A B747-400 HAD A TUBING SUPPORT FITTING REPLACED DURING A MAINT CHK BY A CONTRACT VENDOR. DURING FLT OPS; CREWS RPTED ACFT LEVELING AND STEERING PROBS. FOUND 2 HYD HOSES CROSSED.

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DURING A MAINT CHK ON ACFT INSPECTION; I FOUND A HYD TUBING SUPPORT ON THE L-HAND WING MAIN LNDG GEAR; REF IPC 32-53-11-06 TO BE DEFECTIVE AND NEEDED TO BE REPLACED. THIS TUBING SUPPORT; SUPPORTS ALL THE #1; #2; #3 AND #4 BRAKE HYD HOSES; THE LEVELING AND STEERING HYD HOSES ON THE INBOARD (BODY) MAIN LNDG GEAR. THE MAINT MECHS REPLACED THE DAMAGED PART ACCORDING TO THE SRM 51-40-02; IPC 32-11-06 AND MAINT MANUAL 29-11-00 -- THE REGULAR LEAK CHKS WERE ACCOMPLISHED. THE ITEMS WERE SIGNED AND BY-BACK BY A MAINT SUPVR AS THE MECH THAT PERFORMED THE JOB IS AN UNLICENSED MECH. I PERSONALLY CHKED AS AN INSPECTOR AND THE ITEM WAS FINALIZED AS A GOOD REPAIR. AFTER THE SECOND FLT; THE FLT CREWS STARTED TO OBTAIN DIFFERENT LIGHT INDICATIONS OF ACFT LEVELING AND STEERING SYS PROBS. FINALLY; IN ANOTHER STATION THE ACFT WAS PUT ON JACKS AND THE LNDG GEAR WERE SWING TESTED. WHEN THE GEAR WAS SWUNG; THEY FOUND OUT THAT THE 2 HOSES CROSSED (THE LEVELING CYLINDER HYD LINE AND THE STEERING CYLINDERS RETURN HYD HOSE) ON THE ITEM THAT HAD BEEN PREVIOUSLY REPLACED. THE MAIN CAUSE WAS THAT THERE WERE 2 MECHS WORKING ON THE SAME ITEM -- ONE DOING THE REMOVAL AND ANOTHER MECH DOING THE INSTALLATION AND THAT THERE WAS NO COM BTWN THEM. AND THAT THE SYS INSTALLATION WAS NOT PROPERLY CHKED BY THE MAINT SUPVR ACCORDING TO THE MAINT PROCS.