OPEN CARGO DOOR IN FLT.

Narrative

WE WERE ON A QUICK TURN IN NEW HAVEN; CT; WHERE WE WERE DROPPING OFF PAX AND PICKING UP SOME MORE. THE CAPT LEFT THE AIRPLANE TO GET THE LUNCHES FOR THE PAX WHICH WAS IN THE OUTSIDE REAR BAGGAGE COMPARTMENT. WHILE IN THAT PROCESS; HE WAS DISTR BY THE DISEMBARKING PAX DRIVING TOO CLOSE THE ACFT; SO HE WENT TO SEE WHAT HE WANTED. RESOLVING THAT PROB; HE CONTINUED GETTING THE PLANE READY FOR THE NEXT GROUP OF PAX. OUR EMBARKING PAX ARRIVED AND WE WERE READY TO LEAVE. RIGHT AFTER TKOF WE FELT AND HEARD A VIBRATION AND THOUGHT IT WAS A STARTER/GENERATOR BEARING (WE'VE HAD THIS PROB BEFORE). WE DECIDED TO BRING THE PLANE BACK AND LAND. AFTER LNDG; IT WAS DISCOVERED THAT THE REAR BAGGAGE DOOR WAS OPEN. WE ARE NOT SURE IF IT WAS OPEN ALL THE TIME OR HAD COME OPEN IN FLT. IN DOING A POST FLT WE FOUND OUT THAT THE WARNING LIGHT SWITCH THAT SHOULD HAVE TOLD US THAT THE DOOR WAS NOT CLOSED WAS INOP AND DID NOT GIVE US A DOOR OPEN/UNLOCKED LIGHT. AFTER A PROPER PREFLT AND VERIFYING THAT THE DOOR WAS CLOSED; WE CONTINUED THE TRIP WITH NO FURTHER PROB. A PROPER PREFLT WALK AROUND PROBABLY WOULD HAVE PREVENTED THIS FROM HAPPENING. ALSO; WHEN THE DOOR CAME OPEN; WE LOST OUR ENG COVERS IN FLT. FORTUNATELY NOTHING OR NO ONE WAS HURT OR DAMAGED ON THE GND.