Taking An Automotive Approach To AAM’s Aftermarket

parked Lilium aircraft
Automated pre-flight checks and predictive maintenance could speed up turnarounds for eVTOL operators.
Credit: Lilium

The commercial aviation MRO industry is a well-oiled machine, with maintenance providers, suppliers and airlines all working in tandem to ensure aircraft stay airworthy and off the ground as much as possible. For an emerging segment such as advanced air mobility (AAM) it would make sense to look toward the precedent of commercial aviation to build up the aftermarket needed to maintain these vehicles.

However, a typical electric vertical-takeoff-and-landing (eVTOL) vehicle features significantly fewer components, more complex battery technology and shorter stage lengths than most other commercial aircraft, so operators expect to fly fleets of these vehicles much more frequently. In some ways, the model of AAM operations seems more akin to the automotive industry—so will a mix of aftermarket standards from aviation and automotive maintenance be necessary to make operations viable?

At Aviation Week’s recent Aerospace Incubator conference in Miami, industry stakeholders discussed the challenges that lie ahead for establishing the aftermarket for AAM.

According to Carrie Kendrick, principal consultant for aerospace at SeaTec Consulting, some OEMs in the AAM segment have been kicking the can down the road when it comes to planning maintenance of their vehicles.

“One of the things we’ve noticed working with new OEMs is that they haven’t thought about what their services are going to look like yet,” Kendrick says. While SeaTec has noticed a trend of OEMs hoping to rely on systems providers and their MRO networks for maintenance, Kendrick thinks this may be short-sighted. “If these [eVTOLs] are going to be proliferated in the quantities of cars, then those types of networks maybe don’t support very well. There’s probably a logistics problem in between here that’s way bigger than just the fixing of parts.”

Kendrick asserts that AAM providers need to be thinking about maintenance services now—not closer to entry into service. She points out that many factors will need to be determined, such as which parties will be handling battery infrastructure and charging, determining inspection frequency, figuring out economies of scale for spare parts and maintenance staff, and how costs will be shared by operators and customers.

In comparing eVTOLs to cars, Kendrick notes that reliability and maintenance frequency are much different, even though many car owners drive their vehicles every day. For instance, despite daily use, owners do not check the oil daily. “What are the things that we’re going to need to do differently?” she asks, noting preflight inspections and cycles between maintenance checks as areas where maintenance will likely need to move closer to the automotive model of maintenance. “You’re going to have to treat it more like a car if you’re going to use it like a car,” she says.

Mujahid Abdulrahim, assistant professor in the University of Missouri-Kansas City’s Department of Civil and Mechanical Engineering, says that leveraging predictive maintenance data and automating maintenance processes will be critical in making the AAM operations model realistic.

eVTOLs battery charging station
Battery charge requirements, degradation and recycling are all areas that will impact MRO for eVTOLs. Credit: Eve

“There remains a huge difference between the casualness of driving a car compared to the seriousness of the preflight checks for an aircraft,” Abdulrahim says. “Traditional aviation is amazing but simply requires too much preparation to make rapid, short-haul transport possible at high volume. We will need to leverage a better model of the system performance, reliability and maintenance to realize the convenience promised in AAM.”

To streamline the maintenance processes needed for quick, frequent turnarounds, Abdulrahim suggests that the process of boarding an AAM aircraft should be more like catching a train or rideshare than flying commercially. “This means that the preflight checks should be largely automated, which should include a continuous monitoring of how critical systems degrade over time during and between flights,” he says. “All aircraft currently are subject to annual inspections, and those used commercially are subject to more frequent inspections based on hours in service. I suspect that some of these rules may be amended if there is evidence to show that system health monitoring can adequately determine the impending degradation or failure of a system component.”

Abdulrahim notes that many items on a traditional maintenance checklist—such as verifying correct functioning of motors, batteries, control surfaces, autopilots and sensors—could be automated. “I also think that a ‘preflight check’ will morph into a continuous modeling and monitoring of the subsystems,” he says. “Rather than a preflight check followed by an unmonitored flight, it will be an automated preflight check followed by a flight in which the subsystems are continuously being assessed against a predicted model of performance. Discrepancies can be noted and flagged during the flight, and that can be worked into the flight schedule to permit predictive maintenance to have parts ready and [airframe and powerplant technicians] available to minimize service disruptions.”

However, SeaTec’s Kendrick suggests that certifying maintenance staff to a commercial aviation level could prove a hindrance to the scale AAM operators hope to achieve. “We only have certain people today who can look at an aircraft or aircraft system and deem it acceptable. If people have to be that well-qualified, I think we need to be realistic,” she says. “Auto mechanics are not qualified to the same degree [as aircraft maintenance technicians]. How do we prove the system doesn’t need that level of inspection to be operating safely? We have to figure out how you’re going to have enough of those [highly trained] people to do the work.”

Even if operators can recruit enough qualified maintenance staff to perform the maintenance needed between aircraft turnarounds, Kendrick says operators will also run into hurdles of having enough spare parts at every vertiport location. “The volume of parts we’re talking about in terms of the longer-term fleet is way more than traditional aerospace is accustomed to dealing with,” Kendrick says. “We don’t know what the reliability is going to look like on these parts yet and if that’s going to match up [with scheduled maintenance cycles], so do we have the right order of magnitude for people and facilities to maintain these parts? Logistics is going to be a way bigger thing for the whole aircraft as well as the parts.”

The parts themselves may also be a hurdle in the face of supply chain challenges and competition from the automotive industry. “In a lot of ways, aviation is competing with automotive for the attention of engineers and raw material suppliers,” says Dana Jensen, senior industrial policy analyst for the U.S. Air Force. Citing battery suppliers as one potential example, he says. “The traditional big suppliers to automotive can’t be bothered, necessarily, or concerned with such a small industry.”

Several panelists at the Aerospace Incubator pointed out that other materials necessary for eVTOLs, such as carbon fiber, could be difficult to produce and source at the rates and volume needed for AAM. However, Jensen notes that certain sustainability initiatives could have the added benefit of providing some leeway.

technician with carbon fiber machine
Competition from the automotive industry for materials such as carbon fiber could challenge the AAM supply chain. Credit: John Kaemmerling/Joby Aviation

“There has been a lot of work done on recycling of batteries, and some of it is very promising, particularly in harvesting—not just the lithium, but all the metals out of batteries,” Jensen says. “To the extent that we can become more sustainable in terms of recycling, that’s going to help ameliorate some of the fragility we have in our supply chain while we’re still dependent on some of these refined minerals, such as cobalt, that are refined in places that may not see eye-to-eye with us geopolitically.”

One such supplier is Mobius Energy, which is developing electric-aircraft batteries that will be offered under a subscription model including maintenance, replacement and recycling. Its batteries are designed to be quick-charging and easy to maintain and swap. The startup told Aviation Week in September that it expects batteries to see 3-6 months of service in the high-frequency operation model expected for eVTOLs.

In addition to frequent operation, Mobius Energy cites regulatory requirements about battery life as part of the reason this life cycle is expected to be relatively short. “I believe regulators are considering mandatory retirement once the battery reaches 85% of original capacity,” said Jongwon “JP” Park, co-founder and chief strategy officer at Mobius Energy. “However, our customers are telling us that they plan to retire the battery even earlier, when it reaches 90% of original capacity, and replace it with a new battery to ensure safety and range.”

Vertiport and eVTOL operators are already thinking about the levels to which batteries will realistically need to be charged between flights.

“What percentage of the battery charge do you need to get airborne and how does that battery degrade over time?” says Joseph Alesia, senior vice president of business development at Ferrovial Airports, which is partnering with OEMs such as Vertical and Lilium to build global vertiport infrastructure. “Is 80% good enough for certification? Can you get airborne only with the ability to take 79% charge? What happens to that battery after it’s no longer reaching the charge that it was certified for? These are all questions that need to be addressed when you talk about infrastructure and how we can handle that.”

Reduced battery life could also become problematic for AAM operators planning to fly in hot and cold climates. “If you have suboptimal temperature conditions, you have to run heating and cooling or else you limit the life of the battery,” says the Air Force’s Jensen. “I hear a lot of people talking about operating in Alaska, but they don’t talk about heating infrastructure for the batteries that they’re storing, and that’s going to be a big deal.”

However, if AAM seeks a middle ground between aviation and automotive requirements—and regulators meet the industry halfway—there could be some wiggle room. Alesia suggests a comparison between battery charge and aircraft fuel tank levels. “When you’re getting from point A to point B in a traditional aircraft, you don’t always have full tanks,” he says. “I think the same can be said about battery-operated aircraft—it depends on the range and reserves.”

SeaTec’s Kendrick suggests predictive maintenance will ease some of the strain, noting that eVTOLs will have sensors to communicate battery level. This data, she says, will also reduce the stress of taking an eVTOL out of service compared to traditional aircraft.

“In the case of a fleet that could potentially be very large, maybe the decision to take that one item out of service is not as big a deal as taking a Boeing 787 out of service for a bigger airline. Maybe you automate some of those decisions,” she says, noting that an eVTOL needing maintenance within three days could also be scheduled to transport itself to a maintenance base. “I think that would be not just using the data but using thought processes we already have in order to use predictive maintenance to take a lot of the burden and a lot of the questions out of that system.” c

Lindsay Bjerregaard

Lindsay Bjerregaard is managing editor for Aviation Week’s MRO portfolio. Her coverage focuses on MRO technology, workforce, and product and service news for AviationWeek.com, Aviation Week Marketplace and Inside MRO.