Alternately, it may contain a hole through which a valve  stem extension may pass from the inner wheel half or the  valve stem itself may fit through such a hole if a tube-type  tire is used. An aircraft wheel assembly is inspected while on the aircraft  as often as possible. A more detailed inspection and any  testing or repairs may be accomplished with the wheel  assembly removed from the aircraft. The general condition of the aircraft wheel assemblies can  be inspected while on the aircraft. Any signs of suspected  damage that may require removal of the wheel assembly from  the aircraft should be investigated. The landing gear area is such a hostile environment that  the technician should inspect the landing gear including  the wheels, tires, and brakes whenever possible. Proper  installation of the wheels should not be taken for granted.  All wheel tie bolts and nuts must be in place and secure.  A missing bolt is grounds for removal, and a thorough  inspection of the wheel halves in accordance with the wheel  manufacturer’s procedures must be performed due to the  stresses that may have occurred. The wheel hub dust cap and  anti-skid sensor should also be secure. The inboard wheel  half should interface with the brake rotor with no signs of  chafing or excessive movement. All brake keys on the wheel  must be present and secure.  Examine the wheels for cracks, flaked paint, and any  evidence of overheating. Inspect thermal plugs to ensure  no sign of the fusible alloy having been melted. Thermal plugs that have permitted pressure loss in the tire require  that the wheel assembly be removed for inspection. All other  wheels with brakes and thermal plugs should be inspected  closely while on the aircraft to determine if they too have  overheated. Each wheel should be observed overall to ensure  it is not abnormally tilted. Flanges should not be missing any  pieces, and there should be no areas on the wheel that show  significant impact damage.  Axle nut torque is of extreme importance on an aircraft wheel  installation. If the nut is too loose, the bearing and wheel  assembly may have excessive movement. The bearing cup(s)  could loosen and spin, which could damage the wheel. There  could also be impact damage from the bearing rollers which  leads to bearing failure.  [Figure 13-62]  An over-torqued axle  nut prevents the bearing from properly accepting the weight  load of the aircraft. The bearing spins without sufficient  NOTE: As a precautionary measure, remove only one tire  and wheel assembly from a pair at a time. This leaves a tire  and wheel assembly in place should the aircraft fall off its  jack, resulting in less chance of damage to the aircraft and  injury to personnel.  13-37 Caution: Deflate the tire before starting the procedure of  removing the wheel assembly from the aircraft. Wheel  assemblies have been known to explode while removing the  axle nut, especially when dealing with high pressure, high  performance tires. The torque of the nut can be the only  force holding together a defective wheel or one with broken  tie bolts. When loosened, the high internal pressure of the  tire can create a catastrophic failure that could be lethal to  the technician. It is also important to let aircraft tires cool  before removal. Three hours or more is needed for cool  down. Approach the wheel assembly from the front or rear,  not broadside. Do not stand in the path of the released air  and valve core trajectory when removing air from the tire  as it could seriously injure the technician should it release  from the valve stem. Discrepancies found while inspecting a wheel mounted on  the aircraft may require  further inspection with the wheel  removed from the aircraft. Other items such as bearing  condition, can only be performed with the wheel assembly  removed. A complete inspecti on of the wheel requires that the  tire be removed from the wheel rim. Observe the following  caution when removing a wheel assembly from an aircraft.  lubrication to absorb the heat  caused by the higher friction  level. This too leads to bearing failure. All aircraft axle nuts  must be installed and torqued  in accordance with the airframe  manufacturer’s maintenance procedures. Figure 13-62.  Improper loose torque on the axle nut can cause  excessive end play leading to bearing race damage known as  scalloping. Eventually, this leads to bearing failure. Off Aircraft Wheel Inspection  Wheel Inspection On Aircraft Inspection Proper Installation Axle Nut Torque Scalloping