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.
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.
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.
particular attention to the following:
that the bead seating area of the wheel is clean
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.
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.
grooves in the wheel halves should be checked for damage or other
debris that would prevent the O-Ring from properly seating.
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.
the inspection of a used O-Ring for its integrity not be practical or
manageable, replace with anew O-Ring with each tire change.
Before mounting any tire, verify that
the tire is correct for the intended application. Use the following checklist:
that the tire markings are correct for the
required application (size, ply rating, speed rating, part number, TSO
inspect the outside of the tire for:
caused by improper shipping or handling of the tire.
tears or other foreign objects penetrating the rubber.
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.
distortions. Cracking that reaches cords.
from foreign substances (oil, grease, brake fluid, etc.), which can
cause surface damage (blisters or swelling).
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.
of Inner Tubes
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.
Michelin radial tires are of tubeless design. Never use an inner tube or
mount on a tube‑type wheel.
of Tire Beads
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.
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, use of a mounting lubricant is not specified, unless
approved by the airframer.
be sure that the wheel, tire, and assembly
components are in good condition and free of debris.
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.
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.
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 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.
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.
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
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
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.
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
Special Procedure To Properly Seat Tube-Type Tires
To seat tire beads properly on the wheel:
the tire to the recommended pressure for the aircraft on which it is to be
completely deflate the tire.
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
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.
With tubeless tires, this inflation-deflation-reinflation procedure is not
PRESSURE RETENTION CHECK
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%.
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
If the pressure loss is within the
acceptable 5% limit, the assembly is now ready to be installed on the
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.
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
Electronic pressure measuring equipment
with ± 0.007 bars / 0.1 psi sensitivity is recommended for this test method.
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.
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
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
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.
not expose the tire to excessively high temperatures (greater than 400
not expose the tire to direct sunlight or to high ozone concentrations.
contact with contaminants (oil, grease, etc.).
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
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
Reinflate to operating pressure
before mounting on the aircraft.