From the Flight Deck

Filming a tire change


I've been approached by a production company to possibly produce various aviation documentaries on the many aspects of aviation. But before we can go forward with the idea, we had to make a "pilot" to entice potential buyers.

We picked two ideas to help promote the concept, "how pilots land in fog" and "changing an aircraft tire." We spent three hours in the simulator late one night and recently filmed an Airbus 319 getting a tire changed. The maintenance department were more than willing to help with the promo.

I mustered up some old articles on airplane tires. Here's some interesting facts found in these enRoute articles.

This June fans in Montreal will again see new layers of rubber on the track from the tires of the Grand Prix racers. Yet the racing term, ‘Lay some rubber’, shares similarity with that of a landing airplane when the cloud of bluish smoke appears as the tires touch the runway. Aircraft tires are as an important interface between the plane and the runway as racing tires are between the car and the track.

When was the last time you walked around your car to check the condition of your tires? The tires on Air Canada’s fleet are constantly under scrutiny either by maintenance personnel or by the pilot during his/her ‘walk around’. One such maintenance person is Constance Von Muehlen, manager of the three tire and wheel shops in Toronto, Montreal and Vancouver. She knows lots about aircraft upkeep, as she was a maintenance officer and test pilot on helicopters for the U.S army. She tells me tires have an average life of 300 to 450 landings for the main wheels and 200 to 350 landings for a nose wheel. Some tires might stay on much longer: up to 600 landings while others may be removed at 50. Every tire has its own history. Goodyear supplies the entire fleet with tires and decides which tire will be re-treaded and which will be discarded via a closely monitored serial number. Every airplane varies as to the tolerance. The Boeing 767 allows the ‘mains’ to be re-treaded five to six times whereas the RJ doesn’t allow any.

The average cost of an airbus 340 tire is over CDN $2100 with the main wheel (rim and tire) weighing 230 kgs. The weight, price and size vary substantially with that of a car but the actual changing of one is similar. Firstly, the bolts that hold the wheel in place are loosened before the aircraft is jacked up with the plane properly secured with wheel chalks. (Something many forget when changing a car tire.) A high powered jack, capable of lifting a jumbo jet, lifts the plane the required height to remove the tire. A clever device then aids the mechanics to offload the old tire and on load the new tire. This all takes about twenty minutes about the same time you would take. However, this pales in comparison with the eight seconds it takes to change four tires on a formula one car.

Unlike your car tire, an aircraft tire is filled with nitrogen instead of air for various reasons. Air contains moisture and would freeze at altitude with the average temperature being minus 56 Celsius. Nitrogen doesn’t form a liquid until minus 173 and contains little to no moisture. As mentioned tires are subject to tremendous forces on landing when they must accelerate very quickly. They may heat up quickly and with air containing approximately 20 percent oxygen may pose a fire threat. This is virtually eliminated when using nitrogen. It also prolongs the tire life by not allowing oxidation and rust formation inside the wheel.

Also located on the wheel assembly are the brakes. They are hydraulically actuated from very strong hydraulic systems. The brake pads are either metal or carbon, but Constance mentions most are being replaced by carbon discs. Carbon brakes are more durable but much pricier. Two pedals in front of each pilot control the brakes, but where they differ from a car is; there is a left and right set of brakes. The wheel assembly also includes anti-skid devices. The principal is similar to ABS (automated braking system) found on cars, preventing the tire to lock up during braking.

Another brake, the parking brake, similar to your car, is also found in aircraft. The parking brake switch is wired to the data link system that transmits the out/in times at the gate to within the minute.

Sometimes during take off there is a repetitive bumping sound which some may think is a flat tire. Not to worry, it’s just the nose wheel running over the centerline lighting embedded in the runway. The nose wheel is the only wheel that actually moves from side to side and is what steers the airplane while taxiing. The pilot controls the nose wheel by a device called a tiller. The nose wheel is much smaller than the main wheels as it doesn’t bear as much weight.
Tires leave their mark on every landing so you may notice quite an accumulation at each end of the runway, about one thousand feet down the runway where airliners touch down. Part of runway maintenance, is to remove the build up of rubber. For Grand Prix drivers laying some rubber is part of their job, but for pilots it’s a challenge to leave as little rubber as possible by smooth landings.


And here's one draft for "just the facts"

Rolling with Facts:
Or (On the Roll) or (The Wheel Facts) or (Wheelie Interesting)

1. Company that supplies Air Canada with tires: Goodyear (Now Michelin)

2. Number of tires Air Canada owns: Only the ones installed on aircraft, others are leased

3. Price for A340 tire: $2100

4. Weight of biggest tire Air Canada has in service (54 inch (137 cm) diameter): 145 Kg

5. Number of tire and wheel shops at Air Canada: Three: Toronto, Montreal and Vancouver

6. Average life span of main landing gear tires: 300 landings

7. Average life span for nose wheel tires: 200 landings

8. Number of tires on airbus 340-500 (Air Canada’s largest): 14

9. Average time to change a tire: About one hour for two people

10. Aircraft tires are filled with this gas: Nitrogen

11. Reason for Nitrogen: Prevent freezing, will not support combustion, deters corrosion

12. Repetitive thumping noise heard while barrelling down the runway: Wheels moving over embedded centerline lights or over joints in concrete

13. Main B767 tire can be re-treaded this amount of times: six

14. Before re-treading this inspection is performed: Holographic technique

15. Number of groves on aircraft tire: four

16. Tires on the RJ Challenger can be re-treaded this many times: zero

17. Other devices found on wheels: Carbon brakes, Anti-skid system, brake temperature sensors

18. This system is found on Air Canada’s new A340-500's: TPIS (Tire Pressure Indicating System)

19. Maximum tire speed for A340-500: 204 knots

20. Weight of A340 wheel assembly (tire/rim): 240 Kg

21. Weight of RJ Challenger wheel assembly: About 40 Kg

22. Can a wheel be changed with passengers on board? Yes

23. Time taken to change an RJ nose wheel: twenty minutes


24. Tire pressure of main wheels RJ Challenger: 169 to 177 P.S.I
Aircraft Operating Manual 2.32.10 page 10

25. Device on wheels to prevent skidding: Antiskid

26. Number of wheels on world’s largest cargo airplane (Russian AN225): Thirty two

27. Number of wheels on the soon to be built world’s largest airliner (Airbus 380): Twenty

28 Number of wheels on Air Canada’s smallest connector aircraft (Beech 1900): Five

29. Type of aircraft jacks at Air Canada: axle jacks and tripod jacks

30. Range of jack lifting capacity: 5 tons to 100 tons

31. Device to aid in removing/replacing aircraft wheels: Wheel Change Dolly

32. How main wheels are stopped from spinning during gear retraction: Automatic wheel braking

33. How nose wheel is stopped from spinning during retraction: Scrubbers
(There is no brake system on nose wheels)

34. System pilots use to determine braking response for wheels on slippery runways:
CRFI (Canadian Runway Friction Index)