Cessna Wing Skins

[Tom Cummings]

My Cessna 172 M (1973) is being annualed. The top wing skin panels above the
wing tanks (Standard tanks) have to come off to inspect the area for
corrosion. We got all the screws removed. According to the service manual,
that is all that is supposed to be securing the panel. (Dozens of screws
around the perimeter of the skin and six screws around the fuel filler neck
is all that is stated to be removed). The skins would not remove after
careful tugging and pulling. (the fuel cap was removed for this).Then I
finally found three rivit type fasteners also around the filler neck. They
apparently hold the skin in place in addition to the six screws but there is
not any reference in the manual about removing them or drilling the heads of
the rivits off. If they are indeed rivits, they are flush head type because
they are smooth with the skin's surface. The heads are about 1/8th inch in
diameter. I was hoping they could be merely some alignment pins. I removed
the small inspection cover over the fuel transmitter (sender) to get a
better grip on the panel near the filler neck. When trying to gently lift
the skin panel upward, it is obvious that the three rivits are attached to
the panel and to a flange underneath the panel that apparently secures the
filler neck. The panel would not pop clear of them. So I don't think they
are alignment pins.
Anyone familiar with this to advise drilling these three fasterners to free
the panel?
Thanks,
Tom Cummings

[Jack Brown]

And you're doing this why? Was corroision seen when you looked though
the (removeable) inspection plates? Has the tank been leaking? In 16
years of owner assisted annuals we've never had to pull skins up like
this.

jb


On Sat, 23 Apr 2005 17:30:59 GMT, "Tom Cummings" >
wrote:

>My Cessna 172 M (1973) is being annualed. The top wing skin panels above the
>wing tanks (Standard tanks) have to come off to inspect the area for
>corrosion. We got all the screws removed. According to the service manual,
>that is all that is supposed to be securing the panel. (Dozens of screws
>around the perimeter of the skin and six screws around the fuel filler neck
>is all that is stated to be removed). The skins would not remove after
>careful tugging and pulling. (the fuel cap was removed for this).Then I
>finally found three rivit type fasteners also around the filler neck. They
>apparently hold the skin in place in addition to the six screws but there is
>not any reference in the manual about removing them or drilling the heads of
>the rivits off. If they are indeed rivits, they are flush head type because
>they are smooth with the skin's surface. The heads are about 1/8th inch in
>diameter. I was hoping they could be merely some alignment pins. I removed
>the small inspection cover over the fuel transmitter (sender) to get a
>better grip on the panel near the filler neck. When trying to gently lift
>the skin panel upward, it is obvious that the three rivits are attached to
>the panel and to a flange underneath the panel that apparently secures the
>filler neck. The panel would not pop clear of them. So I don't think they
>are alignment pins.
>Anyone familiar with this to advise drilling these three fasterners to free
>the panel?
>Thanks,
>Tom Cummings
>
>

[Jon A.]

On Sat, 23 Apr 2005 21:46:31 GMT, (Jack
Brown) wrote:

>And you're doing this why? Was corroision seen when you looked though
>the (removeable) inspection plates? Has the tank been leaking? In 16
>years of owner assisted annuals we've never had to pull skins up like
>this.
>
>jb

Well, I guess he's the third person who doesn't know the answer to the
poster's question!

>
>
>On Sat, 23 Apr 2005 17:30:59 GMT, "Tom Cummings" >
>wrote:
>
>>My Cessna 172 M (1973) is being annualed. The top wing skin panels above the
>>wing tanks (Standard tanks) have to come off to inspect the area for
>>corrosion. We got all the screws removed. According to the service manual,
>>that is all that is supposed to be securing the panel. (Dozens of screws

[Michelle P]

Tom,
Use air tools and go slow.
Electric will create sparks and air tools will not.
Go slow to reduce heat build up.
Michelle (A&P)

Tom Cummings wrote:

>My Cessna 172 M (1973) is being annualed. The top wing skin panels above the
>wing tanks (Standard tanks) have to come off to inspect the area for
>corrosion. We got all the screws removed. According to the service manual,
>that is all that is supposed to be securing the panel. (Dozens of screws
>around the perimeter of the skin and six screws around the fuel filler neck
>is all that is stated to be removed). The skins would not remove after
>careful tugging and pulling. (the fuel cap was removed for this).Then I
>finally found three rivit type fasteners also around the filler neck. They
>apparently hold the skin in place in addition to the six screws but there is
>not any reference in the manual about removing them or drilling the heads of
>the rivits off. If they are indeed rivits, they are flush head type because
>they are smooth with the skin's surface. The heads are about 1/8th inch in
>diameter. I was hoping they could be merely some alignment pins. I removed
>the small inspection cover over the fuel transmitter (sender) to get a
>better grip on the panel near the filler neck. When trying to gently lift
>the skin panel upward, it is obvious that the three rivits are attached to
>the panel and to a flange underneath the panel that apparently secures the
>filler neck. The panel would not pop clear of them. So I don't think they
>are alignment pins.
>Anyone familiar with this to advise drilling these three fasterners to free
>the panel?
>Thanks,
>Tom Cummings
>
>
>
>

[tony roberts]

Did you find corrosion? I'm not aware of any AD that requires removal of
the skins.
I would have thought that you A & E would be doing this if it was
necessary. - and would know how to do it.
Here is Canada, if my understanding is correct, you would be allowed to
remove the skins, but not allowed to reinstall them.
Sorry I'm unable to answer your question but I have one of my own.
Is there an AD? If so, maybe I'm going to have to do the same thing in
my 172H.

Tony

--

Tony Roberts
PP-ASEL
VFR OTT
Night
Cessna 172H C-GICE


In article . net>,
"Tom Cummings" > wrote:

> My Cessna 172 M (1973) is being annualed. The top wing skin panels above the
> wing tanks (Standard tanks) have to come off to inspect the area for
> corrosion. We got all the screws removed. According to the service manual,
> that is all that is supposed to be securing the panel. (Dozens of screws
> around the perimeter of the skin and six screws around the fuel filler neck
> is all that is stated to be removed). The skins would not remove after
> careful tugging and pulling. (the fuel cap was removed for this).Then I
> finally found three rivit type fasteners also around the filler neck. They
> apparently hold the skin in place in addition to the six screws but there is
> not any reference in the manual about removing them or drilling the heads of
> the rivits off. If they are indeed rivits, they are flush head type because
> they are smooth with the skin's surface. The heads are about 1/8th inch in
> diameter. I was hoping they could be merely some alignment pins. I removed
> the small inspection cover over the fuel transmitter (sender) to get a
> better grip on the panel near the filler neck. When trying to gently lift
> the skin panel upward, it is obvious that the three rivits are attached to
> the panel and to a flange underneath the panel that apparently secures the
> filler neck. The panel would not pop clear of them. So I don't think they
> are alignment pins.
> Anyone familiar with this to advise drilling these three fasterners to free
> the panel?
> Thanks,
> Tom Cummings

[Jon A.]

Up to 5!

On Sun, 24 Apr 2005 05:47:16 GMT, tony roberts >
wrote:

>Did you find corrosion? I'm not aware of any AD that requires removal of
>the skins.
>I would have thought that you A & E would be doing this if it was
>necessary. - and would know how to do it.
>Here is Canada, if my understanding is correct, you would be allowed to
>remove the skins, but not allowed to reinstall them.
>Sorry I'm unable to answer your question but I have one of my own.
>Is there an AD? If so, maybe I'm going to have to do the same thing in
>my 172H.
>
>Tony

[Tom Cummings]

The I.A. doing the annual said it is to be pulled and said he has seen
corrosion in planes like this before in this area. No fuel tank leaks. No
corrosion was seen through any of the inspection panels in the rest of the
aircraft. This large top skin panel is the only inspection panel in the fuel
tank area.
Tom
"Jack Brown" > wrote in message
.. .
> And you're doing this why? Was corroision seen when you looked though
> the (removeable) inspection plates? Has the tank been leaking? In 16
> years of owner assisted annuals we've never had to pull skins up like
> this.
>
> jb
>
>
> On Sat, 23 Apr 2005 17:30:59 GMT, "Tom Cummings" >
> wrote:
>
>>My Cessna 172 M (1973) is being annualed. The top wing skin panels above
>>the
>>wing tanks (Standard tanks) have to come off to inspect the area for
>>corrosion. We got all the screws removed. According to the service manual,
>>that is all that is supposed to be securing the panel. (Dozens of screws
>>around the perimeter of the skin and six screws around the fuel filler
>>neck
>>is all that is stated to be removed). The skins would not remove after
>>careful tugging and pulling. (the fuel cap was removed for this).Then I
>>finally found three rivit type fasteners also around the filler neck. They
>>apparently hold the skin in place in addition to the six screws but there
>>is
>>not any reference in the manual about removing them or drilling the heads
>>of
>>the rivits off. If they are indeed rivits, they are flush head type
>>because
>>they are smooth with the skin's surface. The heads are about 1/8th inch in
>>diameter. I was hoping they could be merely some alignment pins. I removed
>>the small inspection cover over the fuel transmitter (sender) to get a
>>better grip on the panel near the filler neck. When trying to gently lift
>>the skin panel upward, it is obvious that the three rivits are attached to
>>the panel and to a flange underneath the panel that apparently secures the
>>filler neck. The panel would not pop clear of them. So I don't think they
>>are alignment pins.
>>Anyone familiar with this to advise drilling these three fasterners to
>>free
>>the panel?
>>Thanks,
>>Tom Cummings
>>
>>
>

[Tom Cummings]

I didnot find any corrosion. There is no A.D. for this. I just think the
I.A. is being thorough. I didn't mean to cause a false alarm.
The A.I. is not aware of the three little rivits or he would have pointed
them out to me. He is out of town this weekend and I thought I 'd check with
this group before he gets back on Monday.
Tom
"tony roberts" > wrote in message
news:nospam-01806A.22502923042005@shawnews...
> Did you find corrosion? I'm not aware of any AD that requires removal of
> the skins.
> I would have thought that you A & E would be doing this if it was
> necessary. - and would know how to do it.
> Here is Canada, if my understanding is correct, you would be allowed to
> remove the skins, but not allowed to reinstall them.
> Sorry I'm unable to answer your question but I have one of my own.
> Is there an AD? If so, maybe I'm going to have to do the same thing in
> my 172H.
>
> Tony
>
> --
>
> Tony Roberts
> PP-ASEL
> VFR OTT
> Night
> Cessna 172H C-GICE
>
>
> In article . net>,
> "Tom Cummings" > wrote:
>
>> My Cessna 172 M (1973) is being annualed. The top wing skin panels above
>> the
>> wing tanks (Standard tanks) have to come off to inspect the area for
>> corrosion. We got all the screws removed. According to the service
>> manual,
>> that is all that is supposed to be securing the panel. (Dozens of screws
>> around the perimeter of the skin and six screws around the fuel filler
>> neck
>> is all that is stated to be removed). The skins would not remove after
>> careful tugging and pulling. (the fuel cap was removed for this).Then I
>> finally found three rivit type fasteners also around the filler neck.
>> They
>> apparently hold the skin in place in addition to the six screws but there
>> is
>> not any reference in the manual about removing them or drilling the heads
>> of
>> the rivits off. If they are indeed rivits, they are flush head type
>> because
>> they are smooth with the skin's surface. The heads are about 1/8th inch
>> in
>> diameter. I was hoping they could be merely some alignment pins. I
>> removed
>> the small inspection cover over the fuel transmitter (sender) to get a
>> better grip on the panel near the filler neck. When trying to gently lift
>> the skin panel upward, it is obvious that the three rivits are attached
>> to
>> the panel and to a flange underneath the panel that apparently secures
>> the
>> filler neck. The panel would not pop clear of them. So I don't think they
>> are alignment pins.
>> Anyone familiar with this to advise drilling these three fasterners to
>> free
>> the panel?
>> Thanks,
>> Tom Cummings

[[email protected]]

On 24-Apr-2005, "Tom Cummings" > wrote:

> I did not find any corrosion. There is no A.D. for this. I just think the
> I.A. is being thorough. I didn't mean to cause a false alarm.
> The A.I. is not aware of the three little rivits or he would have pointed
> them out to me. He is out of town this weekend and I thought I 'd check
> with this group before he gets back on Monday.
> Tom


I suspect the A.I. may not be familiar with 172s, although this is kind of
hard to imagine -- sort of like an auto mechanic not being familiar with
Fords or Chevys.

Anyway, I will have to join the chorus of the bewildered. I co-owned a 172M
for many years and went through maybe 10 owner-assisted annuals. We never
once removed any wing skins. Our A.I. was super thorough, and he taught A&P
at a local technical school. Our plane was always stored outside in the
damp Pacific Northwest, so it's not like our chances for corrosion issues
were below average.

-Elliott Drucker

[tony roberts]

Thanks for clarifying that Tom
You had me worried :)

Tony

In article . net>,
"Tom Cummings" > wrote:

> I didnot find any corrosion. There is no A.D. for this. I just think the
> I.A. is being thorough. I didn't mean to cause a false alarm.
> The A.I. is not aware of the three little rivits or he would have pointed
> them out to me. He is out of town this weekend and I thought I 'd check with
> this group before he gets back on Monday.
> Tom
> "tony roberts" > wrote in message
> news:nospam-01806A.22502923042005@shawnews...
> > Did you find corrosion? I'm not aware of any AD that requires removal of
> > the skins.
> > I would have thought that you A & E would be doing this if it was
> > necessary. - and would know how to do it.
> > Here is Canada, if my understanding is correct, you would be allowed to
> > remove the skins, but not allowed to reinstall them.
> > Sorry I'm unable to answer your question but I have one of my own.
> > Is there an AD? If so, maybe I'm going to have to do the same thing in
> > my 172H.
> >
> > Tony
> >
> > --
> >
> > Tony Roberts
> > PP-ASEL
> > VFR OTT
> > Night
> > Cessna 172H C-GICE
> >
> >
> > In article . net>,
> > "Tom Cummings" > wrote:
> >
> >> My Cessna 172 M (1973) is being annualed. The top wing skin panels above
> >> the
> >> wing tanks (Standard tanks) have to come off to inspect the area for
> >> corrosion. We got all the screws removed. According to the service
> >> manual,
> >> that is all that is supposed to be securing the panel. (Dozens of screws
> >> around the perimeter of the skin and six screws around the fuel filler
> >> neck
> >> is all that is stated to be removed). The skins would not remove after
> >> careful tugging and pulling. (the fuel cap was removed for this).Then I
> >> finally found three rivit type fasteners also around the filler neck.
> >> They
> >> apparently hold the skin in place in addition to the six screws but there
> >> is
> >> not any reference in the manual about removing them or drilling the heads
> >> of
> >> the rivits off. If they are indeed rivits, they are flush head type
> >> because
> >> they are smooth with the skin's surface. The heads are about 1/8th inch
> >> in
> >> diameter. I was hoping they could be merely some alignment pins. I
> >> removed
> >> the small inspection cover over the fuel transmitter (sender) to get a
> >> better grip on the panel near the filler neck. When trying to gently lift
> >> the skin panel upward, it is obvious that the three rivits are attached
> >> to
> >> the panel and to a flange underneath the panel that apparently secures
> >> the
> >> filler neck. The panel would not pop clear of them. So I don't think they
> >> are alignment pins.
> >> Anyone familiar with this to advise drilling these three fasterners to
> >> free
> >> the panel?
> >> Thanks,
> >> Tom Cummings




--

Tony Roberts
PP-ASEL
VFR OTT
Night
Cessna 172H C-GICE

[[email protected]]

Don't drill out those rivets! They are only holding a circular
gasket flange ring on the top skin. After all the screws are out, you
have to be a little less gentle with that skin and lift it enough that
the gasket flange ring will clear the tank neck and allow the skin to
slide out from under the leading edge skin and cabin roof skin.
Cessna wants those skins off every 1000 hours, and there's good
reason. We have found broken tank restraining straps, missing strap
chafe protection, rubber tank support and top skin straps rotted away
and the tank rubbed through (or almost through) against aluminum
structure, fuel stains around the filler neck weld indicating a crack
that could suddenly get serious, and so on. (Line boys with their big
fuel nozzles tend to let the tank neck take the hose weight, and that
cocks the tank neck and cracks the weld.) Once the mechanic has done a
couple of these inspections they're not a big deal. The skins are much
harder to get back into place thatn they are to take out, especially if
the tank was moved a bit; the filler neck will no longer line up with
the skin when the skin's screw holes are lined up with the wing's
holes.
You'll need a couple of new gaskets for the filler neck, at
typical Cessna prices.

Dan

[Tom Cummings]

Thank you very much Dan for the info.
Tom
> wrote in message
ups.com...
> Don't drill out those rivets! They are only holding a circular
> gasket flange ring on the top skin. After all the screws are out, you
> have to be a little less gentle with that skin and lift it enough that
> the gasket flange ring will clear the tank neck and allow the skin to
> slide out from under the leading edge skin and cabin roof skin.
> Cessna wants those skins off every 1000 hours, and there's good
> reason. We have found broken tank restraining straps, missing strap
> chafe protection, rubber tank support and top skin straps rotted away
> and the tank rubbed through (or almost through) against aluminum
> structure, fuel stains around the filler neck weld indicating a crack
> that could suddenly get serious, and so on. (Line boys with their big
> fuel nozzles tend to let the tank neck take the hose weight, and that
> cocks the tank neck and cracks the weld.) Once the mechanic has done a
> couple of these inspections they're not a big deal. The skins are much
> harder to get back into place thatn they are to take out, especially if
> the tank was moved a bit; the filler neck will no longer line up with
> the skin when the skin's screw holes are lined up with the wing's
> holes.
> You'll need a couple of new gaskets for the filler neck, at
> typical Cessna prices.
>
> Dan
>

[Doug Vetter]

wrote:
> Cessna wants those skins off every 1000 hours, and there's good
> reason. We have found broken tank restraining straps, missing strap
> chafe protection, rubber tank support and top skin straps rotted away
> and the tank rubbed through (or almost through) against aluminum
> structure, fuel stains around the filler neck weld indicating a crack
> that could suddenly get serious, and so on.
<snip>

I'll second that assessment. Tank skins need to be pulled far more
often than most people bother to pull them. The OP's mechanic is doing
his job.

See our recent experience on my site. Click through:

Aviation->Articles->Maintenance->Fuel Tank Repair

-Doug

--------------------
Doug Vetter, CFIMEIA

http://www.dvcfi.com
--------------------

[[email protected]]

Good article. Your airplane has an older style fuel cap and flange
arrangement than the original poster, and his skins are more difficult
to remove. His advantage is not having that recessed pit around the cap
that collects water and dirt; the cap flange is flush with the wing.
His disadvantage is getting that gasket back into place while replacing
the skin; a bit of fuellube will hold it in place. I suspect his tank
skin is being hard to remove because someone used Form-A-Gasket or
something tough to seal the gasket last time, and it's stuck good.
172s used all-brass floats by the time our L and M models came
out. They're OK, but we had one fail because the arm stop was
misadjusted and the float was tapping the top of the tank when the tank
was full of fuel. It wore a hole in the float, which filled and sank.

Dan

[Tom Cummings]

> wrote in message
ups.com...
> Good article. Your airplane has an older style fuel cap and flange

That is correct Dan. My cap is flush with wingskin. Once I get it the skin
loose,
the skin will slide across the neck.

> a bit of fuellube will hold it in place. I suspect his tank
> skin is being hard to remove because someone used Form-A-Gasket or
> something tough to seal the gasket last time, and it's stuck good.

Yes, I saw the hardened sealant when I removed the screws. There is
definitely
no way or place to pry or use a tool to losen the skin without ruining any
components so
it is going to be interesting.
\The Cessna manual calls for some specific types of sealant to use, one
being
a Dow Corning product, and others.
I have not ordered any gaskets yet as I am waiting to see if I to need any
other
components such as tank restraining straps, chafe protection, rubber tank
supports,
top skin straps, and the sealant.
Tom

[Jon A.]

Good one. Thanks!

On 24 Apr 2005 20:01:30 -0700, wrote:

> Don't drill out those rivets! They are only holding a circular
>gasket flange ring on the top skin. After all the screws are out, you
>have to be a little less gentle with that skin and lift it enough that
>the gasket flange ring will clear the tank neck and allow the skin to
>slide out from under the leading edge skin and cabin roof skin.
> Cessna wants those skins off every 1000 hours, and there's good
>reason. We have found broken tank restraining straps, missing strap
>chafe protection, rubber tank support and top skin straps rotted away
>and the tank rubbed through (or almost through) against aluminum
>structure, fuel stains around the filler neck weld indicating a crack
>that could suddenly get serious, and so on. (Line boys with their big
>fuel nozzles tend to let the tank neck take the hose weight, and that
>cocks the tank neck and cracks the weld.) Once the mechanic has done a
>couple of these inspections they're not a big deal. The skins are much
>harder to get back into place thatn they are to take out, especially if
>the tank was moved a bit; the filler neck will no longer line up with
>the skin when the skin's screw holes are lined up with the wing's
>holes.
> You'll need a couple of new gaskets for the filler neck, at
>typical Cessna prices.
>
> Dan