A CRJ200 ON THE SECOND FLT LEG HAD THE LOWER COWL OF THE L ENG DEPART THE ACFT.

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COLD RUSHED TO GET THE PLANE AT GATE. PANEL TIGHT TO INSTALL APPEARED SECURE AND PASSED TWO PLT'S INSPECTIONS. ON SECOND FLT TO ZZZ THE COWL DOOR DEPARTED FROM THE ACFT.CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THE RPTR STATES THE FASTENERS WERE INSTALLED AND TESTED PER THE PROCS AND WERE INSPECTED PER THE CHK DOCUMENTS PRIOR TO THE GATE DELIVERY; AND THE COWL PANELS WERE AGAIN VISUALLY CHKED AT THE GATE BY THE DELIVERING TECH AND THE FO. THE RPTR INDICATED THAT PRIOR TO THE SECOND LEG FLT; THE FO VISUALLY CHKED THE COWLING AND FOUND NO LOOSE OR MISSING FASTENERS; AND ON THE SECOND LEG FLT; THE L LOWER COWLING DEPARTED THE ACFT. THE RPTR BELIEVES THE CAMLOCKS WERE WORN AND VIBRATED LOOSE. THE RPTR INDICATED THAT THIS IS NOT THE FIRST FAILURE OF THESE FASTENERS AS ONE COWLING HAS PREVIOUSLY BEEN RPTED AS DEPARTING THE ACFT. RPTR NOTED FREQUENT RPTS BY CREWS OF MISSING OR LOOSE FASTENERS ARE PROOF THESE WORN FASTENERS ARE NOT BEING FOUND AND REPLACED ON A ROUTINE BASIS.