How much corrosion is too much?

"Carl Orton" wrote in message ...

See some pics below. The first is an inspection cover. The 2nd is the
interior of the tail inspection area. With mirrors, you can see the "piles"
on the lower surface of the horizontal stab skin.

http://f2.pg.photos.yahoo.com/ph/cor...bum?.dir=/4be0

Doesn't look too good in the photos. I'd have a really close look
at the outside surfaces, opposite the corroded areas, and look for
tiny blisters. Poke these with a small, sharp tool like an awl, and if
it goes through easily, the metal is shot. BTDT.
There might be much worse corrosion in the riveted joints where
you can't see so well. Such areas tend to trap moisture, and
electrical current through these areas can accelerate corrosion.
Look for animal nests inside pest-accessible areas like the wings
and elevators (it is a 172, right?). They get in through lightening
holes (inboard ends of elevators and between aileron and wing) and do
terrific damage with their wastes.

Dan

No outside blisters whatsoever (I thought the same thing). Yes, it's a 172.

"Dan Thomas" wrote in message
om...
"Carl Orton" wrote in message
...

See some pics below. The first is an inspection cover. The 2nd is the
interior of the tail inspection area. With mirrors, you can see the
"piles"
on the lower surface of the horizontal stab skin.

http://f2.pg.photos.yahoo.com/ph/cor...bum?.dir=/4be0

Doesn't look too good in the photos. I'd have a really close look
at the outside surfaces, opposite the corroded areas, and look for
tiny blisters. Poke these with a small, sharp tool like an awl, and if
it goes through easily, the metal is shot. BTDT.
There might be much worse corrosion in the riveted joints where
you can't see so well. Such areas tend to trap moisture, and
electrical current through these areas can accelerate corrosion.
Look for animal nests inside pest-accessible areas like the wings
and elevators (it is a 172, right?). They get in through lightening
holes (inboard ends of elevators and between aileron and wing) and do
terrific damage with their wastes.

Dan