LOSS OF CABIN PRESSURE DUE TO AN IMPROPERLY CLOSED DOOR CAUSES LGT TO RETURN LAND.

Narrative

TOOK OFF MSP; ACFT WOULD NOT PRESSURIZE. RETURNED TO MSP. MECH FOUND AFT L CABIN SVC DOOR CLOSED IMPROPERLY. TOP LATCHES SEATED GIVING DOOR CLOSED INDICATION IN COCKPIT. BOTTOM LATCHES SEATED INSIDE OF DOOR FRAME ALLOWED BOTTOM OF DOOR TO REMAIN OPEN APPROX 1 INCH. CATERER HAD CLOSED DOOR IMPROPERLY. INCIDENT ATTRIBUTED TO CATERER NOT CHKING DOOR PROPERLY (CATERING TRUCK STILL IN PLACE AT DOOR DURING SO WALKAROUND). ALSO; THE DESIGN OF THE DOORS ON LGT ACFT ALLOWS A DOOR TO REMAIN 'OPEN' WITH DOOR CLOSED INDICATION. SUPPLEMENTAL INFO FROM ACN 252268: THE DOOR LIGHTS WERE OUT AND TESTED GOOD. FROM THE INSIDE THE DOOR APPEARED TO BE CLOSED PROPERLY. TO PREVENT THIS FROM HAPPENING AGAIN: 1) WE SHOULD DO THE WALKAROUNDS AFTER CATERING HAS FINISHED; AND CLOSED THE DOORS; AND 2) CATERING PERSONNEL SHOULD HAVE MORE TRAINING TO MAKE SURE THE DOORS ARE SECURE. SUPPLEMENTAL INFO FROM ACN 251864: CONSIDERATION SHOULD BE GIVEN TO REQUIRING AN ADDITIONAL INSPECTION BY MAINT ON THE COCKPIT AFTER CATERING.