|Well, we are going through some of those additional inspections right now on our 337. For the most part, I've found that they are simply duplicating inspections that you should be doing in the first place, but highlighting problem areas and doing a little CYA for what they specifically want you to inspect. I think they also want to increase the maintenance requirements on these aircraft to hasten their retirement.
We thought it was a lot of BS at first. The only other time I've seen CPCP programs was on turbine aircraft with things like lavs and thousands more hours and cycles in corrosive environments. Our planes get spoiled being in a dry-belt and hangared all the time. The only time I fly in rain is when I want to give the bird a good wash.
I expected to find corrosion on the elevator and horizontal stab, as it is in the exhaust efflux from the rear engine. Minor surface stuff only.
What I didn't expect to find was the massive amounts of corrosion on the leading edge wing root rib on this two-bit inspection item that should have taken me 30 minutes to complete....
I got lucky and found a rib used where the holes line up and Cessna never got back to me on a new one (I at least wanted to have a chuckle on the price, I was betting at least a grand and maybe two) Good luck making one from scratch, 0.050 2024 T6 with compound bends and joggles---you'd need a bloody drop forge!. Everything goes through it (fresh air vents, R/H fuel selector tele flex, aileron balance cable, all of the wiring, and a fuel cross feed line), plus it picks up the fwd wing fitting and the fasteners go through the main spar and required the removal of the R/H aux fuel tank. I've found out that the 3/6" x 7/8" Hi Locs that go through the spar are a rare commodity with a 30 day lead time and had to buy two bags of rivets for want of four dash 6 (3/16") rivets I did not have in my stock.
Just a little taste of how even a basic re and re of a structural member can turn into a clusterfuck. Gear fittings on 172s are way easier. I hope to have it wrapped up by Christmas...
If you get a plane with a bit of surface corrosion inside (white powdery residue), just leave it alone. It looked like that ten years ago and it will look the same ten years from now on a light aircraft. That is the ALCLAD doing its job. As soon as you attack it with scotch brite (the brown aluminum-oxide pad, don't ever let me catch you using a green pad on a plane!) you will be fighting even worse corrosion the next time. Then the scrub, etch-alondine, prime, and CPC cycle that ends when the part disintegrates or you run out of money or sanity.
Also, for those extra inspections, make sure you pay attention to the hours and calendar requirements. On ours for the removal of both the wings and the tail booms, it said 12,000 hour or 20 years (they are all over 20 years), but, it said that for aircraft under 12,000 hours, you could do a basic visual and if there were no defects, skip the detailed inspection. Saved a ton of work not having to pull those off....