struts. The amount a strut is inflated depends upon the specific aircraft strut being serviced. One manufacturer may use a strut inflation chart, such as the one shown in view D of figure 12-19. The strut is measured as indicated at dimension “A.” This measurement, in inches, is then located on the bottom of the inflation chart. For example, locate the measurement of 1.75 inches on the chart. From this point, vertically trace an imaginary line until it intersects the curved line. At this point of intersection, horizontally trace a second imaginary line to the left edge of the chart. The figure indicated at this point (550 psi) is the required pressure for that particular extension of the strut. All aircraft struts are not measured from the same points. View E of figure 12-19 shows another location where strut extension is measured. The proper procedure to use will always be found on the instruction plate attached to the shock strut. If these instructions are not legible, consult the applicable MIM. If the strut’s chamber is underpressurized, the strut may not overcome normal O-ring friction during extension on takeoff. This condition could prevent the strut from fully extending, thus the torque scissors limit switch would not actuate to close the electrical circuit to retract the gear. It would also cause the strut to bottom during taxiing and landing operations. If the strut’s chamber is overpressurized, the additional pressure will tend to keep the strut pressurized after takeoff. On those aircraft that use shrink mechanisms, the shrink mechanisms may be overloaded or stall the strut actuator as the gear retracts. If the gear retracts in the wing without shrinking, due to the failure of the shrink mechanism, damage to both the wing and landing gear may result. 10. Tighten the air valve swivel hex nut to a recommended torque of 50-70 inch-pounds. 11. Remove the high-pressure air-line chuck and install the valve cap fingertight Because some aircraft struts require special servicing procedures, the General Information and Servicing section of the applicable MIM should always be checked before servicing the shock struts of any aircraft. Bleeding If the fluid level of a shock strut has become extremely low or, if for any other reason, air is trapped in the strut cylinder, it may be necessary to bleed the strut during the servicing operation. Bleeding is performed with the aircraft placed on jacks. In this position, the shock struts can be extended and compressed during the filling operation, expelling all of the entrapped air. As mentioned earlier, certain aircraft must be placed on jacks for routine servicing of the shock struts. The following is a typical bleeding procedure. 1. Construct a bleed hose that contains a fitting suitable for making an airtight connection to the shock strut filler opening. The hose should be long enough to reach from the shock strut tiller opening to the deck when the aircraft is on jacks. 2. Jack the entire aircraft until all shock struts are fully extended. 3. Release the air or nitrogen pressure in the strut to be bled, as previously described in this chapter. 4. Remove the air tiller valve assembly. 5. Fill the strut to the level of the filler port with hydraulic fluid. 6. Attach the bleed hose to the filler port, and insert the opposite end of the hose into a quantity of clean hydraulic fluid. 7. Place an exerciser jack or other suitable single-base jack under the shock strut jacking point. See view C of figure 12-19. Compress and extend the strut fully (by raising and lowering the jack) until the flow of air bubbles from the strut has completely stopped. NOTE: Compress the strut slowly and allow it to extend by its own weight. 8. Remove the exerciser jack, and then lower and remove all other jacks. 9. Remove (he bleed hose from the shock strut. 10. Install the air tiller valve and inflate the strut, as previously described. Inspection Shock struts should be inspected regularly for leakage of fluid and for proper extension. Exposed portions of the strut pistons should be cleaned in the same manner as actuating cylinder pistons during preflight and postflight inspections. Exposed pistons should be inspected closely for scoring and corrosion. Excessive leakage of fluid can usually be stopped by deflating the strut and tightening the packing gland nut. If leakage still persists after tightening the packing gland 12-25