Insufficient fluid, or air in the strut, cause the compression
stroke to not be properly limited. The strut could bottom
out, resulting in impact forces to be transferred directly to
the airframe through the metallic structure of the strut. In
a properly serviced strut, the extension stroke of the shock
strut operation occurs at the end of the compression stroke.
Energy stored in the compressed air in the upper cylinder
causes the aircraft to start moving upward in relation to the
ground and lower strut cylinder as the strut tries to rebound
to its normal position. Fluid is forced back down into the
lower cylinder through restrictions and snubbing orifices. The
snubbing of fluid flow during the extension stroke dampens
the strut rebound and reduces oscillation caused by the spring
action of the compressed air. A sleeve, spacer, or bumper
ring incorporated into the strut limits the extension stroke.