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.

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.

10. Install the air tiller valve and inflate the strut, as previously described.

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

Figure 12-21.-Landing gear shock strut tools.

nut and reinflating the strut, the strut must be dis-assembled and the packings replaced.

The tools shown in figure 12-21 are typical of the tools used during disassembly and assembly of landing gear shock struts. Normally, each tool is designed for, and should be used only on, one type of installation. When using wrenches, you must take care to maintain the lugs of the wrenches in their respective positions.

Slippage of the wrench, when under torquing conditions, may cause damage to aircraft parts, the tool, or even injury to personnel. NEVER place extension handles of any type on these tools to increase the applied force.

These tools, like other special tools, should be kept where they will not be subjected to rough handling, which could cause mushroomed or deformed surfaces, making them useless for aircraft repair. Shock strut disassembly and replacement of packings is a requirement for advancement to first class; therefore, it is not covered in this training manual.