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On Jul 4, 4:56 pm, "Mike" wrote:

Obviously, you haven't seen some of the things I have seen. One of
the
more tender, and more invisible spots on some airframes is where the
horizontal stabilizer connects to the fuze. Many designs allow a
tremendous moment arm for any non-balanced load on the stabilizer to
stress the attachment points. This shows up as cracked spars on
Cessnas,
and I have seen stressed and cracked fittings from another airframe.
How
can this happen? Well on Cessnas it happens from folks using improper
procedures to back the plane into a parking spot. It can also happen
from
innocent (but ignorant) bystanders, mowers, animal activity, or any of
thousands of other posibilities.

I always give each side a good heave up and down for this very reason, so
such can easily be checked on the preflight for impending failure.

A good heave up and down on the end of the stab of a 172
flexes the center of the forward spar, eventually cracking it. A
gentle bit of push-pull is all that's needed, to see if there's
unusual tip travel. I bet your spar is cracked now. Many are. Cessna
calls for stopdrilling the crack unless it has reached the spar
flange, in which case it has to be repaired. I once flew a 172 that I
subsequently found had a broken spar, busted clear through both
flanges so that the skin was all that was holding it. The thing could
have killed me if I gotten into turbulence or had to take violent
evasive action. We run several 172s and have seen cracks, up to four
of them, in a spar; we now forbid students to push down on the things.
No more cracks.
172s suffer cracking at the bottom of the aft doorposts. Some
models crack inside the forward doorposts. Do I need to point out that
these doorposts are what the wing pulls on to lift the airplane, along
with the struts? No preflight will find those. The wing spar attach
lugs are known to crack at the bolt holes. In older 172s the forward
elevator bellcrack bracket would break loose, reducing elevator
control. In newer 172s (rod-style gear; 1973 or so and on) the landing
gear retaining bolt sometimes shears and totals the airplane on
landing. As the years go by, these older airplanes will become the
subjects of ADs addressing age-related airframe failure, probably
after a couple come apart in flight. Sooner or later.

1. By "good heave" I don't mean raising the nosewheel off the ground. I
just mean applying enough pressure both directions to listen for any
irregularities.

2. I don't have a 172.