ACR MLG RETURN LNDG AFTER GEAR DOOR NOT LOCKED IN UP POS. RPTR COMPLAINT REF NO CHKLIST USE ITEM EVEN THOUGH EICAS ALERT ON DOOR.

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AT GEAR RETRACTION WE RECEIVED MULTIPLE AURAL AND VISUAL ALERTS. #1 ON MFDU SCREEN WAS 'L LNDG GEAR DOOR LOCK SWITCH.' 'SPD LIMIT' WAS ON PFD SPD SCALE. ALSO ON MFDU SCREEN: 'AFCAS MODE; NO ALAND; AFCAS MAINT REQ.' I ASKED FO TO GET PLTS HANDBOOK OUT FOR ABNORMAL PROCS (LNDG GEAR). NEITHER OF US COULD FIND ANY PROC FOR 'L LNDG GEAR DOOR LOCK SWITCH.' I CYCLED THE GEAR TO DOWN AND HAD SAME DOOR LOCK SWITCH WARNING WITH 3 GREEN (DOWN AND LOCKED). CYCLED GEAR BACK UP AND SAME WARNINGS APPEARED; SO I ELECTED TO RETURN TO THE ARPT. ADVISED FLT ATTENDANTS AND PAX OF GEAR DOOR PROB; CALLED COMPANY FOR A GATE AND MAINT. ASKED DEP TO SEQUENCE US FOR RETURN LNDG; NO EQUIP NECESSARY. PRIOR TO LNDG ASKED TWR AND AN ACFT ON GND FOR VISUAL ON DOOR AND THEY SAID IT APPEARED UP. NORMAL LNDG FOLLOWED AND AFTER TURNOFF AT HIGH SPD AND STOPPING; ACFT AGAIN ASKED TAXIING ACFT FOR A VISUAL ON THE DOOR; IF CLOSED. AFTER RECEIVING AFFIRMATIVE ANSWER; TAXIED TO GATE WHERE MAINT FOUND AND REPAIRED BROKEN DOOR LOCK SPRING. MY PROB WITH THIS SIT IS THAT IF YOU CAN GET AN ALERT ON THE SCREEN THERE SHOULD BE A PROC IN THE BOOK TO COVER IT.