Assorted test fit of side and bottom skins

It was found that the rear bottom skin holes aft of rib 5 suffered a drift on the left side, such that they mismatched both the longeron and the rear side skin (which themselves matched). This drift reached a maximum of about 0.8mm at the rearmost rib 7. The alignment on the right side was perfect. Since the rear bottom skin is a middle layer, an elongation of the hole by match reaming is unacceptable as the rivet has the capability of swelling to the degree required at the tail only. Discussed with Sling, agreed that upsizing to 4mm rivets is an acceptable fix.