A DC9-30 RETURNED TO THE FIELD DUE TO INABILITY TO RETRACT THE R MAIN LNDG GEAR CAUSED BY CROSSED HYD LINES ON THE RETRACT ACTUATOR.

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AT APPROX XA30 MAR/XX/97; I WAS ASSIGNED ALONG WITH ACFT MECH ZZZ TO REMOVE AND REPLACE THE R MAIN LNDG ACTUATOR ON THE ACFT; A DC9-30 FLT; DUE TO A LEAK AT THE GLAND NUT. MAINT MANUAL PAPERWORK WAS OBTAINED AND STUDIED. INSPECTOR INSPECTED THE NEW ACTUATOR PER IPC; PART NUMBER AND EFFECTIVITY. MR XYZ REMOVED THE LEAKING ACTUATOR. AFTER CHANGING THE SWIVEL GLAND; HYD LINE AND RESTRICTOR OVER ONTO THE NEW ACTUATOR; I INSTALLED THE ACTUATOR PER MAINT MANUAL USING THE ALTERNATE METHOD. I INSTALLED THE HYD LINES TO THE SWIVEL GLAND WITHOUT EVER REMOVING THE LINES FROM THE STAND OFF BRACKET (BOTH SUPPLY AND RETURN LINE ARE SECURED TO THE BRACKET WITH ADEL CLAMPS). BOTH LINES USE THE SAME SIZE MS FITTINGS. AS PER MAINT MANUAL; WE CYCLED THE ACTUATOR 10 TIMES TO CLR ANY TRAPPED AIR AND CHK OP. MR ZZZ OPERATED THE GEAR HANDLE FROM THE COCKPIT; GATE MECH XYZ GAVE DIRECTIONS AND CLRNC FROM THE GND USING THE ACFT MAINT INTERPHONE; AND I HELD THE ACTUATOR CYLINDER CLR OF STRUCTURE AT THE WHEEL WELL. THIS PROC WAS OBSERVED BY INSPECTOR. AFTER CYCLING THE ACTUATOR; CYLINDER PISTON AND EYE BOLT WERE SECURED AND SAFETIED PER MAINT MANUAL AND BOUGHT OFF BY THE INSPECTOR. LOGBOOK ENTRY WAS COMPLETED BY GATE MECH; MR XYZ. AS THIS WAS AN ACTIVE FLT; ALL WORK WAS COMPLETED AS QUICKLY AS POSSIBLE. COLLECTIVELY; ALL 3 MECHS AND THE INSPECTOR NEVER DETERMINED THAT RETRACT CYLINDER PISTON TRAVEL WAS OPPOSITE LNDG GEAR HANDLE POS. PER MAINT MANUAL PAGE XXX STATED 'CHK WHEN LEVER IS DOWN; CYLINDER POS IS EXTENDED;' ETC. WE NEVER DETERMINED THAT THE SUPPLY AND RETURN LINES WERE REVERSED. BOTH MR ZZZ AND MYSELF HAVE SUCCESSFULLY COMPLETED THIS PROC MANY TIMES IN THE PAST. FLT XXX RETURNED FROM FLT; UNABLE TO RETRACT THE R MAIN LNDG GEAR. THE FLT WAS CANCELED; THE ACFT WAS PLACED ON JACKS IN THE HANGAR; AND A GEAR SWING WAS ATTEMPTED. OUR ERROR WAS NOT CORRELATING THE POS OF THE GEAR LEVER WITH THE MOVEMENT OF THE CYLINDER. DURING THE TIME PERIOD WHEN THE ACTUATOR WAS BEING CYCLED; MR. XYZ WAS CALLED TO THE ADJOINING GATE TO DISPATCH AN OUTGOING FLT. IT IS POSSIBLE THAT THIS DISTR CONTRIBUTED TO OUR MISSING THIS CRUCIAL STEP.