Carry-thru spar corrosion

[PilotDAR]

Guess where I found this? Cessna manuals

I agree, the data is in the Cessna manual, though presented as a Supplemental Inspection Document, which believe to not be mandatory on private airplanes. But, the SID provides helpful data, which the main Service Manual does not contain. Thus, it is a valuable resource!

As it is a "method recommended by the manufacturer..." it is "acceptable data", which is appropriate as long as the repair is not "major". Using the SID data as a reference, as long as the repair is within the 10% material thickness, it is not major, so the data is applicable. Were the material being removed in this case exceed 10%, it would be a major repair, and require approved data, as stated in the SID, as the SID data would no longer be applicable. It looks to me that the OP's 150 would be within that 10%, subject to confirmation by measurement.

Note that the 10% allowable is not applicable to all structural parts. I know of some Cessna parts with much more restrictive allowables.

NDT will be required to check thickness post corrosion removal

I opine that the material removed could be measured without requiring an NDT process. I can't see where the SID tells you how to measure material removed, just that you must.

The SIS is voluminous, and filled with useful information. The only part of the C 150 SID which I find to be not applicable, is the fact that on page 178 of 208, the image of the airplane under the title "Model 150 Series" is a 177 - oh well...

[Dash8-400]

Pilotdar- that is correct!

Many items on the aircraft do have tighter tolerances for corrosion removal (aka less then 10%) as this is why I always recommend to check the manufacturers manuals that are current before using AC4313.

I reference I found for the inspection / repair was NDT to be used ( ultrasonic method to check thickness). To make that reference legal you would have to follow it to the T AKA NDT measurement after.

Once again if the corrosion is past limits. The next step would be to contact Cessna and with the numbers and see what they can do! Like PilotDAR mentioned it would be a major repair ether a splice or full replacement of the corroded item.


Regards,
Dash8-400

[boeingboy]

Mirobot200 so the inspection of this area is called out initial in 2 forms:

Heavy corrosion : 10 years initial
Repeat every 5

Light corrosion: 20 years
Repeat every ten.

So this is why you wouldn’t really look on the annual

Except for the fact that you open the zipper to inspect the cables, the pullys, and the surrounding structure….you really would just ignore the corrosion on the structure?

[Dash8-400]

Boeingboy, I would agree with you. Me personally doing the annual I would. But other Ames have different mindsets as I’m not suppose to inspect this area so they use tunnel vision and only cables and applicable items to the annual.

It’s a typical debate that’s been on going for many years. Guys say if it’s not in the package I won’t check it, so if it’s a common issue Cessna needs to reduce the inspection time between checks.

So this being said this is where SDRS and other forms of reports need to be submitted to the aeronautical governing body and to the manufacturer.

This corrosion isn’t new at all from what I can tell from the pictures.

Regards,

Dash8-400

[rxl]

AVCANADA at it’s very best!

[mirobot200]

Apologies for the radio silence, I was away for work and just got back home a week ago.

Thank you PilotDAR and Dash8-400 for your very informative replies. PilotDAR, to answer your question it's a 1961 150A model.

The local AMO inspected and cleaned the corrosion while I was away, and from what I understand also consulted with Cessna, and signed off on it. I think it was right at the limit. Next week when I'm out of quarantine I'll go pick up the logbook and look over the aircraft, and discuss with the AME what was done in more detail.

I do have some 250 pages of Supplemental Inspections and Corrosion Prevention and Control Program in my AMM that I've been going through. I don't believe any of them have been carried out yet, but I will have the more critical areas inspected and signed off at the next annual. The plane seems to have fared well considering it's age, but it was operated in the interior. Now, being on the coast and all that salt in the air, I'll have to keep corrosion prevention on my mind. Maybe spray some ACF50 or LPS3 on the structure.

[PitchLink]

One word.... Alumagrip.... LOL

[Dash8-400]

That’s good news!

[PilotDAR]

One word.... Alumagrip

On the outside of the plane, yes. On the inside, following assembly, not so fast... If paint inside and outside could result in the joints being sealed, anti corrosion liquids applied cannot get in, and moisture or corrosive elements are held in. If I have a local area with corrosion, which does not include a joint, then yes, I might prime it after cleaning. But I would rather not seal a joint with really good paint.

I've been told that the French built Cessnas internal corrosion prevention primer was sprayed in following assembly, and as such, had only a modest benefit. Other types I know were assembled from parts primed before assembly, and did much better.

At this point in their lives, legacy GA types which left the factory bare inside are probably best corrosion protected with a suitable corrosion prevention liquid (ACF50 being one example). It'll work itself into the joints, and really do its job there. Paint, once dried, at best seals where it is. Maybe better than nothing, but maybe not the best either....

[Dash8-400]

I agree with pilotdar.

Another to add if prep of paint is poor it will seal and eventually bubble with corrosion.

Use ACF50. Check on periodically as next time it corrodes it will be expensive!

Regards.
Dash8-400

[oldncold]

my plane. cessna177 is in for new paint. they found a fair bit of the corrosion exactly as expected in Cessna service letter in sel-57. I'm so peeved at my ame that he didn't catch that on the prebuy inspection.. so awaiting reply. from paint shop and the company structures rep to see what the next move should be cost wise.

Cessna is quoting 45k usa dollars for new carry thur spar. though my guess it is new old stock. they built in the 70's for. 10k. feel your pain.

[mirobot200]

Cessna is quoting 45k usa dollars for new carry thur spar.

Ouch! Good luck I hope they find a cost effective solution for you.

[PilotDAR]

I'm so peeved at my ame that he didn't catch that on the prebuy inspection.

The 177 spar is a completely different thing than that of all other Cessnas than the 177 and most 210's. The SEL you refer to gives very specific direction as to what to do if corrosion is found on the fuselage spar. There really is no way around their instructions. It is important now a days that pre purchase instructions include inspecting as described in the Cessna SIDs for corrosion, and referring to the applicable service letters.

Remember that Cessna did not build these planes thinking that they'd ever be in service this long, so now they are playing catch up with inspections which should always have been required.

One of my clients has recently changed a spar in a 210, which was a considerable job. I expect to test fly it tomorrow, and then issue the approval for the spar change. It was necessary to do a distinct approval, as for the 210 (and I expect the 177 as well), the service manual tells you that you need more data than the service manual provides.

Buying a carry through spar for a 177 or 210 as a part is only a part of the solution, replacing it is not straight forward. For all other single Cessnas, it's straight forward, though still a bunch of work.

[oldncold]

thx pilot dar. I was fortunate to take it to a paint facility that has the structures authorization and technical capabilty. to carry out the the quality of repair needed but it isn't going to be an. easy$ pill to swallow. I've saved some $ by already having the plane wings taken off in anticipation of the new paint now on a holding pattern and the labor won't be. duplicated. with out the new carry thru the plane won't ever be airworthy. and negates the rest of the plane which is in. solid condition. takes a lot to get oldncold peeved after all these decades but this is doing that. but. as they say say. focus on the future aviate navigate communicate.

[Dash8-400]

Unfortunately Ames are like car mechanics. There’s a tone of good ones and bad ones. You really wanna find someone who specializes On a few aircraft instead of a GA guy. I have found numerous issues related to SBs snd ADS for cracking / corrosion ect that jack of all trades ame miss.

Good luck on the paint and hopefully you can give your ame shat for this one.