The Cessna 120-140 Association Forum

Does anyone know the origin of the Rear Spar carry through inspection holes in the cabin roof ? Did Cessna call for these ? I have them in my 120, they seem like a good start towards installing the Wag Aero type Shoulder Harness. Two would need to be enlarged to the 5/8" dia called for in Wag Aero"s installation instructions. Anyone had the experience?

6319 wrote: ↑Fri Jan 31, 2020 8:05 amDoes anyone know the origin of the Rear Spar carry through inspection holes in the cabin roof ?

I have never seen anything like these. Sounds like a one-off to me. If they're smaller than 5/8" they wouldn't be very useful, I'd think.

That said, it is possible to install the Wag Aero kits without making holes in the cabin roof if you have the wings off. The secret is a box wrench taped to a long stick...

I have the same inspection holes fore and aft, here's an attachment from a 1982 Association newsletter. I think the Luscombes had something similar at one point. I replace the plastic plugs every two years after I shoot the insides with ACF-50 with an atomizer. I'll see if I can find some more info...

And here's the Luscombe AD that started it all....

Thanks David, Did you go with the Hooker Harness , regardless of these holes ? They may not be in the proper location, Wag Aero calls for 11 1/4" from the side skin inwards for their 1/4" hole to be in center line with the seat back. Appreciate the info and attachments.

The plane came with the Wag-Aero arrangement, I'll have to measure a few holes and see how they did it. The interior attach points do not directly match with the inspection holes I know that much.

I haven't measured mine but have the feeling they are not exactly where required, (what a coincidence if they were). Perhaps as John suggests the wings were off when yours were installed. I talked to Jack Hooker at Sun-n-Fun a few years ago and he made the comment "another one with holes in the roof". Like you I take a look in and spray some Corrosion X occasionally.

The carry through spars can have two issues I'm aware of.

1. Corrosion. Remove the headliner or pull it down enough to see the carry through spars. If you have corrosion typically it manifests by white powder leaching out between the roof skin and the edge of the carry through spar skin. (where the two skins meet on the bottom of the roof skin) As far as corrosion inside the carry through spar, down in the lower sections of the carry through if you will, I haven't seen it, but..........with the age of our aircraft and unknown past of your airplane (i.e. sitting outside, or in a salt air environment....) anything is possible.

I would be careful about drilling holes in the roof and then plugging them. Sometimes the cure is worse than the original problem? (suspected problem?) I know it's work to remove a wing and then pull the inner blocks, but I think I would be inclined to do that before I bored holes in my roof. Corrosion is slow building issue and pulling your wings once every 10 years or so would probably do it? I'm always cautious about not creating problems in my zeal to "fix" problems.

2. Cracks. This is an issue with the forward carry through, more so than the aft carry through. Typically found between the small bolt holes on either side where the door post attaches. Almost always associated with float planes. 10-15 years ago Jack Hooker brought a carry through spar to Oshkosh that was cracked badly between the small bolt holes. I've taken every opportunity to look at visible spars in that area on any airplane I can (including my own by removing the wings and the spar blocks) and have not seen any more cracks like that. Not to say they don't exist, but I have a deep suspicion that those cracks come from the 'see saw' motion that a float plane would experience and a land plane would not.

I hope this helps someone.......

Thanks Victor.