AN ACR LTT HAD TO RETURN LAND BECAUSE OF A VIBRATION.

Narrative

FO'S ATTITUDE HDG REF SYS HAD BEEN WORKING INTERMITTENTLY ON PREVIOUS FLT. MAINT WAS NOTIFIED. PRIOR TO DEP; FO CONDUCTED TURNAROUND PREFLT; INCLUDING NOSE GEAR DOORS WHICH MAINT HAD OPENED TO GAIN ACCESS TO THE AVIONICS COMPARTMENT. ALL DOORS APPEARED TO BE CLOSED AND LOCKED. VIBRATION DEVELOPED AFTER GEAR RETRACTION. SINCE THE VIBRATION WOULD STOP AFTER LOWERING THE GEAR; CREW SUSPECTED A GEAR DOOR WOULD NOT FULLY CLOSE. AS A SAFETY PRECAUTION; CREW ELECTED TO RETURN TO CVG AND HAVE MAINT INVESTIGATE. AFTER LNDG; INSPECTION FOUND L NOSE GEAR DOOR OPEN. PRIOR TO RELATCHING; THE DOOR WAS PLACED IN THE CLOSED POS; AND IT STAYED IN THE CLOSED POS. EMPHASIS MUST BE PLACED ON PREFLT ACTIVITIES; WHETHER IT BE ACFT ACCEPTANCE OR TURNAROUND. CAREFUL ATTN TO DOORS CANNOT BE OVERLOOKED. WHILE THE NOSE GEAR DOOR APPEARED CLOSED; ONLY PULLING DOWN WOULD VERIFY IT WAS FULLY CLOSED AND LATCHED. SUPPLEMENTAL INFO FROM ACN 252660: THE TWR SUPVR MADE THE DECISION TO ROLL THE CRASH EQUIP. WHEN MAINT GOT TO THE ACFT; THE L NOSEWHEEL DOOR WAS OPEN. THE LATCH WAS CLOSED. INSPECTION REVEALED NOTHING BROKEN. THE DOOR COULD BE CLOSED AND THE LATCH CLOSED; AND NOT BE ENGAGED. THE DOOR WOULD STAY IN THE CLOSED POS; EVEN THOUGH NOT LATCHED.