Here is a little history.
We (the non-scab techs) spent many years replacing primary structural components in the DC-9 starting in the late 1980's and early '90s. We replaced bulkheads, skins, main frames, landing gear attach fittings, keel beams, spars, etc...this in addition to the aging aircraft mods (window belt doublers, station 83 mods, sids....) When NWA made the decision to keep the DC-9's for the long term, we stepped up to the plate and delivered. We wrote the book on many repairs for Douglas. Douglas and the FAA used our DC-9's as case studies in structural repair perfection. Many of the repairs were simply done by the techs, then the Engineer would come and draw up what was done and submit it to the FAA and Douglas for approval. These guys were good.
Most of this heavy work was done in ATL in the old Southern/Republic Hangar. NWA hired many Ex-Eastern mechanics (250+non-scabs) who had been working on DC-9's since they were delivered. Those guys, in addition to the old Southern/Republic talent made the DC-9 fleet able to fly another 15 years.
I had the pleasure of working with some of the finest Aviation Sheet Metal/Structural Repair Technicians in the industry. They/us were second to none in ingenuity and engineering know-how.