Check the TOP of Your Aircraft

Ernie Martin · #1 02-07-08, 02:16 PM

I get to the airport at 7 AM so we can get an early start on two days of puddle jumping to several Bahamian islands. After a thorough pre-flight inspection and filling the tanks to the brim, I climb on a ladder to add a 1/2 quart of oil to the rear engine. While there I survey the top part of the aircraft: wings, fuselage, booms, elevator, etc. I am shocked to see an entire line of rivets missing -- gone -- near the front end of the rear engine scoop (see figure below). My shock was not just because I was surprised to find this condition, but the realization that it had been like that on earlier flights and my concern that the top panel could simply peel off, strike the rear prop, and cause a life-threatening accident.

We had done the annual inspection only a few months back. I had participated daily. And I couldn't recall, on that annual or any previous annual, anyone actually climbing on top of the aircraft to inspect it thoroughly. A cursory look, yes. A thorough inspection, no.

I don't know what caused these rivets to slowly disintegrate (you could see the shaft of some, without the head, so it's not that someone forgot to replace them), but it merits a good look on your aircraft. And I wouldn't wait for the next annual -- I'd do it before the next flight.

Ernie

Jerry De Santis · #2 02-07-08, 08:58 PM

Thanks Erine, I'l check mine next time I go to the airport.

Jerry

Skymaster337B · #3 02-07-08, 09:24 PM

I'm very curious, were there any nicks in the rear prop?

Kim Geyer · #4 02-07-08, 09:42 PM

We have had 2 with the skin peel up. One of them even tore the skin down the side. The one I'm working now has 3 missing rivits.
My fix is to drill out all the rivits,cut strips of .032 alum. for doublers and use screws and nuts. reriveting is most likely not going to work because the inlet is fiberglass and the rivits will just pull through. It's not too bad of a job, you'll scratch your arm all to heck getting the doubler and the nuts started.
Hope this helps
Kim

Ernie Martin · #5 02-07-08, 10:31 PM

No nicks on the rear prop. Good suggestion by Kim to replace with screws and nuts. If Kim is right and the fiberglass inlet causes the rivets to pull through, then a recurring inspection every time you add oil to the rear engine may be prudent.

Ernie

skymstr02 · #6 02-08-08, 12:35 PM

Quote:

Originally posted by Ernie Martin
I
I don't know what caused these rivets to slowly disintegrate (you could see the shaft of some, without the head, so it's not that someone forgot to replace them), but it merits a good look on your aircraft. And I wouldn't wait for the next annual -- I'd do it before the next flight.

Ernie

Those rivets originally installed by Cessna are "A" suffix rivets, which mean that the alloy is 1100 aluminum. This means that the rivets are dead soft aluminum, not alloyed with copper, so they have no structural shear strength at all. This is common to join aluminum sheet with fiberglass in order to not damage the fiberglass when the rivet is set. It doesn't take nearly the same effort to set the bucktail on an 1100 as it does a 2117 (structural) rivet.

This is a common occurance on an aging aircraft and deserves special attention on routine shop visits.

As the Skymasters age, the inspection techniques used 30 years ago need to be augmented to account for this aging.

Skymaster337B · #7 05-18-08, 09:02 PM

I found a single rivet head missing from the same location, today. Does anyone know what type of rivet is used to replace it? Can I use a cherry max, if so what kind is it?

Thanks,

Kim Geyer · #8 05-19-08, 08:48 PM

I think from the factory they are just AD rivits but when they are bucked there is a washer on the inside to keep the rivit from pulling through or cracking the fiberglass.
I have used cherry rivits but you still need the washer on the inside or it will just pull through the fiberglass and then you will play hell trying to get it out.
Kim

Skymaster337B · #9 05-20-08, 01:02 AM

Thanks for the help. Would you happen to know what the AD number is for the rivet and/or AN number for the correct size washer? As well as the AD number for the correct cherry max rivet?

Thanks.

Mark Campbell · #10 05-20-08, 01:11 AM

What do you know I was looking at the Top, on one of my return trips home, and what do you know! a slight tap up came 5 or so small circles, All replaced with an upgraded fastener so this was a great catch. Good on you, Lets keep the last of the 30,000 club alive for my Turbo Brothers out there. RVSM any one if I can get 10 or more I know the process, Just a thought!
All the best!
A twin Tail in sand
Mark