A B737-200 WAS DISPATCHED IN NON COMPLIANCE WITH THE L AIR CONDITIONING BAY DOOR NOT SECURED. ACFT RETURNED TO GATE WITH DAMAGED DOOR.

Narrative

ON THE MORNING OF MAR/TUE/02; MY ACFT NEEDED A 35 DEG VALVE CHANGED OUT ON THE AIR CONDITIONING SYS. DURING THE PROCESS; I OPENED BOTH L AND R AIR CONDITIONING BAY DOORS. BEFORE I HAD FINISHED MY PROJECT; A TEAM OF MECHS SHOWED UP TO TOW MY ACFT TO THE ASSIGNED GATE. I DON'T RECALL CLOSING THE AIR CONDITIONING BAY DOORS; BECAUSE I HAD TO GATHER UP MY TOOLS AND RUSH TO THE LINE. THE AIR CONDITIONING SYS STILL HAD ICE IN THE AIR CYCLE MACHINE AND IT WAS STILL INOP. WHEN I ARRIVED AT THE ACFT; BOTH DOORS LOOKED LIKE THEY WERE UP AND SECURED. I REOPENED THE R BAY DOOR; PUT SOME HEAT ON THE SYS FOR ABOUT 10 MINS. AFTER OPS CHKING THE SYS; I CLOSED THE BAY DOOR AND LOADED UP MY TOOLS AND DROVE BACK TO THE OFFICE TO SIGN THE LOGBOOK. THE PRE-DEP CHK WAS ASSIGNED TO ME. THEREFORE; I GRABBED THE LOGBOOK AND TOOK IT TO THE ACFT. I DID AN EXTERIOR WALK OF THE ACFT; CHKED OIL CAPS AND GAVE THE LOG BACK TO PLTS. THE ACFT PUSHED BACK FOR FLT 15 MINS LATER; AFTER GIVING THE PLTS THE LOGBOOK. EVEN THOUGH SOMEONE ELSE CLOSED THE DOOR; I FAILED TO DETECT THAT IT WAS NOT SECURED ALL THE WAY. THE ACFT LEFT ON ITS FLT; AND AT 12000 FT AND FLYING AT 280 KTS; THE PLTS HEARD A THUMP AND THEN NOISE; PROBABLY AIR RUSHING PAST THE DAMAGED BAY DOOR. THE PLTS RETURNED TO ZZZ AND DISCOVERED DAMAGE TO THE L-HAND AIR CONDITIONING BAY DOOR. I BELIEVE SOME OF THE LEADING EDGE LATCHES WERE IMPROPERLY SECURED. MY FAULT.