Tyres cannot be taken for granted on any aircraft. Proper aircraft tyre inspection can prevent one of major aircraft accident due to tyre failure. Let’s go through some typical tyre inspection procedure.
Aircraft Tyre Inspection
All Aircraft tyres should be visually inspected for:
- Treadwear – Tyres should be removed when the tread has worn to the base of any groove at any spot or up to 1/8 of the tyre circumference.
- Uneven Wear – If the tread wear is excessive on one side then tyre can be demounted and turned around, provided there is no exposed fabric. Gear misalignment can also cause this condition but should be corrected.
- Cuts – Inspect the tread for the cuts and other foreign object damage and mark with crayon or chalk.
- Sidewall Damage – Remove tyre from service if cuts, cracking and snags extend down to the casing ply in the sidewall and bead areas.
- Bulges – Bulges in any part of tyre tread, sidewall or bead area may indicate a separation or damaged tyre. Mark with crayon and remove from service immediately.
Air Injection Inspection
Tubeless tyres may be air injected with dry air or nitrogen to inspect the casing for proper venting, separations, bead and liner condition, etc.
Non Destructive Inspection (NDI)
NDI includes Holography, Shearography, Ultrasonic, and X-ray.
Initial Tyre Inflation
Prior to inflation, ensure the wheel is correctly assembled in accordance with the Wheel Manufacturer’s Maintenance Manual. The initial inflation of a newly fitted wheel assembly should always be carried out within an approved safety cage. Manufacturers recommend the use of Nitrogen or other inert gas (with a maximum of 5% oxygen content) when inflating aircraft tyres.
Inflation Tyre Pressure Checking
It is essential that aircraft tyres be maintained at the correct inflation pressure. Any deviation from specified operational inflation pressures will affect both the performance and safe operation of the tyre.
Under-inflation will increase tyre deflection resulting in excessive heat generation and over-stressing of the carcass leading to either ply or tread separation.
Over-inflation will accelerate wear in the tread crown area and render the tyre more susceptible to foreign object damage (FOD). Therefore it is essential that tyre inflation pressures are checked and adjusted on a regular basis, at least every 24 hours or preferably at each pre-flight inspection.
Tyres on multi-bogie gears can not be visually inspected for equal deflection, because if one tyre is under-inflated then the companion will take the load of both tyres and will, therefore, appear at equal deflection, in any case, visual inspection is totally unsatisfactory and dangerous.
All inflation pressures in rating tables are usually for unloaded tyres ambient temperature (cold). A two hour cooling time should be allowed after landing before checking inflation pressure.
Further Read: Top 10 Tips for Aircraft Tyres Maintenance
Tyre Pressure – Loaded vs Unloaded Condition
Most tyres are put into service at loads less than the rated load. In order to maintain the design operating conditions of the tyre, the operating inflation pressure is adjusted accordingly. This adjustment is in direct proportion to the rated load of pressure.
Many inflation checks are made while the tyre is mounted on the aircraft. Under loaded conditions, the measured pressure of the tyre will be a value 4% greater than the unloaded pressure due to the weight of an aircraft.
Tyre Pressure vs Temperature Relationship
The relationship between tyre temperature and tyre pressure is proportional. As the temperature of the tyre increases, so the pressure will also increase. The inverse is also true. When the tyre temperature is reduced, the pressure will also reduce.
The manufacturer has found that as a general rule, a temperature change of 3°C will result in a tyre pressure change of approximately 1%.
Aircraft Tyre Care Tips For Pilot
Needless tyre damage and excessive wear can be prevented by proper handling of the aircraft during taxi, landing, and takeoff.
The heavy use of aircraft brakes introduces heat into the tyres. So avoid heavy use of aircraft brakes.
Sharp radius turns also increases the heat, tread abrasion and side loads on the tyre. Plan ahead to allow the aircraft to slow without heavy braking and make large radius turns to avoid these conditions.
Most tyre failures occur during takeoff which can be extremely dangerous. Heavy braking during aborted takeoffs is also a common cause of takeoff tyre failure.