Wheels and brakes maintenance is generally relatively simple, high-volume work, based on overhaul rather than repair.
Overhaul is also critical to companies offering components harvested from retired airframes, while the wider industry has grown to offer a variety of wheel and brake availability and overhaul programmes.
Wheels and brakes, along with lubricants, are among the most predictable of an airline’s maintenance items. Brakes, ironically, tend not to break, but they do wear, and the majority of brake maintenance is overhaul and the associated replacement of components that wear naturally every time braking is employed.
Confusingly, while a maintenance provider might replace an individual part within a brake unit during overhaul, the unit itself is generally considered as a single component.
Wheels are likely to suffer corrosion or damage from FOD. They should not be confused with tyres, although there is a necessary degree of overlap.
Like brakes, tyres wear naturally in use and a wheel may be removed and its tyre replaced a few times – typically between four and six, depending on aircraft type – before the wheel requires overhaul, assuming no issues are identified during the basic inspection that accompanies an intermediate tyre change.
Phil Randell, owner and accountable manager of World Aero, a UK-based specialist wheel and brake MRO provider, described the business. “Wheel and brake maintenance is always on an on-condition basis, there’s generally never any scheduled maintenance.
“Many people outside the business assume we’re busier during the winter when more aircraft are in heavy maintenance, but in fact, the opposite is true because if an aircraft’s tyres and brakes have life left, they won’t be disturbed during heavy checks. But when an aircraft is operating, if the tyres or brakes are worn out, they’ll be removed. Our work is therefore driven by aircraft utilisation.”
Brake and tyre inspection fall under the regular tasks included in line maintenance and, Randell says, once a unit becomes worn sufficient to require replacement.
“The brake unit or wheel is removed and a replacement fitted. The worn component then comes to us for refurbishment – wheel and brake maintenance is done off-wing (except for the 787, where on-wing maintenance of the aircraft’s electrical brake system is possible), and our main facility is not at an airport.
“On a modern, carbon brake we’d replace all the discs. They come as a ‘heat-pack assembly’ that replaces all the worn material. We also deal with leaks – brakes occasionally leak in service, and we also sometimes see leaks when we test units that come in for replacement worn heat-packs. With testing complete, we issue the unit with a release certificate, returning it to serviceable condition.”
World Aero’s airline clients typically pass wheel and brake units through the company on a regular rotation, while maintaining their stocks so that sufficient components are also available to service the fleet and provide airworthy spares.
It also works heavily with brokers managing maintenance on behalf of airlines and also with spares dealers, selling surplus or reclaimed stock.
“We’re an MRO; our primary role is to repair and overhaul other people’s wheels and brakes. We’re not about buying wheels and brakes and overhauling them as cheaply as possible for us to resell. Also, we respect that our dealer/broker customers are sending us units to overhaul for their sales stock and don’t then want to have to compete with us in the sales market. Consequently, end-users purchasing a unit with World Aero certification know it has been overhauled to a standard, rather than to a price.”
While World Aero works high volumes for large airlines, Randell is also proud of its capability to accommodate ad hoc requirements. “Our ability to do that is inherent in our workshop layout and the processes involved; we’re able to provide the same standards and speed of service to our one-off customers as we do to our regulars.”
He declines to elaborate on the key processes and working arrangements, but notes: “Although we have a large customer spread, it’s important not to turn away single jobs – they’re something other MROs often struggle with.”
Specialising in aircraft end of life services, Caerphilly, Wales-based AerFin considers overhauled brakes among the most common assets harvested from any relatively young airframe it breaks down.
Richard Jowett, vice president purchasing and programs, explains: “Wheels and brakes are rotable parts, meaning they can be rebuilt, overhauled, returned to inventory and used to maintain aircraft. From an aircraft tear-down perspective, it’s crucial to know the history of the wheel and brake so the work scope, usage and value of the components can be determined.
“This will influence the decision to remove the unit from the aircraft ‘on condition’ or to route it to a workshop for refurbishment. As part of the evaluation process of a brake, we measure the unit’s remaining life, which helps establish its value. It will then either be removed and sold in AR [as removed] condition, or go to a workshop for OH [overhaul].
“In both instances, we retain the remaining carbon heat-pack [most brakes use carbon, not steel], as this also helps determine its sale value. Customers are most interested in the remaining life, since this can be used to calculate and predict the expected number of landings they can achieve from a unit before having to remove it and install a full life heat-pack.
“We may decide, depending on the remaining life, to install a 100 per cent heat-pack in the unit there and then, or to sell or exchange it in an OH condition. When it comes to wheels, in most cases we remove the wheel from the aircraft and send it straight to an MRO shop for overhaul, before trading it without the tyre.
“This is popular with airlines, since it offers them the opportunity to select their tyre of choice, to be fitted by AerFin or their appointed workshop. Surplus tyres hold their value too; we keep them in our inventory for resale once they’re been overhauled and retreaded.”
Since complete records for the wheel and brake components AerFin takes in are seldom available, Jowett says quality and safety are guaranteed by other means.
“We usually route the wheel and brake unit to an MRO for overhaul. We then resell the component in a serviceable condition, but it must be complete with trace documentation back to its last operator/owner and a non-incident statement [NIS]. Overhaul generates a history and a workshop report to add to the trace documentation and NIS received with the components. A full trail, from original delivery, is ‘nice to have, but certainly not essential’, he says.
Programmes and packages
Headquartered in Copenhagen, TP Aerospace is a global supplier of wheels and brakes, offering exchange and cost-per-landing programmes, and bespoke support packages. It maintains and services wheels and brakes through its own facilities, a network of subsidiaries and wholly owned subsidiaries of those organisations. It’s a challenging business that’s carefully controlled to ensure parts are always available while simultaneously avoiding overstock.
Frank Rott, TP Aerospace Global COO and accountable manager EASA Part 145, describes the company’s exchange and cost-per-landing programmes:
“In general, alongside working on their wheel and brake assets, we offer a complete package, including a collection of unserviceable units from their locations, tyre changes, repair or overhaul at our facility, and redelivery, directly into customer storage if they prefer. Our programmes include a pre-defined pool-size, agreed on both sides and ensuring the customer always has sufficient wheels and brakes for their fleet.
“Maintaining stock at suitable levels is a challenge, but we work hard to ensure our provision matches customer requirements. We support more than 200 wheel and brake part numbers around the world, as well as tyres.
“We’ve established our own database that helps us purchase tyres and spare parts at the right time so that we never run our stock down to zero. We also have contracts with global suppliers, strengthening our position in the market and winning the best prices for our customers. So, we always have sufficient spares in stock, and we’re always happy to support ad hoc customers, too.”
TP Aerospace assigns dedicated programme managers to its regular customers. They liaise closely with the client, keeping a detailed watch on their operation to ensure TP’s stocks and service availability keep pace. Where service is offered by a subsidiary, or even the subsidiary of a subsidiary, it is essential for TP Aerospace that its high service standards are guaranteed, and that assurance is a responsibility that falls to Rott.
“We have global customers who expect to receive the same service worldwide. Our management set up is therefore also global, and I work to ensure we all have the same standards, the same tools, processes and procedures, training, and access to the same information, at all times. Taking care of our customers comes down to a great team effort across the organisation.”
While TP Aerospace carefully manages and optimises its wheel and brake stocks, AerFin aims to keep stock at high levels wherever possible.
“Typically, we compile a stock of components so we’re ready to meet any number of customer requirements,” Jowett says. “We’re seeing an increase in demand for wheel and brake components. Take Cathay Pacific’s fleet of A340s, which we retired in 2015, as an example – we successfully sold the inventory before aircraft tear-down had even begun.
“Wheels and brakes are among the few items whose sale you can guarantee. They’re key components an airline has to purchase or have supplied through a CPAL [charge-per-aircraft-landing] programme, meaning we sell directly to the airlines and, in some cases, to wheel and brake service providers supporting CPAL programmes.
“Depending on the product type and value of the assets though, we may route components for overhaul and hold serviceable inventory as exchanges to support our own airline programmes.”
Wheel and brake components clearly play a significant role in AerFin’s business, and the company has amassed a considerable stock.
However, it’s notable that equipment from some aircraft types is more desirable than others, Jowett notes: “We have a focus on the Embraer E-Jet. Through our acquisition of Saudia’s fleet of 15 E170LRs we’ve built up a substantial portfolio of wheel and brake inventory. Securing this volume and quality of product was key to delivering our strategy to become a single-source supplier for the aircraft, offering operators the lowest possible E-Jet spares and maintenance costs.
“Under the contracts arm of our business, we’re also supporting one of Europe’s largest leisure operators with a wheel and brake service contract on its Dreamliner fleet. Through our significant 787 wheel and brake inventory, we guarantee them availability and stock, while reducing turnaround time and unexpected high repair costs for their wheels and brakes.”
“Wheels,” World Aero’s Phil Randell explains, “tend to suffer most from corrosion and/or cracking. These defects are not normally seen in service, but discovered when a wheel comes in for a tyre change, so our wheel work is driven by tyre wear. When we change a tyre, we also do a wheel inspection, including cleaning, basic NDT and regreasing the bearings.
“But when overhaul is required, we remove all the paint, taking it back to bare metal, perform full crack detection for pretty much all the wheel parts, a full measurement inspection, and then a very detailed visual inspection, followed by repainting and rebuilding. It’s during this more detailed work that we find the types of issue a simple tyre change would miss.”
Airliner wheel and brakes are by nature relatively large, heavy items, with brake units being particularly dense. It means that even the seemingly simple logistics involved in moving them from the aircraft to a workshop requires careful consideration, especially for health and safety.
EasyJet’s large fleet, for example, consumes considerable numbers of wheels and brake units on a daily basis, and while their refurbishment doesn’t come under its logistics contract with AJW Group, the airline uses the company’s transport capability to move them between airports and its preferred MRO, and between line stations, as required.
Randell says the largest brake unit World Aero regularly handles is from the A330, weighing around 130kg.
“Older-generation steel brakes were even heavier – often in excess of 200kg. We employ a great deal of heavy lifting equipment, but as soon as disassembly begins, the individual components are not overly heavy – around 15kg at most. Fully assembled though, the unit is very heavy and valuable. So, we continue to develop lifting systems to move brakes around the workshop safely and efficiently.”
According to World Aero’s website, the company is capable of processing as many as 130 units per week. Since ‘unit’ is an industry term for an individual wheel or brake assembly, this seems an extraordinary amount of work. “It is,” Randell agrees, “and it’s a rate that surprises many people when they visit us.
“Being privately owned, without the complexities of a large corporate structure, we’ve set ourselves up through investment in equipment, facilities and training, to be dedicated to efficient wheel and brake maintenance. There’s very little that surprises us, the work tends to be similar irrespective of manufacturer or operator.”