BE36 PLT HAD THE L SIDE ENG COWL COME OPEN ON DSCNT.

Narrative

PLT SIDE ENG COWLING WAS SECURED PRIOR TO FLT AFTER THE ENG COMPARTMENT WAS INSPECTED AND 1 QUART OF OIL WAS ADDED. THE ENG COWL SECURING MECHANISM WAS LATCHED AND THE COWL WAS INSPECTED AND TESTED FOR SECURITY AS IS MY NORMAL ROUTINE. ON A DIRECT FLT FROM MUNCIE; IN; NO ABNORMALITIES WERE NOTED. THE COWLING APPEARED INTACT DURING AN ENRTE LEG OF APPROX 65 NM. AFTER ESTABLISHING CONTACT WITH CINCINNATI APCH CTL; I WAS ASKED TO DSND OUT OF 5500 FT MSL TO 3500 FT MSL OR LOWER. SHORTLY AFTER PITCHING THE NOSE OF THE ACFT DOWN; THE PLT SIDE ENG COWL FLEW OPEN. BEING OVER HAMILTON ARPT; THE ACFT WAS IMMEDIATELY LANDED AND INSPECTED FOR DAMAGE. THE COWLING DID NOT SEPARATE IN MIDAIR NOR WERE THERE ANY ABNORMAL HANDLING CHARACTERISTICS TO THE ACFT. AFTER LNDG; IT WAS NOTED THAT THE FORWARD LATCHING PIN WAS STILL INTACT WITH THE COWL DOOR; BUT THE AFT LATCHING MECHANISM HAD COMPLETELY SEPARATED FROM ITS NORMAL ATTACHMENT ALONG THE LOWER ENG COWL. I FELT THAT THERE WAS A FAILURE OF THE COWL LATCHING MECHANISM. I AM UNSURE OF WHAT FURTHER ACTIONS COULD HAVE BEEN PERFORMED DURING PREFLT BEYOND LOOKING CLOSELY AT THE LATCHING MECHANISM FOR ANY OBVIOUS SIGNS OF IMMINENT FAILURE. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THE ACFT WAS A RENTAL ACFT FROM A FLT SCHOOL. THE PLT ADMITTED HE DID NOT PULL UP ON THE TAB; TO INSURE THE COWL WAS LATCHED. THE PLT DID NOT TELL ANYONE ABOUT THE INCIDENT. AFTER LNDG; THE PLT RELATCHED THE COWLING; THEN FLEW WITHOUT A PROB.