EMER DECLARED IN A RETURN LAND INCIDENT.

Narrative

AFTER A THOROUGH PREFLT WE DEPARTED DFW ENRTE TO CLL. THE CAPT WAS FLYING AND I WAS THE PNF. AFTER COMPLETING THE AFTER TKOF CHKLIST; THE CAPT NOTED TO ME THAT THE PLANE WAS NOT PERFORMING NORMALLY. WE THEN HEARD NOISE FROM THE L ENG AND SAW THAT THE COWLING WAS COMING LOOSE. HE SLOWED THE ACFT; WE DECLARED AN EMER AND RETURNED TO LAND AT DFW WITHOUT FURTHER INCIDENT. I THINK THE PROB WAS CAUSED BY WORN FASTENERS ON THE ENG COWLING AND THIS PROB COULD HAVE BEEN AVOIDED WITH USING NEWER EQUIP THAN THAT OF THE EMB-100. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: AFTER THE ACFT HAD RETURNED TO DFW; THE FIRST QUESTION THE MECHS ASKED THE FO WAS; 'DID YOU CHK THE COWLING ON THE PREFLT?' THE ANSWER WAS; 'OF COURSE I DID.' THE RPTR STATED THAT A NEW COWLING WAS REQUIRED; SO HE DID NOT STAY AROUND FOR THE INSTALLATION OF THAT. THE NEXT DAY; HE TALKED TO THE CREW WHO HAD FLOWN THE SAME ACFT AND THEY TOLD HIM THAT; AFTER ARRIVING AT THEIR DEST ARPT; 1 OF THE 6 FASTENERS HAD COME LOOSE. THE FASTENERS ARE THE SNAP-TO-FLUSH-CLOSE POS TYPE. VERY HARD TO MISS BEING OPEN ON A PREFLT. RPTR BLAMES INCIDENT ON ACFT AGE; ACFT BEING AN EMB-110.