What was found
AFTER GEAR RETRACTED SUCCESSFULLY & CLIMBING ABOVE FL 400, FELT A THUMP IN NOSE. RECEIVED MAINS UP & NLG MISCOMPARE AMBER MESSAGE. DESCENDED TO A LOWER ALTITUDE. FELT MORE STUTTERING THUMPS. AFTER THAT A RHYTHMIC THUMPING. LOWERED FLAPS 1 & ABOUT TO LOWER GEAR WHEN IT STOPPED & SHOWED UP. LANDED SAFELY. NO DAMAGE TO NLG OR BAY. DISCONNECTED DOORS, PERFORMED GEAR SWINGS. FOUND NLG UPLOCK SWITCH NOT ENGAGING. PERFORMED GEAR BUMP TROUBLESHOOTING. CHECKED PSI OF UPPER & LOWER BARREL. FOUND BOTH BARRELS LOW PSI. SERVICED UPPER & LOWER BARREL OF NLG STRUTE. MEASURED STRUT LENGTH & FOUND GOOD, RECONNECTED NLG DOORS & PERFORMED SWINGS, GOOD WITH UPLOCK ENGAGING PROPERLY. WORK DONE IAW AMM 32-00-00,12-10-52.