Yes; various threads.
Whether this one can be thus repaired I have no idea. You need to ask Socata/Daher.
IIRC Daher can issue a repair plan based on documentation of the damage, might be worth reaching out to them.
I wonder what factors contribute to this type of corrosion, has is been stored outside for extended periods?
That looks pretty dramatic corrosion! Especially where it is – at the max stress part of the “I” beam
Hi there,
we have a club owned TB20Gt from 2000, serial# 2004.
During our annual I looked deeply along the wing spar for corrosion, knowing it is a spread problem amongs TB’s. We already had corrosion in the horizontal stabiliser and repaired it.
I found 2 spots of exfoliant corrosion at the main spar this evening, one in each wing. Is this considered severe corrosion? It must have been undetected all the previous years.
https://postimg.cc/N9v5wJZ7
https://postimg.cc/8F6j9QXz
https://postimg.cc/w1P1wTVr
https://postimg.cc/svTQZJZs
I would be very happy to get some information on what the repair procedure is (or are the wings a write off?) and what kind of money is involved?
All the best,
Patrick
[ dead image links replaced with URLs but that site doesn’t obviously serve jpeg image links, but while you can get them with a right click, this way you get hi-res pics ]
I got this reply from Socata:
Silvaire wrote:
I imagine they’d need to redo the stress and fatigue analysis
Not necessarily: A lot of aviation certification work is done based on previous approved data. All you need to do is show that it is better in stress and fatigue fronts and not take credit from any of that. Perhaps flutter tests are required due to different modes/freqs though .
Peter wrote:
Could it be that Socata had a load of 7175 lying around from their Airbus subcontract work?
Could be, but I imagine they’d need to redo the stress and fatigue analysis so there would have to be enough of a benefit to pay for that.
You’ve just reminded me of a trip to an aerospace quality machine shop near Los Angeles circa 1993 
If I recall all the details correctly they had a huge bridge mill and were machining one piece Airbus main spars. I haven’t thought about it in years but you don’t often move a machine like that. Note reference to 308 ft bed length, which is a lot bigger than our planes!
Could it be that Socata had a load of 7175 lying around from their Airbus subcontract work?
If this change happened say 2000 then it would mean most GTs had this spar material. It is unlikely to have happened much later because by around 2001 the internal decision was made to drop TB production, and 2002/2003 aircraft were made from a pile manufactured mostly in 2000/2001.
Yes, 7175 (or 7075, I don’t know what the practical difference is) is definitely “spar material”, more so than 2024.
The 6061 is just me wondering about the benefits of it compared with 2024, which are two very different materials.
Nothing like the same, at the opposite ends of the strength and cost spectra. Here is a bit of background. Most of what is described for 7075 applies equally to 7175. 7000 series alloys are quasi-exotic aircraft material.
I think 6061 was mentioned here because it’s inexpensive, well known, widely available and has been used recently in UL aircraft, without much weight penalty if the structure is mostly designed for stiffness or practical minimum skin thickness, not strength. That may be the case for e.g. boxy thin wall structures as opposed to wing spars. 7175 is conversely a high strength alloy, similar to 7075, expensive but good for highly loaded structure like wing spars. 2024 is in between, the workhorse alloy for aircraft. All of the above aligned with what @LeSving posted.
