The International Cessna 170 Association

The new proposed AD note on lower doorposts/lower strut attach area of single engine Cessna airplanes does not apply to the Cessna 170 series.

It is the result of cracks found in several dozen 172N, 182E and later models as well as 206/207 aircraft. It will recommend a repetitive inspection of aircraft with more than 4K hours and a repair scheme if cracks are found.

https://www.gpo.gov/fdsys/pkg/FR-2018-0 ... -01923.pdf

Comments open till March 19, 2018............

gahorn wrote:The new proposed AD note on lower doorposts/lower strut attach area of single engine Cessna airplanes does not apply to the Cessna 170 series.

It is the result of cracks found in several dozen 172N, 182E and later models as well as 206/207 aircraft. It will recommend a repetitive inspection of aircraft with more than 4K hours and a repair scheme if cracks are found.

https://www.gpo.gov/fdsys/pkg/FR-2018-0 ... -01923.pdf

I get that the AD did not list 170's but I wonder (quietly... sssh!) "Why not?' I understand that we are somewhat protected by smallish fleet size, which makes it more difficult administratively for the FAA to document a widespread problem worthy of an AD. However, is there something fundamentally different about our birds and the ones listed, or should we also be just a bit concerned even though we were not included in the AD?

Brent

Humm...(again), not a bad question or bad idea to fully understand what the problem is. Model and serial number suggest it's models that have a lighter aft door post that are affected. Does the lighter aft door frame somehow have an effect on the the forward structure? I wouldn't think so but maybe the latter models also have a lighter front structure than our machines. I'm wondering about my XP, it's s/n 1723135, a 79 model which appears to have missed the calling but how is that possible? Unless of course someone has a problem with their keyboard

The gross wt of the aircraft would impact this, as would any change in sheet-metal ga., increase in wing-loading....(think fuel capacity/weight)... or operating speeds...(think "turbulence penetration"), etc. etc. The affected aircraft also have their gearboxes moved to the rear doorpost (they are all "tricycle-gear")... so the shock-wave at touchdown would be transmitted differently to the wing-structure/attach area, with the added phenomenom of "twist" applied as well considering the arm of that force.

The area in question is an area which should be regularly inspected in accordance with the 100-hr/annual inspections anyway. If cracks are found...they should be reported by the owner/operators.

Could also be that because the 170 has the gearbox structure almost right under that area making it less vulnerable. All the other aircraft in the AD have the gearbox further aft.

different lower wing strut attach point on bulkhead, nose wheel airplanes included in the AD use a fitting to attach the strut to.

To illustrate the difference in the affected later model 172's vs. the earlier model 172's........
For the 172 series, the AD is effective beginning with serial number 17272885, which is the last year of the "N" model. Difference is obvious.

lowNslow wrote:Could also be that because the 170 has the gearbox structure almost right under that area making it less vulnerable. All the other aircraft in the AD have the gearbox further aft.

That was the major point I was attempting to make when I wrote:

gahorn wrote:... The affected aircraft also have their gearboxes moved to the rear doorpost (they are all "tricycle-gear")... ....

Del's excellent post also demonstrates the structural differences between the early vs late serials of the affected models.

Thks Del, hadn't seen the tech data on the proposal, looks my 172XP was old school, how fortunate, could it be worth more now?

Del's post says it all, thanks.

With similar door post/gear box sections as the C-170, but without struts, C-195s have cracks in the narrow section at the top of the front door posts which are corrected with an STC'd stainless steel patch strap worked-in between the outer skin and the door post.

I wonder how Cessna will correct this current design flaw?