Airline tires take a beating. When a tire reaches its service limit, maintenance technicians remove the entire wheel and replace it; the same for brakes. So, what happens to the old wheels, tires, and brakes? They certainly aren’t thrown away. Technicians send old wheels and brakes to a Wheel & Brake Shop for overhaul.
This is the second of two articles about aircraft wheels. Be sure to read the first article: Aircraft Wheels for more information about airliner wheels and tires!
Most airlines have their own wheel and brake shops — large carriers have several shops located around their systems. Smaller airlines may use a vendor for tire and brake services.
The UPS Airlines Wheel and Brake Shop in Louisville, KY provides wheel and brake services for its North and South America networks. I had the pleasure of visiting the shop to see what they do. It’s one of the most fascinating behind-the-scenes tours I’ve experienced.
Located in a nondescript warehouse, the facility operates a 9 hour shift, 5 days a week. It’s a busy shift. In 2018, the shop overhauled over 8,000 wheels.
Wheel Disassembly
Dozens of worn wheel assemblies arrive by air and ground each morning from as far away as Anchorage, Alaska and Santiago, Chile. Each wheel begins its visit at the disassembly area.
Wheels are first depressurized of any remaining nitrogen. Heat generated from takeoffs and landings fuse the tire beads to the wheel rims. The Bead Breaker is a hydraulic press that squeezes the 2 sides of the tire together to separate the tire beads from the rim. They become unstuck with a satisfying pop.
Two technicians raise the wheel to a comfortable work height and remove 20 or so nuts and bolts that hold the wheel hubs together. Wheels are separated and removed from the tire.
Bead Breaker: Unsticks wheel hub from tire bead 
Wheel raised on lift 
Hub bolts removed 
Wheel halves separated 
Hub ready for cleaning 
Tire bead
Farewell Old Tires!
Worn out tires are shipped to the manufacturer to be retread or recycled. A tire carcass (also called a casing) can be retread as many as 16 times. Airlines often impose lower retread limits to enhance safety. UPS retreads their main tires between 3 and 9 times, depending on aircraft and tire type. UPS tracks tire carcasses carefully to assure it receives the very same tires back from the retread facility.
Take a Bath
After disassembly, technicians place wheel halves and their hardware in an automated parts washing system. The washer looks like a large restaurant dishwasher and uses environmentally friendly solvents. Parts exiting the wash are sparkling clean and look nearly new.
Wheel and parts washer 
Clean wheel halves ready for inspection
Inspection
When a wheel visits the shop, it receives a minor or major inspection as required by the manufacturer.
Minor Inspection
Most visits require wheel components to have a minor inspection. After cleaning, technicians visually inspect all parts for visible wear or cracks.
Major Inspection
Wheel parts undergo a major inspection at regular intervals. After cleaning, technicians subject all parts (wheel hubs, nuts, and bolts) to eddy current and ultrasonic testing. The test equipment can detect hidden and microscopic deformities and cracks in the metal. Any component that is less than perfect is scrapped and the metal recycled.
Aircraft wheel eddy current tester/scanner 
Eddy current flaw detector
Nothing is left to chance. Even the bolts holding the wheels halves together are ultrasonically tested for defects.
Ultrasonic Wheel Bolt Inspection. Bolt highlighted by arrow 
Ultrasonic Wheel Bolt Inspection
Alodine Coating Station
The Alodine Coating Station gives aluminum alloy wheels a protective coating to inhibit corrosion. Alodine coating is also known as chromate conversion coating – the metal surface is chemically transformed into a protective layer. I’m no expert on this stuff; I learned a bit about it here.
Wheel and Tire Assembly
After cleaning and inspection, it’s time to reassemble the wheels with fresh tires.
A TPMS (Tire Pressure Monitoring System) sensor (MD-11 and 747-8 main tires) and over pressure relief valve are installed in the outer wheel rim. Three fusible thermal plugs are screwed into holes on the inside of the wheel rim.
Learn more about these safety devices in the previous article: Aircraft Wheels
Over Pressure Relief Valve 
TPMS sensor installed 
Fusible plug mounting hole 
Fusible plug and over pressure relief valve
After the new tire is pushed onto the inboard hub, the assembly is laid on its side so the smaller outer hub can be positioned over the bolts. Techs hand thread the nuts, then snug them up with a pneumatic wrench. A large manual torque wrench is used to achieve final torque to factory specifications.
The following series of photos show the assembly process for a 747-8 main wheel.
Tire positioned next to hub 
Tire pushed onto hub 
Wheel lowered to horizontal 
Ready for the outer hub 
Outer hub positioned over bolts 
Nuts threaded onto bolts 
Pneumatic wrench tightens bolts 
Final tightening with torque wrench 
Completed wheel
Tire Inflation
The wheel and brake shop has a large liquid nitrogen tank outside the facility. Nitrogen pressure is reduced to 300 psi before entering the building and distributed to three tire filling cages.
Each wheel is rolled into a filling cage, nitrogen hose connected to the valve stem, and the cage is closed. A digital tire inflator accurately fills the tire to the proper pressure.
Why use a cage? Aircraft tires are pressurized to over 200 psi. If a mistake was made during assembly, or if the tire inflation system malfunctions, the results could be catastrophic.
The digital inflator pressurizes the tires slowly. It takes 30 minutes to an hour for a main wheel to reach full pressure.
Three tire inflation cages 
Tire is rolled into a cage 
Nitrogen hose connected to valve stem 
Digital inflation controller – Select desired pressure. Actual pressure displayed below
Wheel Bearings
Shop technicians disassemble, clean, inspect, and rebuild wheel bearings. After new bearings are installed in pressurized wheels, protective shipping covers are attached to protect the bearings and rims from damage.
Bearings being assembled 
Overhauled bearings ready for installation 
Freshly overhauled, assembled wheel 
Completed wheels in the warehouse
Brakes Are Overhauled
Line technicians inspect aircraft brakes every day. Brake assemblies on a UPS 767 last about 1900 cycles, so they aren’t changed nearly as often as tires.
When a brake assembly reaches its service limit, a technician removes the wheel, pulls off the brake, and replaces it with a new one. Like wheels, fresh brake assemblies are kept on hand at scheduled UPS destinations.
Worn brake assemblies awaiting overhaul 
Brakes ready for disassembly
Worn brake assemblies from UPS aircraft make their way to the UPS Tire & Brake Shop in Louisville. The brakes go through a similar process as wheels. Old assemblies are taken apart and cleaned. Parts that are warn beyond limits are discarded and recycled. Serviceable parts undergo thorough visual and metallurgical testing.
Clean brake cores ready for rotor/stator stack 
Overhaul of a 747-8 piston brake actuator 
Overhauled 767 brake assemblies ready for shipment
Wheel & Brake Shop techs reassemble the inspected brake assemblies and ship them back to UPS aircraft destinations worldwide where aircraft mechanics will install them as needed.
The Circle of Life (for wheels & brakes)
The journey begins all over again at airports throughout the UPS system. The photo above shows wheels worn to service limits in Anchorage, Alaska, awaiting shipment back to the Wheel & Brake Shop in Louisville.
I’d to give a very special thank you to the staff of the UPS Airlines Wheel & Brake Shop and UPS Airlines Public Relations for granting me access to this fascinating place!
Really fine, detailed reporting here, Captain! As a mechanic in a much earlier career, I appreciate what the men and women of UPS shops do – and how clean that Wheel & Brake shop was, for what it does. Awesome stuff!
Thank you! The shop was really interesting.
There must be massive wear and pressure on the wheels and brakes, guessing they get really hot. Have you ever had a tire blow out on the runway? Interesting they still torque by hand. Great photos Thanks.
Herb
Tire blow outs are extremely rare due to the careful maintenance tires and wheels are given.
Thank you very much for the article, it was very interesting. Does UPS have any Dreamliners, if so can you do a tour of one for us?
I’m not aware of any plans to build a freighter variant of the 787.
Interesting article, must have been a lot of fun watching the process..
Thank you so much I find your articles so interesting.
Thank you!
Capt.Ken …. could clarify the term ” cycle ” ?
A cycle is one takeoff and landing. Or one flight.
I don’t know if it’s still the case, but in the 70s, at least part of the USAF was recycling jet fighter front tires, by specifying wheels that allowed their jeeps to use tires retired from the jets: The tires were only allowed a limited number of total landings;instead of retreading or discarding them. they were re-purposed.
(I saw this at Loring AFB, but do not know if it was just there, or force-wide).
Hey Ken,
a very intresting and great article. althoug i got a question i work for a aircraft tire retread plant and we do balance the tires before we molding the new tire compound. Thats why we place red dots to indicate where the balance point is located. i thougt this was crucial for the wheel and brake shop to align the tire on the wheel. But i can’t find anything about it in your article. So my question is does the wheel and brake shop need a in balance tire before they can place it on the wheel?
Immanuel
Hello Immanuel,
I recall the tour guide telling me something about aligning the balance point on the wheel but I don’t remember the procedure.
Thanks for reading!
Ken
Hi,
When an aircraft wheel gets to the end of its life, what do the companies do with them?
I’m looking for a few wheels for an application at our shop. We need the bolt together style wheels for our 49×17 tires. I am finding it difficult to find these
Any help would be appreciated.
I believe the wheels are recycled. I don’t know how you could acquire one.
Hi!
This is a very random question but I was wondering if you could give an estimate on how large a wheels and brakes shop usually in floor area (metric or english)? We are doing a research on setting up a wheels and brakes shop and we need to estimate the rent, etc. The average size of the facility itself would a big help. Thank you.
I don’t have the expertise necessary to answer your question.
Hi Ana,
I have expertise on setting up wheel and brake shops available.
Feel free to contact me at my email- meleciojav@gmail.com.
I’ll help as best as I can!
Hi Ken,
This article was great!
Thank you for your insights into the aviation industry.
It’s awesome gaining the perspective of a pilot 🙂
-Javi
Hi Ken
I have just read your article from Kenya and I found the information contained therein to be of great use particularly to those who are contemplating of setting up a wheels and brakes shop. The tour give a preview of what one is expected to encounter. Not a walk in the park.
Due to the size of the facility, I would have expected the eddy current testing of the wheel hubs to be carried out by using automatic eddy current scanner.
In case you do a similar tour, please include the pressure testing rig for brakes after they are assembled.
Don’t stop here give us some more articles.
James Kamau
Thank you for the kind words. The information in the article is the extent of my knowledge about aircraft wheels and brakes. I’m sure there are more comprehensive resources out there.
Hello Ken,
Hope you are great. I would like to ask you about rim nuts and washers.
There is 20 nuts in the pictures, I wonder what kind of nuts used on this rim?
Additionally, what kind of nuts are used in aircraft rim?
If you answer my question ı would be very apricate.
I have no idea. You would need to ask someone more familiar with the process.