Welding Tips and Tricks

I'm currently monitoring the repair of a 40 year old abandoned airplane on Youtube. Some corrosion has been found. They claim the repair will take well over 100 hours to replace the part that will take 9 months to get from the manufacturer. My question is, if the damaged part is accessible, why can't the area in question be cut out and replaced by a certified welder.
They say NO because it is not the manufacturers recommendation. Just because the manufacturer doesn't approve it doesn't mean the FAA wouldn't allow it. I would like to hear some thoughts on this.

Chip

This reply is not meant to express an FAA or aviation-certificate level response. But in general…

Any time a manufacturer recommends against a repair and instead dictates a replacement it is generally categorized in two camps: liability and engineering. From a liability status, even if the repair were performed by a certified welder, the manufacturer must issue the WPS to meet their design criteria, fatigue, stress, etc. Failure to abide their procedures can negate your claim against them for liability from design and wear.

From an engineering perspective, the part may be subjected to stresses, heat treatment, etc that a patch-welded repair won’t meet the design demands. Again, goes to liability. But you should also consider their engineering process to determine the final product and whether a weldment after production suits the fabricated part/assembly. It does not always meet the criteria.

None of the above is a declaration of wrong or right about your particular scenario, but I for one would not be willing to void any liability on an airplane (if one still exists 40 years later?) structure from a pure safety perspective.

I was an IA for years. Any repair must be based on approved data. AC43.13 is considered acceptable if not in disagreement with service manual. If the service manual disallows the repair, it is very unlikely that someone from the local FSDO will sign off a field repair. At this point, about your only option is a DER. I have had to go that route in the past, to repair a cracked spar on a C-310. Once the DER issued us the 8110 form, the rest of the paperwork went pretty easy. Of course the 8110 was costly.