using the technique being produced in the late 1970s. A critical element of the manufacturing process is ensuring that undesired particles cannot be introduced to the powder as the inclusion of even a microscopic contaminant may have a detrimental effect on the fatigue strength of the finished part. This was identified as the cause of the 2020 V2500 failure and it was established that discs manufactured since 2015 may be affected by the same issue. The source of the problem was eliminated at that point; therefore, it was the parts manufactured between 2015 and 2021 that were at risk.
Airworthiness Directives (ADs) were issued by the regulators, and multiple V2500 engines were removed from service for shop inspection of affected HPT discs. Whilst this was challenging for operators, shops and the OEM to deal with, the issue was broadly managed due to the maturity of the engine and the life variation of those affected. It still resulted in multiple unscheduled engine removals and aircraft being out of service due to insufficient spare engines being available.
Following a wider examination of the quality escape, it was established that the same issue potentially affected parts installed in the PW1100 engine fitted to the A320NEO family. The analysis at the time, indicated that a regime could be adopted which would enable safe management of the problem. Despite fatigue calculations reducing the life of the parts, the vast majority were expected to undergo the required inspections during scheduled shop visits. Unfortunately for all concerned, the situation changed in 2023 following the investigation of a PW1100 In Flight Shut Down (IFSD). The findings led to the fatigue assumptions being revisited by Pratt & Whitney and it was established that they were overly optimistic. A new regime was developed, and the fleet plan was revised with reduced life limits. This had a significant impact on operators, many of whom were still dealing with the durability issues that had already led to multiple engine removals and aircraft being taken out of service.
The AD issued by the regulators in response to the escalated significance of this known issue resulted in almost 200 engines requiring removal in a matter of weeks from the AD being issued, and up to 1,000 engines being affected over the following 12 months. Beyond the obvious operational disruption and business impact on the airlines, the OEM who manufactured the parts had to make a USD3 billion write-down to account for their cost exposure.
It is worth bearing in mind that this was not the result of new technology failing to be as durable as anticipated. This was a latent quality lapse in a technique successfully used in manufacturing thousands of different metallic parts for a wide range of applications from aerospace to nuclear energy. In any manufacturing quality escape, it is always concerning when the postproduction inspection does not identify the issue, as was the case in this instance. If it had been identified in the factory, a solution would have been found quickly to eliminate the source of possible contamination and no affected parts would enter service. With the parts successfully passing post-production inspection, hundreds were installed in new engines causing significant exposure, ultimately resulting in up to 25% of the worldwide PW1100 A320NEO fleet being out of service due to a lack of engines.
No doubt lessons have been learned, and both the OEMs and regulators involved reacted quickly to the findings of the two investigations to ensure appropriate control measures were put in place, and ensure safety was not compromised. Of course, it is better to suffer business and operational disruption than a safety issue with the potential for not only IFSDs but, more significantly, uncontained failures.
Harsh environments and non-synchronous vibration
Whilst Pratt & Whitney and their customers have been grappling with the PW1100 issues, CFM has suffered lesser but still operationally disruptive, problems with the LEAP 1A and B engines, particularly in their harsh environment durability. Airlines in the Middle East region, in particular, are experiencing premature engine removals as a result of accelerated HPT wear caused by the harsh environment. In some cases, due to an ongoing lack of spare engines, aircraft are again being taken out of service. Most of these issues are caught before failure through an enhanced borescope regime, however, there have been IFSD events resulting from HPT failures. Re-designed hardware is available and is being incorporated during the shop visits. Time will tell whether this will solve the problem, noting that it is only in-service experience in such environments that really test the durability of the HPT.
There have been two further recent ADs, issued against the LEAP 1A engine, one relating to the interstage seal in the HPT of certain engines which may have sub-surface anomalies that occurred in the manufacturing process. These inclusions, similar to those on the PW1100, could result in premature fatigue of the part and possible failure. Measures have therefore been applied to remove the parts from service. Thankfully for operators, the number of affected engines is small in this case. Again, it is a manufacturing technique issue, not one related to the design of the part in question.
Another AD was recently issued in respect of Non-Synchronous Vibration (NSV) that could affect the life of some critical parts of the engine. The issue is due to the part of certain No.3 bearing installations that has the propensity to wear prematurely and cause NSV which could lead to excessive seal rub between the HPT rotor and stator. Whilst this is not critical, it could result in conditions in the secondary air system that may ultimately lead to an HPT disc failure, hence the AD.
The short-term need to deal with several key issues on both engine types will continue to impact airlines through 2024 into 2025. The hope is that the extent of the issues is at least now understood, and solutions already identified and implemented. The challenge is working through the practical fixes as quickly as possible to return the global fleet to full operational status.
The short-term need to deal with several key issues on both engine types will continue to impact airlines through 2024 into 2025.
Enhanced shop capacity
The key to reducing the backlog of engines awaiting repair is increasing the shop capacity and reducing the Turn Around Time (TAT). This has required a huge investment on the part of both main manufacturers, including partnerships with independent shops, to supplement the OEM’s own network and capabilities. Pratt & Whitney has entered into such agreements with SR Technics, Lufthansa Technik, EME Aero in Poland and OGMA in Portugal as well as partner OEM shops, such as MTU in Germany and China and Pratt & Whitney in the US. The engines are subject to the manufacturer's sale and maintenance agreement therefore the OEM is the customer for the various independent shops and the airline’s commercial relationship is solely with the OEM. This is typically how new engines are purchased and maintained by the airlines, gone are the days of time and material shop visits, huge Powerplant Department budgets, and accumulating maintenance reserves held by lessors. All the main manufacturers sell their engine options based on life cycle maintenance and the business model is less related to the sale price of the engine than the ongoing income and profit generated by the shop visit requirements, the costs of which are charged on a cycle and hours-based criteria, broadly based on utilisation and operating environment.
Concerning the LEAP engine, CFM have enhanced their network with the inclusion of independent shops such as Air France-KLM, Delta Tech Ops, Lufthansa Technik, Standard Aero, and ST Engineering on full branded agreements with other shops such as MTU, SR Technics, TAP Maintenance and Engineering, SANAD and Sichuan Services Aero-engine Maintenance Co. being licensed service providers.
Bringing all of these shops up to full capacity in a short timeframe is the challenge both OEMs have been facing. In addition to producing modified parts, in the required volume to rectify the various issues, and return engines to the airlines with the benefit of them being resolved, rather than installing pre-modification parts which require the engine to return to the shop within a shortened life for the modifications to be embodied, assuming that is acceptable to the regulators.
Shortening the TAT is also essential to reducing the number of aircraft out of service. Some of the larger PW1100 operators have stated that their assumptions have been based on a 300-day TAT whereas, the target recently suggested by MTU is to perform a shop visit in 100 days if everything is in place, i.e. materials, shop capacity, vendor services etc. The not-insignificant challenge is to manage all aspects in harmony to achieve a substantial reduction of the 300-day average. In the short term, this is simply an effort to reduce the backlog of engines waiting at the shop door. In the longer term, if a reliable reduction can be achieved and sustained, it will make the whole process more efficient and reduce the number of spare engines that need to be provisioned with each operator. A rare benefit of the difficulties the manufacturers have been facing recently is that the creative thinking required to resolve the problems may have a positive long-term effect on the efficiency of shop production.
Protecting the production line
Once the dust has eventually settled, there will be a wealth of experience to draw upon and the hope will be that this will benefit the risk management of future new engine projects.
A critical aspect of the difficulties, faced by the OEMs, in solving the in-service issues is managing both sides of their business – sales and after-sales. To meet their commitments to the airframe manufacturers the OEMs must hit their production targets. This creates opposing needs between the requirement to return removed engines to the operators with modified parts installed and for newly manufactured engines to be of the latest modification standard. This inevitably creates tension, with the priority being the new production engines as the regulators and the customers require the engines to be of the latest available modification standard. This requires an insertion point to be agreed on the production line to ensure that the aircraft entering service after that point have the latest standard engines installed.
Unfortunately for Pratt and Whitney, the powdered metal contamination issue exacerbated this tension as a far greater number of engines were having to undergo shop visits due to a quality, not design issue. The compliance criteria of most ADs required that the modifications need to be applied at the next shop visit. This meant engines that were being successfully managed in service, pending modification shop visits, found themselves unexpectedly in the shop for the HPT inspections where they would have to stay until the required modifications could be embodied. These were competing for shop space and the parts were prioritised for new engine production.
CFM is experiencing a similar but much lesser issue on the LEAP 1A engine. The restrictions on the B737MAX production line mean that the LEAP 1B engine is proving easier to manage as the production rate is being held below that which Boeing had set as a target for CFM.
Overall, when comparing the situation now to that of last year, it seems we are in much the same place with the PW1100 engine. The anticipation was that by this point, the number of aircraft out of service would have reduced significantly as the shop throughput gathered pace. The impact of the additional removals required to address the powdered metal AD has been significant and set back the original target by perhaps 18 months. No doubt the increased shop capacity will accelerate the return to service of the affected engines, and the next 12 months should see a marked improvement in the situation. Once the dust has eventually settled, there will be a wealth of experience to draw upon and the hope will be that this will benefit the risk management of future new engine projects.
The LEAP engine has fared considerably better in terms of aircraft serviceability and the management of their in-service problems. The hope will be that the harsh environment durability improves as many of the operators with this engine type are based in the Middle East, and some of the notable recent orders for the LEAP 1A engine are from other airlines based in the region.
In Summary
- Engine manufacturers are under increasing industry pressure to provide new engine options with improved thrust, lower fuel consumption and greater service life to improve economic performance.
- To support growth, airlines and airframe manufacturers are demanding faster entry to service and higher delivery rates.
- As is always the case when pushing the boundaries of technology, the path to clearing a new engine type for operation on an aircraft is challenging.
- Setbacks and teething problems are anticipated, and manufacturers typically identify the root causes of such issues and develop solutions quickly, via multiple upgrades and modifications.
- In recent cases, such as with the PW1000, these issues haven’t been about the durability of new technology, but rather the result of tried and tested manufacturing techniques experiencing a quality assurance shortfall.
- This had a significant impact on operators, many of whom were still dealing with initial setbacks, that has led to multiple engine removals and aircraft being taken out of service.
- The hope is that the extent of the issues is at least now understood, and solutions already identified and implemented.
- The challenge is working through such practical fixes as quickly as possible, to return the global fleet to full operational status.
- Taking the history of engine development into consideration, it is evident that there are risks involved in achieving ever more efficient/advanced offerings.
- In the case of New Engine Options (NEOs), once the dust has eventually settled there will be a wealth of experience to draw upon and the hope will be that this will benefit the risk management of future new engine projects.
Let's talk
David Hitchen
Regional Director, Middle East & Africa
McLarens Aviation
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