I will admit, there is very little info presented in the PDF file, but I’ll put on my plastic detective badge and take a W.A.G.
In photo 1, I agree. I don’t see any evidence of three-headed rivets, which suggests that gap occurred after the initial riveting. I concur about the significance of that gap.
What I find interesting, is the decision to use rivets in a stack up of aluminum that appears about an inch thick. In my experience, those situations, especially when involving spar caps, use Hi-Shears, Hi-Locks, or similar fasteners, sometimes with an interference fit.
A stack up that thick will absorb most of the hammering impact of a pneumatic rivet gun. It appears this is what happened initially, and the guy riveting, switched to a much harder hitting gun, which created the numerous skin divots visible in the 2nd photo. Those divots are a huge red flag, and after the first 2 were created, the riveter should have been on the phone with the engineer, to devise a better solution. The inspector who OK’d that riveting mess, before paint, should turn in his IA.
I am surprised to see fretting corrosion (smoking rivets) in photo 2. Assuming this is a low time airframe, that suggests an extremely poor fit up of parts and/or sloppy riveting.
In photo 3, the countersunk rivet heads, that are well below the skin surface, suggest incorrect countersinking, either by the factory or the assembly shop. The riveter should have called someone on this after discovering it. Perhaps he did, and had a shop manager tell him to shut up and get the job done. I’ve known shop managers who thought two bricks were sufficient to shoot solid rivets.
In photo 4, the deformed rivet shop heads suggest an untrained individual, which is common in sheet metal repairs, where the dumbest guy is usually chosen for the “dumb” job of holding the bucking bar. I’ve tried convincing shop managers that is not a smart move, but am rarely successful. I often stack up scrap skins in a vise and give the dumb guy some OJT before we tackle the aircraft.
The sheared rivets in photo 4 suggest the aircraft was over stressed in flight or during an accident, or the rivets were an insufficient fastener to handle normal shear forces. I’m gonna go with a W.A.G. of insufficient shear strength.
I’m not surprised at this quality of structural work. Although it is below the level of 95% of the factory workmanship I’ve seen, it is actually above the standard I see in many shop repairs.
I will now put my plastic detective badge back into the cereal box.