A SAAB 340A WAS DISPATCHED IN NON COMPLIANCE WITH THE R ENG OUTBOARD COWLING NOT LATCHED CLOSED.

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DEPARTED ZZZ FOR WWW. AFTER 1 MINUTE AND 30 SECONDS; FLT ATTENDANT NOTIFIED US THAT A COWLING ON THE R ENG APPEARED LOOSE. WE HAD A DEAD HEADING CREW MEMBER LOOK AT COWLING AND HE CONFIRMED THAT IT APPEARED LOOSE. WE RETURNED TO ZZZ WITHOUT INCIDENT. MAINT HAD PREVIOUSLY DONE AN OIL INSPECTION ON BOTH ENGS; BUT THEY CONFIRMED THAT ALL LATCHES WERE CLOSED AND SECURE. THE SAME AS THE FO HAD CONFIRMED DURING HIS PREFLT. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: RPTR STATED THE ACFT WAS A SAAB 340A. THE ENG COWLING LATCHES ON THIS AIRPLANE CAN BE FALSE LATCHED AND THE PUSH BUTTONS CAN BE FLUSH WITH THE COWLING SURFACE AND STILL BE UNLOCKED. THE RPTR SAID IT IS HIS BELIEF THAT THE COWLING WAS OPENED AFTER THE TECHNICIAN OILED THE ENG AND THE FO MADE THE WALK AROUND PREFLT INSPECTION. CALLBACK CONVERSATION WITH RPTR ACN 461750 REVEALED THE FOLLOWING INFO: THE RPTR STATED THAT WHEN THE ACFT RETURNED; THE #2 ENG OUTBOARD COWLING FORWARD LATCH WAS FOUND UNLOCKED AND THE AFT LATCH WAS LOCKED. THE RPTR STATED THIS COWLING UNLATCH PROB HAS HAPPENED BEFORE; BUT FORTUNATELY NOT INVOLVING THE RPTR. THE RPTR SAID THE COMBINATION OF OLD WORN LATCHES AND REALLY BEAT UP COWLING MAKES COWLING LATCHING CRITICAL. THE RPTR SAID THERE IS NO VISUAL INDICATION THE COWLING IS LATCHED AS THE PUSH BUTTONS ON THE LATCHES ARE FLUSH WHEN LOCKED OR UNLOCKED.