One is conducted with the tire mounted on the wheel. The other inspection is conducted with the tire dismounted. Tires must also be inspected before each flight for obvious damage that may have been caused during or after the previous flight. Maintaining the correct inflation pressure in an aircraft tire is essential to safety and to obtain its maximum service life. Military aircraft inner tubes and tubeless tire liners are made of natural rubber to satisfy extreme low-temperature performance requirements.
Natural rubber is a relatively poor air retainer.
This accounts for the daily inflation pressure loss and the need for frequent pressure checks. If this check discloses more than a normal loss of pressure, you should check the valve core for leakage by Figure 11-16. Tire slippage mark. Replace the valve core if it is leaking. After making a pressure check, you should always replace the valve cap.