ATX FREIGHT TWIN EMER DOOR OPENED DURING LEVEL OFF AND THE PLT RETURNED TO LAND.

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R SIDE EMER DOOR OPENED AS ACFT ACCELERATED IN CRUISE FLT. I BELIEVE THE EMER DOOR WAS UNLATCHED OR POSSIBLE LOOSENED BY THE UNLOADING OF FREIGHT IN THE CARGO AREA. AS THE ACFT WAS ACCELERATING ABOVE 140 KIAS THE EMER DOOR OPENED AND STARTED FLAPPING VIOLENTLY. I SLOWED THE ACFT BELOW 120 KIAS WHICH STOPPED THE FLAPPING. I PROCEEDED TO TRY TO CLOSE THE EXIT BUT THE WINDOW WOULD NOT FIT BACK IN CORRECTLY AND STAY LATCHED. I INFORMED IND APCH THAT I HAD A NON EMER PROB THAT REQUIRED ME TO RETURN TO IND ARPT. LNDG WAS UNEVENTFUL. UPON EXTERIOR INSPECTION I FOUND THAT THE FIRST 3 CONNECTORS OF THE HINGE HAD SHEERED OFF; THUS WARPING THE WINDOW SO IT WOULD NOT RELATCH IN FLT. ONLY FURTHER ACTION TO POSSIBLE TAKE ON MY BEHALF WOULD HAVE BEEN TO INSPECT THE EMERGENCY EXIT PRIOR TO TKOF TO INSURE THEIR CLOSURE. THE ACFT WAS LOADED BY A FREIGHT LOADER AND THE ACFT WAS UNLOADED BY THE CAPT (ME). WHEN I WAS UNLOADING THE ACFT I DID NOT NOTICE ANYTHING UNUSUAL; NONE OF THE FREIGHT SEEMED TO CATCH OR HANG UP ON ANYTHING AND ALTHOUGH I DID NOT SPECIFICALLY CHK THE EMER EXITS; I ALSO DID NOT NOTICE ANYTHING UNUSUAL ABOUT THEM.