What was found
NLG DID NOT RETRACT WHEN GEAR HANDLE SELECTED UP. EMER & ABNORMAL PROCEDURES CHECKLIST FOLLOWED & GEAR WAS SELECTED DOWN. MLG EXTENDED & GREEN BUT NLG RETRACTED & HAD RED UNLOCKED LIGHT. TOWER VERIFIED MAINS DOWN & NOSE GEAR UP. EMER LG WILL NOT EXTEND PROCEDURE DID NOT BRING THE NLG DOWN, EMER DECLARED & ACFT ROUTED TO MKE. ACFT MADE A NLG UP LANDING WITH NO INJURIES. NLG SPADE DOOR & LT GEAR DOOR REMOVED & VISUAL CONFIRMATION WAS MADE THAT NLG UPLOCK WAS RELEASED. HYD LINES WERE CRACKED ON THE NLG & GEAR EXTENDED & VERIFIED AS LOCKED. INITIAL INVESTIGATION REVELS FLEXIBLE HYD LINES WERE POSSIBLY SWAPPED DURING RECENT IMPLEMENTATION OF SB680-32-06 NLG ISOLATOR PIN REPLACEMENT.