Wheel & Brake Repair and Overhaul

By Charlotte Adams

As operators know, wheels and brakes need attention—and plenty of it. The wheels and tires take the brunt of a landing. And bringing a large aircraft to a stop requires the brakes to absorb enormous amounts of heat. But these lowly elements of sleek flying machines can wreak havoc with an aircraft if they are not properly looked after.
Life is hard for wheels and brakes at the best of times. But operational and environmental conditions can also take a toll. Additional wear or damage can result from extended taxiing, short field or hard landings, and exposure to extreme operational conditions and elements, such as rejected takeoffs, inadequate tire pressure, and overheated brakes, explains Steve Kelly, director of product repair services for Aviall, now a unit of Boeing.
Tire and brake wear can differ, depending on factors in a customer’s operation, such as climate and runway conditions and landing procedures, says Hilde Pilkuhn-Alizadeh, section manager in the Wheels & Brakes and Cabin Electronics business unit, with Lufthansa Technik (LHT) Aircraft Component Services. Oxidation of heat stacks is a problem, especially in cold winters, due to extensive use of runway deicing fluid, she adds.

Market Impressions
That’s why wheel and brake repair and overhaul (R&O) is a steady business. In Europe the commercial wheel and brake MRO market is estimated to be worth some $800 million, growing at two to four percent per year, according to LHT.

AFIKLMEM_WheelsBrakes (4)  In the U.S. there are signs that the wheel and brake R&O market may be in a slow-growth period. In Honeywell’s view most airlines are controlling costs and not investing in fleet expansion. Instead, they are retiring older aircraft and replacing them with newer, more efficient models to reduce fuel costs. In general, airlines are requesting shorter-term contracts, Honeywell says. The focus is on reducing fuel consumption and costs.
Dallas Centerline, a Texas-based repair station, takes a more somber view. David Kirby, vice president and general manager, thinks the stateside R&O market seems to be shrinking “due to early retirement of aircraft types that are not as efficient to operate and the enticing deals manufacturers are making to sell the latest models.” Military business has been affected by the sequester and by the emergence of “larger and larger consortiums of service providers [that focus] exclusively [on] the military market,” he adds.

OEM Impact
Like almost every other area of the commercial aftermarket, the wheel and brake sector is seeing increased activity by original equipment manufacturers (OEMs). (This seems to be less of a trend in corporate aviation.) Companies like Goodrich (now UTC Aerospace Systems) and Honeywell are major players. LHT’s Pilkuhn-Alizadeh estimates that some 40 percent of the OEMs promote their own workshops, while 60 percent concentrate on selling material to MRO providers.
But Kirby, of Dallas Centerline, sees the growing presence of the OEMs in the wheel and brake R&O market as a negative for competition, citing the “very destructive policy” on obtaining instructions for continued airworthiness (ICA) and the difficulty of obtaining OEM parts at competitive prices. Kirby also says that OEMs, when they are the sole source of piece parts, make it difficult to use non-OEM, PMA parts under OEM warranties.

Honeywell sees it differently. Competition will always exist in any healthy market, the OEM says. It stresses partnering with the right businesses as a key to success. But the company notes that “substantial costs are associated with the entry to market and substantiation of a product [in] a new fleet.” And, while it’s nothing new for OEMs to try to recoup product development costs in the aftermarket, the company also sees an upside: “If a wheel and brake MRO is also an OEM of the product they service, then there are material cost savings.”
Honeywell’s wheel and brake MRO Web site asserts that the company is the No. 1 independent landing systems R&O business in the industry. The site, http://www.honeywell.com/sites/aero/MRO-Services.htm, also says that the OEM, through its R&O network and distribution centers, supports more than 3,000 aircraft, with the capability to maintain other manufacturers, as well as its own, wheel and brake equipment.

Honeywell service packages range from a basic time and material program to an all-inclusive power-by-the-hour-type cost per aircraft landing (CPAL) arrangement. Honeywell’s network supports Boeing and Airbus aircraft, as well as Bombardier CRJs and Embraer ERJs. The company also calls attention to its use of TAFA thermal spray for repairs that involve adding material (metal) to a part.

Airline MROs
Lufthansa Technik is a major player in wheel and brake R&O, with almost 900 aircraft under contract, mainly European customers but also carriers from Africa, Russia and Asia. Apart from Lufthansa itself, customers mainly come from the low-cost carrier market, but also include cargo, leisure and regional operators, Pilkuhn-Alizadeh says. Usually customers have a long-term agreement (5-10 years) with LHT and send all their wheels and brakes to the shops in Frankfurt, she says. The MRO’s main price model is a rate per landing (cycle), but LHT also offers fixed price per overhaul or repair and time-and-material models.
The German MRO provides loans and AOG support, depending on availability, and offers services such as repair, overhaul and pooling. LHT overhauls more than 20,000 wheels annually in Frankfurt, according to its Web site, http://www.lufthansa-technik.com/wheels-brakes. It also overhauls about 3,000 brake systems a year, including both steel and carbon varieties, the portal states. Among its services, LHT can rework structural parts and rotor discs to reduce scrap rates and material costs, according to the site. The unit works on the wheels and brakes of all types of Boeing and Airbus aircraft.
Lufthansa Technik also notes a strong correlation between demand and time of year. LHT sees twice the number of wheels in the workshop in the summer than in the winter. The number of consumable parts is low for the wheels, but high for brakes, Pilkuhn-Alizadeh adds. With more than 50 years of experience in the maintenance of wheels and brakes, LHT has developed several repair processes for structural parts which lead to material use rates considerably below industry average, she says.

LHT in general puts a lot of emphasis on Lean production and—in its new joint venture with McKinsey—has even built up consulting for third parties in process optimization and “transformation” implementation. Wheel and brake services, especially, with their large number of workshop events per year, lend themselves to the “industrialization of processes and economies of scale,” Pilkuhn-Alizadeh says. LHT’s wheel and brake services are set up as a Lean-production, she adds. “Flow principles, performance management, workshop design, material consumption analysis and workplace layout are examples which target cost and TAT [turnaround time] reduction to lessen the cost spiral for customers.”

Air France Industries KLM Engineering & Maintenance (AFI KLM E&M) wheel repair and overhaul hubs are located at the Charles de Gaulle (CDG) and Orly airports near Paris and at Amsterdam Schiphol. The shops perform some 17,000 tire changes and wheel repairs annually on aircraft such as the E190, Boeing 737 family, A320 family, A330, A340, A380, B747, MD11 and B777, says Philippe Servant, product line manager for wheels, tires and oxygen components at CDG.

HoneywellMount pics 001The shops are organized and built around processes such as Lean and Six Sigma. Using these methods, Servant’s unit has cut the time to change tires and repair wheels in half—from 10 days to five days, he says. Every week the shop measures performance parameters such as work flow, inventory, turnaround time and quality of service, he says. It also uses Six Sigma to identify and remove the causes of defects and errors in its MRO processes. The Paris shops were certified to the ISO 9001 quality standard in June 2007, he says.

Each time a wheel is removed to change a tire, technicians inspect it for possible problems, Servant says. After a wheel has been removed three times (from 1,500 to 2,500 cycles, depending on the wheel type), an overhaul is performed on it even though the manufacturer’s limit may not have been reached, he says.

The AFI KLM E&M wheel shops offer several pricing options. Among these are fixed price per flight hour, cost per aircraft landing , fixed-price repairs and various levels of exchanges. Emergency AOG service involves a response within an hour of the request and the provision of a wheel from the delivery center within four hours of the request. Standard exchange entails a response within four hours of the request and the dispatch of a wheel from the delivery center within 24 hours of the request.

CRMA, an AFI KLM E&M subsidiary, repairs steel and carbon brakes for the MRO, covering the A320, A330, A340, 747 and 777. This repair station near Paris repairs or overhauls more than 1,400 brakes per year. CRMA also has developed new support capability for A380 carbon brakes for AFI KLM E&M, and the unit repaired its first A380 brake in April 2013.

Parts Suppliers
Through networks of repair stations, parts suppliers are also players in the wheel and brake repair and overhaul market. AAR works on a wide range of wheel and brake systems, including commercial, regional and military aircraft, says Alex Lara, product line manager for the company’s Wheel and Brake Services unit. AAR has a major facility in Miami.

Aviall operates seven repair stations for wheel and brake services across the United States. It provides OEM-authorized maintenance and overhaul services such as inspection, repair, overhaul, parts replacement, repainting, assembly and functional test. The company also maintains a large rotable exchange pool of brake assemblies for a wide array of aircraft, Kelly says. Exchange brakes are shipped the same day they are ordered.
Aviall notes that certain items are designed to wear out and be replaced. The replacement parts include expendable/consumable items such as elastomeric seals and fasteners. Other items are reusable as long as they meet specifications. However, “the opportunities to perform repairs on items that do not meet specifications are very limited with wheels and brakes since they are such critical safety items,” Kelly explains. For example, superficial damage, such as a surface scratch, to a wheel half or brake housing can be repaired as long as the structural integrity of the item can be confirmed by non-destructive testing. Aviall says its close working relationship with the OEMs and its “sharing [of] in-the-field data” have resulted in “many component life-extending repairs.”

Aviall replaces wheel and brake parts such as seals, wear pads and rivets at each overhaul, Kelly says. “Other major components, such as brake frame housings and torque tubes, and wheel halves, are inspected and reused if they meet OEM specifications, [while] certain wear items, such as wheel bearings and brake stators, are replaced on condition.” Further, brake work such as “torque tubes requiring weld and plating repairs, stator, back plate, and pressure plate repairs, along with axle bore and bushing repairs can affect brake turn times,” he says.

Corporate Aviation
Sidebar1BCorporate aviation presents a slightly different picture since these aircraft aren’t as heavily used as commercial jets. West Star Aviation, a privately owned MRO/FBO that operates a network of repair stations is a good example. West Star has a sizable wheel and landing gear business, but works in many other areas, such as airframe repair and maintenance, engine repair and maintenance, major modifications, and avionics installations and repair. The company’s Grand Junction, Colo., site sees 1,000 sets of wheels a year, according to Steve Goede, Accessories Department manager there.

There’s a big difference between commercial and corporate aviation in wheel upkeep, Goede explains. In commercial it’s, “fly, fly, fly, fly” so the cores are going to come in for repair or overhaul fairly frequently, as required by their maintenance manuals or by normal wear and tear. In business aviation events are less frequent because these aircraft are not in the air so much of the time. That said, however, many corporate operators want their wheels overhauled each time the tires are changed, he says. After all, the CEO or some top company officer is in the plane.

Overhauls are fairly involved and make use of a range of different nondestructive testing (NDT) technologies. First the wheels are removed, disassembled, cleaned, stripped of paint, and visually inspected for wear, cracks and corrosion. A caliper is used, for example, to measure small areas, such as the diameters of bolt holes, for dimensional wear. Then, depending on the type of wheel involved, various forms of NDT can be employed. Any repairs that can be made are done at this time, and then the parts are painted and reassembled, and new tires are mounted and leak-checked, after which the wheels are returned to service or released to the customer.

West Star uses any of three types of NDT methods in overhauls—eddy current, dye penetrant and mag (magnetic) particle. The choice of technology depends on the makeup of the wheel assembly and the requirements of the manufacturer’s component maintenance manual although the shop routinely conducts an eddy current examination of the wheel bead seat—the flat area of the wheel that the bead of the tire rests against—each time it changes the tires.

Eddy current can be used to detect cracks that are not visible to the eye, Goede says. But even if only a small crack is found in a wheel, the wheel is typically rejected, he says. Dye penetrant involves dipping a wheel in penetrant, processing it via a rinse bath, and air drying it in a circulating oven, after which a developer is applied. Then the wheel is examined under an ultraviolet light. This method is used to detect cracks and impurities. Mag particle is used for examining the bolts for cracks, impurities or other flaws. It involves magnetizing the bolt while examining it under ultraviolet light. Both the eddy current and mag particle procedures involve inducing a temporary magnetic field in the components under test.

Brakes: Steel, Carbon or Electric?
The entire industry is leaning towards carbon brakes, Honeywell executives assert. Lufthansa Technik also sees a trend towards carbon brakes, as the mean time between repairs (MTBR) for carbon brakes is 1,500-2,000 cycles, compared with some 1,100 cycles for steel brakes. Carbon brakes, especially Messier-Bugatti carbon brakes, have overtaken the industry, asserts David Kirby, vice president and general manager of Dallas Centerline, a Texas-based repair station.

Carbon brakes are popular where weight reduction is crucial, adds Steve Kelly, director of product repair services for Aviall, but steel brakes will continue to have a place because they are significantly lower in cost.

“One of the most intriguing new technologies is the ‘electric brake,’” where electric actuators operate the brake in lieu of hydraulics, Kelly says. This upcoming development will add weight savings, as well, Kirby notes. But the technology is still new in the commercial world. The 787 is the first airliner to fly electrically actuated brakes. Boeing boasts that this system, developed by Goodrich, reduces the complexity of the component and increases its dispatchability compared with hydraulic brake systems.

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