ACR CAPT RPTS ABNORMAL PREFLT OF CREW OXYGEN MASK IN MD80.

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WHILE PREFLTING THE PLT'S OXYGEN SYS I NOTICED A TEST DISCREPANCY. I PUT THE CAPT'S OXYGEN MASK ON AND WITH THE REGULATOR IN NORMAL/100%/ON I HAD NORMAL MASK OP. I THEN WENT TO MASK TEST TO CHK FOR MASK SEAL WITH POSITIVE PRESSURE AND HAD A NORMAL TEST. THE LAST STEP OF MY PREFLT IS TO TURN THE REGULATOR OFF TO TEST FOR NO AIR/OXYGEN FLOW. THE MASK/REGULATOR INITIALLY HAD NO FLOW; BUT THEN I COULD BREATHE AMBIENT AIR THROUGH THE MASK. I HAD NO OXYGEN BLINKER. THE FO HAD THE SAME PROB WITH HIS MASK/REGULATOR. MAINT REPLACED BOTH PLTS MASKS; BUT WE HAD THE SAME PROB. MAINT THEN REPLACED BOTH REGULATORS; BUT WE STILL HAD THE SAME PROB. THIS WAS THE WAY I WAS TAUGHT TO TEST A MASK BACK IN MY MIL DAYS; THIS WAS HOW I WAS TAUGHT TO TEST A MASK WHEN I WAS A B727 FE; AND THIS WAS HOW I WAS TAUGHT TO TEST THE MASK WHEN I CHKED OUT ON THE MD80 IN 1994. I CHKED THE PROCS AND IT DOES NOT SAY TO TEST THE MASK/REGULATOR IN THE OFF POS; BUT AS I SAID THIS WAS HOW I WAS TRAINED; AND THIS WAS HOW EVERY MD80 I HAVE PREFLTED HAS WORKED. MAINT SAID THAT THERE WAS NOTHING ELSE TO CHANGE AND THAT THE MAINT CHKLIST SHOWED IT WAS AIRWORTHY BECAUSE NO OXYGEN FLOWED WITH THE REGULATOR OFF. THE FO; MYSELF; AND A MAINT TECHNICIAN WENT TO 3 OTHER ACFT AND TESTED 6 MASK REGULATORS. 5 OF THE 6 TESTED WITH NO AIR/OXYGEN FLOW WHEN THE REGULATOR WAS IN 100% OFF; AS I HAD BEEN TAUGHT. ONE OF THE MASK/REGULATORS ALLOWED AMBIENT AIR IN AS IN OUR ACFT. I CALLED THE DUTY MGR AND ASKED FOR AN MD80 GUY TO GET SOME GUIDANCE ON WHICH WAY THE SYS NEEDED TO WORK. I TALKED TO THE MD80 FLT MGR AND WAS TOLD THAT I WAS DOING TOO MUCH PREFLT ON THE MASK. MY CELL PHONE DROPPED THE CALL AT THIS POINT. I THEN CALLED UNION SAFETY REPRESENTATIVE TO SEE IF THE SYS WAS SAFE TO FLY. MY CONCERN AT THIS POINT WAS THAT IF WE HAD A SMOKE IN THE COCKPIT SITUATION WE COULD GET AMBIENT COCKPIT AIR MIXED WITH 100% OXYGEN. UNION SAFETY REPRESENTATIVE CALLED ACR SAFETY REPRESENTATIVE AND WE DISCUSSED WHAT WOULD BE IN THE BEST INTEREST OF SAFETY. WE DECIDED THAT IF THE SYS WAS FAULTY AND IF WE HAD SMOKE IN THE COCKPIT; THE OXYGEN UNDER PRESSURE WOULD BLOCK OUT ANY DANGEROUS SMOKE SO WE WOULD BE SAFE. CLARIFICATION ON THE MASK/REGULATOR PREFLT PROCS WOULD BE HELPFUL. ACR AND MANUFACTURER SHOULD SPECIFY HOW THE MASKS ARE SUPPOSED TO WORK WITH THE REGULATOR TURNED OFF; AND FIND OUT WHY ACFT TESTED DIFFERENTLY. DOES ACR MD80 FLEET HAVE A MASK REGULATOR PROB; OR IS MY PREFLT IN ERROR. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: RPTR INDICATES HE WAS COUNSELED BY ACR FLT MGR THAT SINCE THE TEST IN QUESTION THAT THE MASKS FAILED IS NOT PART OF THE APPROVED FLT MANUAL PROC; HE SHOULD DISCONTINUE USING THAT TEST PROC.