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 struts 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 struts 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
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
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
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
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.
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