[wslade2]

I did CiES probes and took all upper panels over the tanks off last year. Out of those hundreds of screws, I think one of everything that could complicate it happened.

Did a screw head break off? Is there a retained screw shaft? There are 4 screws in the fairing you are talking about with 4 countersunk washers. Be sure all 4 screws are out. If less than 4 screws are removed, it is possible a head came off and the screw shaft is hanging you up. Hopefully nobody cheated and put a blind rivet in any of the holes (you mentioned it is riveted down but not if any rivets look like they pass through the panel). If either, it will have to be drilled out. Be careful about drilling out and use drill bit smaller than 10-32 screw. Preferably a reverse bit. If you can see a shaft, get an ease out in it if possible and plenty of oil soaking. The screws screw into wing rib with either nut plate you can't access or a tap into the aluminum itself. You will need to preserve the diameter of the hole so you can go back in with a tap or helicoil depending on the situation if things are buggered up.

It takes some wiggling, lifting and slight bowing of the panel to get the cover off. Also, it can get hung up on some burs, recesses/flush head dimples, imperfections. I found some aluminum flashing and wide putty knives/scrapers from hardware store useful to slip the panels in and out so they wouldn't get hung up on these and to lift away overlapping aluminum. The space the panels slip into are tight. You will see in my photo I had a screwdriver lifting up the boom fairing you are talking about at one point, upper left hand of photo.

To make my future life easier, i put a dab of fuel lube on the screws when they went back in. This also saved stripping out the screw holes. Start them all by hand. Don't get over zealous with a power driver and strip anything out. If using a power driver, preferably one with a clutch.

BTW-while there check your tank vent. For the aux tanks, in the connector fitting, they placed a small diaphragm with 3 pinholes in it. These pinholes easily get clogged blocking off the vent.