What was found
(CAN) RT MAIN GEAR FAILED TO EXTEND. THIS WAS DUE TO RIVETS ATTACHING UPLOCK BRACKETS P/N 40616-01 & 40616-02 SHEARING. THIS MAY HAVE BEEN DUE TO CORROSION. THIS ALLOWED W8 OF LDG GEAR TO PULL RIVETS THROUGH 2 ANGLES P/N 40625-00. AS A RESULT OF THIS, A MISALIGNMENT OF UPLOCK HOOK WITH UPLOCK ROLLER CAUSED UPLOCK HOOK TO JAM. THIS PREVENTED GEAR FROM EXTENDING. PILOT WAS ABLE TO FREE GEAR BY APPLYING POSITIVE & NEGATIVE G LOADS ON GEAR. GEAR THEN EXTENDED NORMALLY. UPLOCK BRACKETS HAD BEEN MODIFIED WHEN BOUNDARY LAYER RESEARCH STC-SA 00202SE SUPER CHIEF II WAS INST & AGAIN WHEN BOUNDARY LAYER RESEARCH SB- BLR 105 WAS COMPLIED WITH.