COMMUTER ACFT HAS ENG COWL OPEN IN FLT. RETURN LAND.

Narrative

ON SEP/XX/94 SHORTLY AFTER TKOF WE WERE NOTIFIED BY THE FLT ATTENDANT THAT OUR R OUTBOUND ENG COWL HAD POPPED OPEN. VISUAL INSPECTION CONFIRMED THIS. WE DECLARED AN EMER AND RETURNED TO THE ARPT WITHOUT ANY PROBS. EVENTS: WE RETURNED TO STL AT XA40 AM FOR OUR LAST ROUND TRIP OF A 2-DAY TRIP WHICH HAD A SCHEDULED DEP TIME OF XB27 AM. AT APPROX XC15 AM WITH ONE PAX ON BOARD (WHEELCHAIR PAX) WE WERE NOTIFIED BY FLT OPS THAT THEY WERE SWITCHING US TO ANOTHER ACFT; SO THAT THEY COULD USE OUR ACFT FOR A FLT THAT HAD ALREADY BEEN DELAYED AND WHICH WE WERE TOLD HAD PRIORITY. I UNDERSTAND THIS TO MEAN THEY HAD MORE PAX GOING TO THE OTHER DEST THAN OUR 13 PAX. THE ACFT WE WERE SWITCHED TO WAS HAVING MAINT REPAIR AND AN ADVISE TIME OF XD30 AM. WE PREFLTED THIS ACFT AND WAITED. AT APPROX XD35 AM WE WERE NOTIFIED THAT WE WERE AGAIN BEING SWITCHED TO ANOTHER ACFT. WE DID OUR PREFLT WALKAROUND FOLLOWED BY OUR FIRST FLT OF THE DAY CHKS BECAUSE THIS ACFT HAD BEEN IN THE MAINT HANGAR FOR SCHEDULED MAINT ON SEP/XX/94. IT APPEARS THAT MAINT PERSONNEL DID NOT PROPERLY SECURE THE R OUTBOUND ENG COWL. THIS WAS NOT OBVIOUS BY VISUAL INSPECTION BY THE CAPT AND MYSELF. UNFORTUNATELY; I DID NOT TUG ON THE COWL TO CHK ITS SECURITY (SOMETHING I WILL NOW DO). I FEEL THAT AFTER WAITING OVER 3 HRS TO DEPART; HAVING TO PREFLT 3 DIFFERENT ACFT; HAVING ALREADY BEEN DELAYED FOR OVER AN HR FROM OUR SCHEDULED DEP TIME; AND SUDDENLY FEELING PRESSURED TO EXPEDITE OUR DEP HAD CONTRIBUTED TO THIS INCIDENT.