DC8 CARGO ACFT HAD THE CARGO DOOR COME OPEN ON CLBOUT.

Narrative

THE FLT WAS SCHEDULED TO DEPART ILN AT XA40; HOWEVER; DUE TO THE PREVAILING WX CONDITIONS; ICE AND SNOW; WE WERE DELAYED FOR APPROX 3.5 HRS. THE FLT BLOCKED OUT AT XD26 AND WE WERE OFF AT XD43. WE WERE CLRED TO 8000 FT AND TURNED OVER TO CVG APCH TO CONTINUE OUR CLB. IN THE MEANTIME THE FE WAS RUNNING THE AFTER TKOF CHKLIST AND STARTING THE CABIN TURBO COMPRESSOR. WHEN THE FE TURNED ON THE LAST CABIN TURBO COMPRESSOR; WE NOTICED A RUSH OF AIR FOLLOWED BY A PRESSURE BUMP. WITHIN A FEW SECONDS WE RECEIVED A MASTER WARNING FOLLOWED BY CABIN DOOR AND CARGO DOOR RED LIGHTS ON THE FE'S PANEL. I THEN INSTRUCTED THE FE TO DEPRESSURIZE THE ACFT AND CHK THE DOOR FROM A DISTANCE IN ACCORDANCE WITH THE ACFT'S ABNORMAL PROC. HE RETURNED AND INFORMED ME THAT IT APPEARED THAT THE DOOR WAS LOCKED. BASED ON THE INDICATIONS WE RECEIVED AFTER WE TURNED ON THE LAST CABIN TURBO COMPRESSOR; IE; PRESSURE BUMP AND RUSH OF AIR; I DECIDED THAT THE MOST PRUDENT THING TO DO WAS TO RETURN TO ILN AS INDICATED IN THE ABNORMAL. I THEN INSTRUCTED THE FE TO PROCEED WITH THE FUEL DUMP CHKLIST WHILE I RECEIVED CLRNC TO A DUMPING AREA. WE THEN ACCOMPLISHED ALL THE ITEMS NEEDED TO RETURN AND MADE AN UNEVENTFUL LNDG BACK AT ILN. THE FACTORS THAT PLAYED A ROLE IN FORMULATING MY DECISION TO RETURN WERE THE INITIAL INDICATIONS WE RECEIVED COUPLED WITH ICING CONDITIONS AND A RECENT MEMO ADDRESSING CARGO DOORS; WHICH PERTAINED TO OUR ACFT. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THE DC8-61 ACFT HAS BEEN RETROFITTED WITH A PARTICULAR CARGO DOOR. THE CAPT INDICATED THAT THERE IS AN FAA AIRWORTHINESS DIRECTIVE NOTE ON THE DOOR. THIS ACFT WAS IN COMPLIANCE WITH THE AIRWORTHINESS DIRECTIVE. THE ACFT HAD A SIMILAR CARGO DOOR DISCREPANCY SEVERAL FLTS BEFORE. THE VERY NEXT FLT A SIMILAR INCIDENT OCCURRED. ON THIS FLT; MAINT FOUND BOTH SYS A AND B LIMIT SWITCHES BENT AND BROKEN. EVEN THOUGH REPAIRED; THE CARGO DOOR HAD A REPEAT DISCREPANCY ON THE NEXT FLT. THE CAPT KNOWS OF 3 OTHER DOOR INCIDENTS BESIDES THE ONES ON THIS ACFT. THE CAPT SAID THAT THE ACR IS CRITICIZING CREWS FOR NOT FLYING THE ACFT IN THIS CONFIGN. THE CREWS BEFORE AND AFTER THIS INCIDENT CONTINUED THE FLT TO ITS DEST.