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Michelin Aircraft Tire Reliability, Safety &

Performance

AGENDAProof of the need……INFLATION PRESSURE!

– initial inflation– pressure monitoring– pressure effects

Controls for Tire Damage: FOD

Proof of the need: Learjet 60 Crash – CAE?

Proof of the need: Concord?

Learjet 60 @ CAE: Tire Related?

• Tire pieces begin at 2300 feet after takeoff roll.

• Rim scar marks began at 5200 feet thru end of runway.

• All four tires destroyed. Only tire beads remained on wheel remnants

Tire Related?

Causes/Responses:– Preventative?– Reactive?

Let us focus on prevention. Success here prevents a “Reactive” response by the pilots.

Tire Related?

Most common causes for tire failure events:

– Over-deflection (under-inflated)– Foreign Object Damage (FOD)– Fuze plug release (dragging

brake heat)– Stripped ribs due to high lateral

forces (high speed turn-out)

Tire Related?

Most common causes for tire failure events:

– Over-deflection (under-inflated)– Foreign Object Damage (FOD)

– Fuze plug release (dragging brake heat)

– Stripped ribs due to high lateral forces (high speed turn-out)

Tire Related?

The single most important thing to prevent tire related incidents is –

Inflation Pressure!

MaintainingProper Inflation

Why is it important?

Under-Inflation May Cause:• Vibration (bias type)

• Wheel Slippage

• Tire/Wheel damage

• Irregular shoulder wear

• Faster wear rate

• Thrown tread/Tire

failure

Over-Inflation May Cause:• More

susceptibility

to FOD damage

• Increased wear rate

(less contact patch)

• Irregular wear in the

center ribs

Deflection

Definition: The difference between the unloaded and loaded tire section heights

Typical Deflection

Trucks: 12%

Cars: 18%

Aircraft: 32%

Bias/Radial Comparison

Bias Tire• The tread flexes with

the tire:– Contact patch deforms– Contact patch moves– Casing plies tend to Casing plies tend to

scissor in relation to scissor in relation to each other creating each other creating heat.heat.

Radial Tire• Sidewalls and tread function

separately; tread is not affected by sidewall flexing:– Contact patch doesn’t deform– Less movement in the contact

patch– No movement between nylon

plies

Why is inflation pressure Important?

Normal Footprint

Notice the squirm

Severely over-loaded/under inflated

Pressure Effects: Loss vs Temp.

• Rule: Pressure change 1% per each 5

• Example Calculation:+60 112 134

156

Temperature Rise F +40 108 129 151

+20 104 125 145 Operating Pressure 100 120 140

-20 96 115 135

Temperature Drop F -40 92 111 129

-60 88 106 124

Tire Related?

Most common causes for tire failure events:

– Over-deflection (under-inflated)

– Foreign Object Damage (FOD)– Fuze plug release (dragging brake

heat)

– Stripped ribs due to high lateral forces (high speed turn-out)

In Service Removal Criteria• Cuts/FOD damage to tread area:

– Injury severs or extends across a rib– Undercutting at base of any cut– Round objects >3/8” dia.– Reaches carcass/belt plies

In Service Removal CriteriaSidewall Cuts

Tire must be changed whenever cords are

visible.

In Service Removal CriteriaWeather/Ozone Cracking

Looks bad but only

change if cord can be seen under the cracks

SummaryProof of the need……INFLATION PRESSURE!

– initial inflation– pressure monitoring– pressure effects

Controls for Tire Damage: FOD

Safety First• When working on or around aircraft tires,

following established safety procedures is critical

• Aircraft tire and wheel assemblies operate under high pressures in order to carry the loads imposed on them – treat them with the same respect that any other high pressure vessel would be given

For More Information

• Michelin® Aircraft Tire Care & Service Manual and Engineering Data Book– Available on CD or in print

• Certified Tire Expert Programs Levels I & II– Available on CD or in print

• Call us!

Questions?