Yearly aircraft maintenance spending fluctuates according to a number of factors—fleet age and size, intensity of modifications and airline profitability—that affect discretionary maintenance and upgrades. Historically, the most meaningful measures of MRO cost—real spending per flight hour or seat-mile—have been gradually trending downward.
This is true even though current-dollar maintenance costs, unadjusted for general inflation, may rise and despite the fact that inputs to maintenance, such as labor and parts, may escalate in cost. For example, U.S. mechanics’ wages increased 7-12% from 1999 to 2016 after adjustment for general inflation, and real engine-part prices were up 17% during the same period. But real MRO cost per flight-hour dropped 9% and real seat-mile expenses declined 17% as average seating capacity of aircraft grew.
These decreases are only 0.5-1% annually and easily masked by short-run factors, but over time they are crucial to more efficient flying.
The declines are enabled by two basic causes. OEMs continue to build better jets and engines, which need less maintenance and downtime. And OEMs, airlines and MROs grow smarter about how to perform maintenance.
The first cause should continue for newest twin-aisle aircraft: the Boeing 787 and Airbus A350. With more composite structures, these jets were designed to be maintenance-stingy.
But these new midsize widebodies will represent only 12% of new aircraft deliveries over the next 20 years, according to Boeing’s Current Market Outlook. By far the greatest portion of new aircraft— nearly three-fourths of deliveries—will be single-aisle jets. And for at least the near-midterm or more, this means new versions of the 737 and A320.
The 737MAX and A320neo were designed chiefly to help airlines reduce fuel burn with better engines, when fuel costs were skyrocketing and pressure to reduce emissions was on the horizon. But airframe and engine OEMs also have been paying attention to reliability and maintenance.
Both Boeing and Airbus have been working on two paths. First, they are exploiting experience with their veteran narrowbodies to develop better maintenance plans for existing and new types. And second, the new types have been designed to ease further maintenance burdens.
MAXs and Neos
For example, in 2015, Boeing implemented a new maintenance plan for both 737NGs and MAXs. The new plan calls for the first C check at three years and the first D check at nine years.
MAX customers also should benefit from improved health-monitoring and other enhancements, including an onboard maintenance function, maintenance task time extensions and a digital environmental control system. As customers become more comfortable with these technologies, Boeing expects fewer technical delays.
Boeing says early experience with the MAX is on track to meet or exceed its goal of 99.7% operational reliability, which is significantly higher than for A320s in the past, as acknowledged by Airbus. Some version of the 737 has been flying much longer than the A320, and that experience is evident.
With the Neo, Airbus is determined to close the A320’s historical gap with the 737 in both maintenance cost and reliability, according to Berthold Stegerer, head of aircraft operations marketing. Initially, airframe maintenance cost for the Neo is supposed to be 5% less than for the Ceo. The Neo has a centralized maintenance system, landing gear that are scheduled to be overhauled at 12 years, more advanced materials and composites, an electrical engine bleed-air system, a new fuel system with four feed pumps instead of six and longer-lasting LED lighting. Stegerer notes that both Ceos and Neos now also will go to 36 months between C checks, the same interval for NGs and MAXs. Heavy maintenance, however, will still have to be performed at six and 12 years.
Further, Airbus has launched a project to reduce airframe maintenance costs on the Neo another 10% by 2020. The Neo then will have a maintenance-free period of 10 days, an escalated frequency of A checks to 1,000 from 750 flight hours and have improved batteries, avionics ventilation and data-loading.
Stegerer says Airbus is on track to reduce maintenance costs by 15%. By 2017, 70% of Neo maintenance tasks had been either lengthened or deleted. And as further evidence that the goal will be reached, Stegerer cites the OEM’s success in reducing direct maintenance costs for A320ceos by 20% from 1990 to 2012.
Airbus reports operational reliability of 99.5% for Ceos delivered in the last six years. It is projecting the Neo will boost operational reliability to 99.7%, the same goal Boeing seeks for the MAX. So far, early Neos have been meeting this goal, Stegerer says. But this excludes Neos taken out of service for engine problems.
Leap and GTF
On the engine side, Airbus projects GE’s Leap engine will cost about as much to maintain as the CFM56 but sees Pratt & Whitney’s PW1100 geared turbofan (GTF) costing up to 15% less to service than the Ceo’s IAE V2527. Reduction in GTF costs stem from improved materials and composite fan blades, fewer materials and life-limited parts and dual-sourcing of parts. Indeed, the GTF has 2,000 fewer airfoils, six fewer stages and cooler engine core temperatures than V2500s. The GTF fan-drive gear system has no life-limited parts.
Development of those two new fuel-efficient engines, the Leap and GTF, is why the updated narrowbodies exist. Both powerplants have been performing well in fuel consumption but experienced some teething issues in early operations.
A forging problem that might cause high-pressure turbine rotor Stage 2 disk cracks in a few Leap-1As, used on some A320Neos, prompted CFM to recommend—and the FAA and EASA to mandate—inspections before 1,200 cycles or roughly 180-270 days of operation. And there were a few other production-quality questions about the Leap. Nevertheless, CFM argues the Leap has experienced a successful entry into service. By early December 2017, more than 150 aircraft of all types were flying with Leaps.
As 2017 ended, 24 operators on four continents had logged nearly a half-million flight hours and quarter-million flight cycles with Leap engines. The jets flew on 96% of available days, a performance that CFM calls, “simply unprecedented for a new engine.” Leap engines were expected to reach one million flight hours in the first quarter of 2018. And all this is being achieved while Leap cuts fuel and CO2 emissions by 15%, compared with the best preceding CFM engine.
Pratt puts the GTF’s fuel savings at 16% versus V2500 levels, but acknowledges there have been the sort of operational and durability issues common for new powerplants. These included what Pratt calls “nuisance faults” and longer-than-typical engine-start times. Both problems were overcome rapidly with software and minor hardware improvements, according to Pratt.
The GTF also experienced durability issues with combustor liners and the No. 3 carbon seal. These more serious problems caused a substantial number of premature removals of GTFs. Pratt reports it has developed and fully certified design modifications for the GTF on A320neos, which fix both combustor liner and carbon seal problems and will improve engine reliability and durability. The OEM started with the critical Neo GTFs, but plans to roll out similar modifications for GTFs on the Bombardier C Series and Embraer E2 jets by the middle of 2018.
Pratt aimed to produce 350-400 GTF engines in 2017 and more than double that count in 2018. Problems with the GTF caused a pause in orders in 2017, but Delta Air Lines’ booking for 100 A321neos powered by GTFs toward the end of the year provided a strong vote of confidence in Pratt’s product.
Southwest Airlines expects long-term maintenance costs on the MAX to be lower than for its 737NGs. The carrier notes that the MAX’s enhanced onboard network adds capabilities including advanced data collection at line speed, an onboard repository for loadable software and real-time data-processing. Overall, the MAX builds on the NG’s connectivity to provide real-time data about its systems to the ground. Additional tools report built-in test equipment and maintenance data so technicians can better assess dispatch limitations and maintenance actions.
From their entry into service in October 2017 through late December, Southwest’s MAXs experienced much less unscheduled maintenance than for the airline’s NGs, perhaps not surprising for new versus older aircraft. Southwest stresses that the MAX’s Leap engines were built for 99.98% dispatch reliability.
By December 2017, Lufthansa and its regional partners were operating 10 A320neos. Michael Lariviere, head of system engineering line maintenance at Lufthansa Technik says maintenance costs on Neos are supposed to be lower than on Ceos once the former are mature. However, he notes, “It is hard to predict when this will happen.” The hoped-for improvement should come from reduced airframe, component and line maintenance. Lariviere also expects Neos will also be more reliable, but “currently we cannot confirm this.”
He says both the Leaps and GTFs on Neos are still premature and presenting technical challenges requiring high maintenance efforts. “Both OEMs are working rigorously to improve the performance but still have some way to go,” Lariviere acknowledges.
Overall, short-term cautiousness but long-term optimism about reduced costs seem to be the rule, thoroughly justified by past experience.