Aircraft Tires
Care and Maintenance Tire Care and Maintenance
4. Inflation in the Tire Shop
The aircraft tire is designed to be operated at specific "deflection". If the inflation pressure is incorrect, this deflection becomes out of designed range. Such operating condition may cause significant adverse influence on durability, leading to substantial consequences such as quicker tire fatigue, internal separation, and burst.
A. Recommended Inflation procedures
The inflation must be done by using the safety cage.
Nitrogen is recommended for prevention of combustion and reduction of oxidization of the "innerliner".
The tire structure stretches after the inflation for a significant period of time, since the nylon cords are used as reinforcing material. This stretch results in reduction in the inflation pressure. Therefore, readjustment of inflation pressure after stabilizationperiod is mandatory to ensure the correct pressure.
The stabilization period is shown in the Table 1.
The readjustment can be done at PNO (unloaded service pressure) instead of the rated pressure.
Pressure Gauge:
Recommended specifications are error of 0.25% and less, and minimum digit of 2 psi.
Table 1: Period for Stabilization
| Period | Procedure |
|---|---|
| Min. 12 hours* | Normal |
| Min. 2 hours | Alternate |
* : "Min. 12hours" for the stabilization is recommended in AC 20-97B issued by FAA.
Natural pressure loss may occur even after the stabilization. If the loss does not exceed criteria specified in the Table 2 , the tire is normal and serviceable.
Table 2: Air Retention Criteria
| Period | Criteria of pressure loss | Procedure |
|---|---|---|
| 24 hours** | 5 percent | Normal |
| 12 hours | 2.5 percent | Alternate |
** : "Min. 24hours" for the retention test is recommended in AC 20-97B issued by FAA.
In case the pressure loss exceeds the criteria, the following measure shall be taken.
| a) | Confirm change in ambient temperature. If the room becomes cooler, the pressure descends naturally. Pressure goes down 3.7% for room temperature down by 10 deg C. |
|---|---|
| b) | If temperature variation is not the cause, most probable cause is attributed to condition of wheel. Check shall be done as shown below. |
| 1) | To investigate air leak from the wheel. By spraying soap solution, find air bubble on the surface of the wheel and components, such as air valve, thermal fuse. |
|---|---|
| 2) | When the cause is not detected, dismount the wheel, check the wheel elements and readjust. |
| 3) | If the problem persists, the tire should be remounted on a different wheel. If the problem still persists, put the tire aside for investigation by Bridgestone engineers. |
[Emergency inflation procedure]
When time does not allow the above procedure to be applied, the following procedure may be applied for pressure retention check.
The inflated tire is stabilized for minimum 1 hour.
Readjust the pressure at 105% of PNO (unloaded service pressure). Check air leakage by spraying water or soap solution over the tire and entire wheel surface. If there is no air bubble, the assembly can be installed on aircraft.
For 48 hours after the installation, the inflation pressure must be checked before each flight.
"The use of TPIS or TPMS is an acceptable means for checking the inflation pressure during this period for pressure check, if it is in accordance with the airframe manufacturer’s AMM"
If the pressure retention is below 90 percent of the service pressure, the tire should be removed.
Category Link:
Tire Care and Maintenance
- 10. Removal by tire condition other than tread wear
11. Dismounting Bias Tires
12. Dismounting Radial Tires
13. Remounting of tires
14. Tire condition unsuitable for retreading - 15. Matching Tire Diameters
16. Tire Flat-spot
17. Protection from Contamination
18. Maintenance of Airport Surfaces - 19. Tires in Other than Aircraft Service
20. Storage of Tires
21. Handlings of tires
22. Transportation & Storage of Tire/Wheel Assemblies
23. Precautions during Unloading
24. Service Claim Memorandum
