What was found
AFTER TAKEOFF, THE FLIGHT CREW NOTICED AIRFRAME VIBRATION. ACFT LANDED AT THE CLOSEST AIRPORT WITHOUT INCIDENT. A VISUAL INSPECTION OF THE RT COWLING SHOWED THAT THE FWD OTBD 2 LATCHES WERE UNLATCHED AND THE AFT OTBD LATCH WAS SECURED. THE UPPER AND LOWER COWLING SUSTAINED MINOR DAMAGE. CAUSE WAS A FAILURE TO SECURE THE TWO FWD LATCHES AFTER CHECKING ENGINE OIL. PROCEDURES FOR ENSUING A THOROUGH PREFLIGHT INSPECTION SHOULD BE REINFORCED AND ALL PERSONNEL SHOULD FOLLOW A COMPLETE PREFLIGHT INSPECTION AFTER THE ACFT HAS BEEN DISTURBED FOR ANY REASON PRIOR TO FLIGHT. (K)