A EURO COPTER 120B STARTED THE ENGINE AND BEGAN CHECKLIST. EXPERIENCED MAIN GEARBOX LOW OIL PRESSURE WARNING. CAUSED BY PLUG FAILURE.

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PLT STARTED ENGINE; COMPLETED CHECKLIST AND THEN BEGAN TO GET REPEATED BEEPS IN HEADSET AND VISUAL WARNING ON CAUTION PANEL OF MAIN GEAR BOX 'LOW OIL PRESSURE.' PLT SHUT DOWN ENG AND OPENED COWL; TRANSMISSION FLUID WAS COVERING BOTH ENG DECK AND TRANSMISSION DECK. DISCOVERED THAT 'BLANKING' PLUG HAD COME LOOSE FROM TRANSMISSION INPUT FLANGE; CAUSING LOSS OF TRANSMISSION FLUID. THIS PROB; 'LOOSE BLANKING PLUG' IS ADDRESSED IN AMERICAN EURO COPTER 'ALERT SERVICE BULLETIN' #63-003. I THINK THIS LOOSE PLUG SHOULD BE ADDRESSED IN AN AIRWORTHINESS DIRECTIVE AS ALL THE TRANSMISSION FLUID IS LOST IN A VERY SHORT TIME; IT COULD EASILY LEAD TO A FORCED LNDG OR CRASH. WHEN THIS EVENT HAPPENS; IT IS NOT JUST A SMALL LEAK WITH MINOR CONSEQUENCES; BUT A MAJOR LEAK; EMPTYING THE TRANSMISSION WITHIN A SHORT PERIOD CAUSING A POWER REDUCTION PER THE FLT MANUAL; A RUN ON LNDG; OR POSSIBLE CRASH. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THE RPTR STATED WHEN THIS BLANKING PLUG POPS OUT; IT ONLY TAKES 45 SECONDS FOR THE MAIN GEARBOX TO INCUR A COMPLETE LOSS OF OIL. THE RPTR SAID THE RUBBER BLANKING PLUG DOES NOT SERVE ANY PURPOSE AND IS NOT REMOVED FOR ANY INSPECTION OR SHAFT ALIGNMENT. THE RPTR STATED THE MANUFACTURER HAS ISSUED A SERVICE BULLETIN DESCRIBING THE FAILURE WHEN THE PLUG HAS A LOSS OF ELASTICITY OF THE ELASTOMER AND RECOMMENDS LOCKING THE PLUG WITH A SEALING COMPOUND. THE RPTR SAID THE PROB IS A SERVICE BULLETIN MAY OR MAY NOT BE ACCOMPLISHED DEPENDING ON THE OPERATOR AND UNLIKE AN AIRWORTHINESS DIRECTIVE; WHICH IS MANDATORY AND MUST BE ACCOMPLISHED. THE RPTR STATED THE PLUG IS .75 INCHES IN DIAMETER AND IS UNDER MAIN GEARBOX OIL PRESSURE WHEN OPERATING AND IF THE BLANKING PLUG DROPS OUT; AND A LOSS OF MAIN GEARBOX OIL OCCURS; THE GEARBOX CAN BE OPERATED FOR NO MORE THAN 30 MINS. THE RPTR SAID THE PROB IS GAINING ACCESS TO THE PLUG TO CHECK FOR CONDITION AS IT CANNOT BE SEEN. THE DRIVE SHAFT ASSEMBLY MUST BE REMOVED AND THEN REINSTALLED. A TOTAL TIME OF SIX HOURS.