GENERAL

Proper mounting procedures simplify the job of servicing aircraft tires, while at the same time increasing safety and reducing the chances of damaging tires or wheels. Do not mount aircraft tires without the proper equipment, instructions, and operator training.

Virtually all modern aircraft wheels are of two types: split wheel type, i.e., two "halves" joined by removable tie bolts, or the removable flange type. Both designs facilitate the mounting (and dismounting) of the tire. Show careful attention in handling, assembling and disassembling wheel components to avoid damage to critical surfaces.

PREMOUNTING CHECKLIST

Wheels

Careful attention to details is necessary to successfully mount aircraft tires for trouble free service. Make sure you are thoroughly familiar with and inspect all key wheel parts before beginning to mount a tire.

To assist in this process, wheel manufacturers publish specific instructions in their maintenance and overhaul manuals. Follow their recommendations and procedures for wheel assembly and disassembly to obtain trouble-free mounting and dismounting.

Direct particular attention to the following:

  • Ensure that the bead seating area of the wheel is clean and uncontaminated.
  • Mating surfaces of the wheel halves should be free of nicks, burrs, small dents, or other damage that could prevent the surfaces from properly mating or sealing. Painted or coated surfaces should be in good condition; not badly chafed, chipped, etc.
  • Be sure fuse plugs, inflation valves and wheel plugs are in good condition, properly sealed against loss of pressure and correctly torqued per the manufacturer's instructions.
  • O-Ring grooves in the wheel halves should be checked for damage or other debris that would prevent the O-Ring from properly seating.
  • O-Rings themselves must be of the proper material, as specified by the wheel manufacturer, for the intended application and temperature conditions. Inspect O-Rings for cracking, cuts, or other damage. Particular attention should be given to permanent deformations in the O-Ring. O-Rings found with deformations should be replaced. Proper sealing of the wheel halves is critical in providing trouble-free service.
  • Should the inspection of a used O-Ring for its integrity not be practical or manageable, replace with anew O-Ring with each tire change.

Tires

Before mounting any tire, verify that the tire is correct for the intended application. Use the following checklist:

  • Check that the tire markings are correct for the required application (size, ply rating, speed rating, part number, TSO marking).
  • Visually inspect the outside of the tire for:
    • Damage caused by improper shipping or handling of the tire.
    • Cuts, tears or other foreign objects penetrating the rubber.
    • Permanent deformations.
    • Debris or cuts on the bead seating surfaces. Clean the tire bead surfaces with either a clean shop towel, a soap/ water solution, or with denatured alcohol as may be necessary.
    • Bead distortions. Cracking that reaches cords.
    • Contamination from foreign substances (oil, grease, brake fluid, etc.), which can cause surface damage (blisters or swelling).
  • Inspect the inside of the tire to be sure there is no foreign material present. Be sure that the inner liner condition is good, that is, without wrinkles. Check for liner damage caused by improper shipping or handling of the tire.

Refer to the section on "Tire Serviceability Criteria" for damages. If in question, tires should not be used and should be returned to a certified repair or retread station for further inspection and disposition.

MOUNTING

Use of Inner Tubes

  • Bias Tires
    • All Michelin bias or cross ply tires, whether tube type or tubeless, are suitable for operation with tubes approved for the particular tire size and application on tube type wheels.
  • Radial Tires
    • All Michelin radial tires are of tubeless design. Never use an inner tube or mount on a tube‑type wheel.

Lubrication of Tire Beads

  • Bias Tires
    • Because of their typically wide bead flat, when installing bias tires on aluminum wheels, lubricate the toes of the beads with an approved 10 % vegetable oil soap solution.

Do not use lubricant with magnesium alloy wheels! Lubricants manufactured from a petroleum base are not recommended as hydrocarbons have a known detrimental effect on rubber pounds.

  • Radial Tires
    • For radial tires, use of a mounting lubricant is not specified, unless approved by the airframer.

Tire/Wheel Assembly

  • Again, be sure that the wheel, tire, and assembly components are in good condition and free of debris.
  • Lubricate the O-Ring (as specified by the wheel manufacturer) and install in the wheel groove or channel. Be sure the O-Ring is free of kinks or twists.
  • Position the previously inspected tire in front of the first wheel half. If a bias tire, lubricate the beads as required. Slide the tire on the wheel.
  • When mounting tube-type tires, dust the tube and the inside of the tire with tire talc or soapstone before installing the tube. This will prevent the tube from sticking to the inside of the tire or to the tire beads. Dusting also helps the tube assume its normal shape inside the tire during inflation, and lessens the chances of wrinkling or thinning from irregular stretching. (Caution: Use care not to damage tube when mounting.)

To be consistent with the practice of mounting the tire serial number to the outboard wheel half, tubes should be installed in the tire with the valve projecting on the serial numbered side of the tire.

  • Assemble the two wheel halves, being sure to align the light point of each half 180' apart to insure the optimum balance of the assembly. When aligning the wheel halves, be careful not to damage the O-Ring in the wheel base, which seals the wheel halves.
  • Tire/Wheel Alignment for Balance. The "red" balance mark indicates the light point of the tire's balance. Align this mark with the heavy point of the wheel. Many wheel manufacturers today identify either the light spot or heavy spot of the wheel with markings in the flange area. Follow their instructions on assembly and balance. Be sure to align the tire's light spot 1800 from the wheel's light spot or directly in line with the wheel's heavy spot. In the absence of specific wheel markings, align the tire's red balance mark with the wheel inflation valve. Some aircraft tubes feature balance marks to indicate the heavy portion of the tube. These marks are approximately 1/2" wide and 2" long. When inserting the tube in the tire, its balance mark should be aligned with the balance mark on the tire. If the tube has no balance mark, align the valve with the balance mark on the tire. A properly balanced tire/wheel assembly improves the tire's overall wear characteristics. In addition to severe vibration, an unbalanced assembly will cause irregular and localized tread wear patterns that can reduce the overall performance life of the tire.
  • Be sure that nuts, washers, and bolts are installed in proper order and that the bearing surfaces of these parts are properly lubricated as required. Tighten to manufacturer's recommended torque values.
  • After the tire is mounted on the wheel, the assembly should be placed in a safety cage for inflation with nitrogen. It is recommended that the cage be placed against an outside wall that is strong enough to withstand the effects of an explosion of either the tire, tube or wheel.

The inflation pressure source should be located 10 meters/ 30 feet away from the safety cage with a valve, regulator and pressure gauge installed at that point. The inflation line should then be run to the

safety cage and attached to the wheel valve. This arrangement allows the tire service person to inflate the tire safely using the remote valve.

WARNING! Aircraft tires can be operated up to or at rated inflation pressure, extremely high inflation pressures may cause the aircraft wheel or tire to explode or burst, which may result in serious or fatal bodily injury. Aircraft tires must always be inflated with a properly regulated inflation canister. The high-pressure side should never be used. The safety practices for mounting and dismounting aircraft tires detailed in this Manual must be followed.

Inflating With Nitrogen

Many regulatory agencies require the use of nitrogen when inflating tires for aircraft above a specified Maximum Takeoff Weight (MTOW). Michelin recommends the use of nitrogen when inflating all aircraft tires. Nitrogen provides a stable, inert inflation gas while eliminating the introduction of moisture into the tire cavity.

Aircraft operating procedures for initial inflation and adjustments must comply with applicable instructions as given in FAR 25 or JAR 25.

Oxygen concentration should never exceed 5%.

Special Procedure To Properly Seat Tube-Type Tires

To seat tire beads properly on the wheel:

  • Inflate the tire to the recommended pressure for the aircraft on which it is to be mounted.
  • Next, completely deflate the tire.
  • Finally, reinflate it to the correct pressure (do not fasten the valve to the rim until this has been done). Use a valve extension for inflation purposes if necessary.

This procedure helps remove any wrinkles in the tube and helps prevent pinching the tube under the toe of the bead. It eliminates the possibility of one section of the tube stretching more than the rest and thinning out in that area. Further, it assists in the removal of air that might be trapped between the inner tube and the tire.

Note: With tubeless tires, this inflation-deflation-reinflation procedure is not necessary.

BASIC PRESSURE RETENTION CHECK

Allow for Tire Growth

Newly mounted tire/wheel assemblies should stand for 12 hours to allow for normal tire growth (cord body stretching) and to verify that the assembly is without leaks. After 12 hours, inspect the assembly carefully. Check the tire pressure drop. A 10% drop during tire growth is considered normal. More than that may indicate a leakage problem. Be sure that the tire assembly has remained at a constant ambient temperature (t 3'C/5'F). A drop of 3'C/5'F will reduce inflation pressure 1%.

Check for Leakage

After the growth period, reinflate the tire to the specified operating pressure. Recheck the pressure after a 24-hour period. A pressure loss of 5% or less is considered normal. Be sure that the ambient temperature of the tire has not changed by more than 30C/5'E If a greater than 5% pressure loss occurs, investigate the tire/wheel assembly for leaks. Do not put the tire into service until the leak source is identified and corrected.

If the pressure loss is within the acceptable 5% limit, the assembly is now ready to be installed on the aircraft.

Note that once in service, the tire/wheel assembly maximum daily (24 hours) pressure loss is 5%. Typical rates are 0.2-2.0% per 24-hour period.

ALTERNATE PRESSURE RETENTION CHECK

The above procedure is designed to properly identify pressure retention of tire/ wheel assemblies prior to releasing them for use on aircraft. An alternate, shorter, procedure can be used for tires that have been previously stretched (for example, retreaded tires).

Electronic pressure measuring equipment with 0.007 bars / 0.1 psi sensitivity is recommended for this test method.

Procedure

Allow the newly mounted and inflated assembly to stand for 6 hours in a constant ambient temperature. Check the contained pressure. A gauge pressure drop of <11.25% indicates an acceptable tire/wheel assembly. A gauge pressure drop ~1.25% may indicate a leakage problem and the assembly must be reinflated and the extended, 24-hour leakage check employed.

SIDEWALL VENTING

Aircraft tires are designed to permit any air or nitrogen trapped in the cord body or that diffuses through the liner or tube to escape through special sidewall vents. This venting prevents pressure build-up within the carcass body which might cause tread, sidewall, or ply separations.

Vent holes are placed in the lower sidewall of a tire. The location of each vent hole on the new tire is indicated by a colored paint dot. Simply apply a soap solution to these vent markings. The appearance of small bubbles will indicate diffusion. This bubbling is normal and may be seen at any time while the tire is inflated. Maximum allowable diffusion is 5% for any 24-hour period. Pressure losses in excess of 5% may indicate leakage from other sources. In that case, the tire and wheel assembly should be carefully tested for leaks, preferably by total immersion, before placing it into service. If no assembly leaks are found, dismount and have the tire inspected by the manufacturer or a qualified repair shop.

Note: Do not identify a tire as a leaker solely on the rate of bubbles from these vent holes. This judgment should be based on pressure loss as measured with a calibrated gauge, preferably the same gauge used to initially inflate the tire.

STORAGE OF AN INFLATED TIRE AND WHEEL ASSEMBLY

Once a tire has been properly mounted and the assembly verified for pressure retention, only minimal precautions need be taken.

  • Do not expose the tire to excessively high temperatures (greater than 400 C/1040 F).
  • Do not expose the tire to direct sunlight or to high ozone concentrations.
  • Avoid contact with contaminants (oil, grease, etc.).
  • Tires to be stored for long periods of time should have their inflation pressure reduced to 1/4 (25%) of normal operating pressure or 40 psi, whichever is the lesser.
  • Serviceable tire assemblies being transported, particularly as cargo in aircraft, should have their inflation pressures reduced to 25% of operating pressure or 3 bars/Approx 40 psi, whichever is the lesser. Thus, a tire with 180 psi operating pressure should be transported with an inflation pressure of 44 psi or less. Maintain sufficient pressure to keep tire beads seated. Unserviceable tire assemblies should be transported uninflated (0 psi/O bars).

Reinflate to operating pressure before mounting on the aircraft.

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