AN MD11 AFTER TKOF DECLARED AN EMER AND RETURNED TO THE FIELD DUE TO UNABLE TO RETRACT THE NOSE LNDG GEAR CAUSED BY A GEAR LOCK PIN INSTALLED.

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ON AUG/XA/99; ACR MD11 ACFT XYZ RETURNED TO THE GATE AFTER DEPARTING ZZZ FOR CVG. IT WAS FOUND THAT THE NOSE GEAR PIN WAS STILL INSTALLED; WHICH DID NOT ALLOW THE NOSE GEAR TO RETRACT. BEFORE DEP; I HAD BEEN ASSISTING WITH A HYD LINE REPLACEMENT IN THE R-HAND WHEEL WELL. UPON COMPLETION OF THE REPLACEMENT I REMOVED THE MAIN LNDG GEAR PINS THEN PROCEEDED TO REMOVE WHAT I THOUGHT WAS THE NOSE GEAR PIN. IN FACT; WHAT I REMOVED WAS THE STEERING BYPASS PIN. WHEN I STOWED 3 PINS IN THE POUCH IN THE COCKPIT I HAD EVERY CONFIDENCE AND BELIEF THAT I HAD REMOVED GEAR PINS FROM ALL 3 GEAR LEGS. WHEN THE ACFT RETURNED IT WAS NOTED THAT THE STREAMER FROM THE NOSE GEAR PIN WAS NOT HANGING DOWN. I WAS RUSHING TO GET THE ACFT OUT BEFORE THE PLTS RAN OUT OF TIME AND IN RETROSPECT SHOULD HAVE LOOKED CLOSER WHEN I REMOVED THE PIN. OTHER FACTOR: DO NOT HAVE MUCH EXPERIENCE ON MD11. SUPPLEMENTAL INFO FROM ACN 446008: DURING PUSHBACK; A SHEAR PIN WAS BROKE ON THE TOW BAR DUE TO THE FACT THERE WAS NO BYPASS PIN INSTALLED. IT WAS NOT REALIZED UNTIL THE ACFT HAD DEPARTED THAT ABC HAD MISTAKEN THE BYPASS PIN FOR THE DOWNLOCK PIN.