Narrative:

While doing a service check; I noted that crew oxygen required servicing. I serviced the oxygen per the MM supplement. After servicing I checked the system pressure and flow in the flight deck. I had good flow and what I thought was a proper pressure drop. Later the flight crew reported low pressure when testing the mask. I had already left for the day so another technician was sent to investigate. He reported finding the valve not fully open and stiff. When I came in to work next; my manager was waiting to talk to me. I was surprised to learn that there had been a problem with my servicing the other day. In the course of trying to determine what went wrong my manger discovered that I had not received oxygen servicing issue training. I subsequently received this training. In the course of this training I learned of the possibility of a false fully open feeling when opening the valve; which can result in leaving a valve partially open. I also was shown the difference in pressure drop of a fully open valve to a partially open valve. The stiffness of the partially open valve led me to believe that the valve was fully open. I was unaware of the difference in pressure drop between a fully open valve and a partially open valve.callback conversation with reporter revealed the following information: reporter stated his B737-800 aircraft do not have an external fill port to service the crew oxygen bottle. As a result; the crew oxygen bottles are removed; serviced or exchanged and reinstalled in the aircraft and a log book service entry is made. His company uses steel or carbon fibre composite bottles in their aircraft. His report involves a composite oxygen bottle and the problem with the round wheel type handle that has nubs on it and the sudden stiff spot when trying to open the valve. This type of handle does not allow any frame of reference when trying to count handle rotations while opening the valve. This becomes even more important with the composite bottle because of the tendency of the composite valve handle to suddenly stiffen up and feel as if the valve is full open. Normal full open is 4 to 4.5 turns of the handle to reach full open. These composite bottles are locking-up at only three turns. Although the initial oxygen mask flow checks appear good and within less than 100 pounds pressure drop (supply); these same masks will later not have adequate oxygen supply. Normally; servicing of crew oxygen bottles is required every few days due to the flight crews' preflight masks checks with the servicing sign-offs in the log books. However; since his company has taken a more threatening position against anyone involved in these composite bottle valve problems and resultant low oxygen flow crew write-ups; maintenance has seen a dramatic drop-off of maintenance entries in the log books even though servicing requirements are still being met. Mechanics are now worried the last one to sign off a log book for servicing crew oxygen may not in actuality be the last one to have serviced the crew bottle.

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Original NASA ASRS Text

Title: A B737-800 ACFT MECH RPTS A CREW COMPOSITE OXYGEN BOTTLE HANDLE THAT WAS FOUND NOT FULLY OPENED AFTER THE BOTTLE WAS SERVICED. THE RPTR STATES THAT THE HANDLE FEELS AS IF IT IS FULLY OPEN; BUT IT IS NOT.

Narrative: WHILE DOING A SVC CHK; I NOTED THAT CREW OXYGEN REQUIRED SERVICING. I SERVICED THE OXYGEN PER THE MM SUPPLEMENT. AFTER SERVICING I CHKED THE SYSTEM PRESSURE AND FLOW IN THE FLT DECK. I HAD GOOD FLOW AND WHAT I THOUGHT WAS A PROPER PRESSURE DROP. LATER THE FLT CREW RPTED LOW PRESSURE WHEN TESTING THE MASK. I HAD ALREADY LEFT FOR THE DAY SO ANOTHER TECHNICIAN WAS SENT TO INVESTIGATE. HE RPTED FINDING THE VALVE NOT FULLY OPEN AND STIFF. WHEN I CAME IN TO WORK NEXT; MY MANAGER WAS WAITING TO TALK TO ME. I WAS SURPRISED TO LEARN THAT THERE HAD BEEN A PROB WITH MY SERVICING THE OTHER DAY. IN THE COURSE OF TRYING TO DETERMINE WHAT WENT WRONG MY MANGER DISCOVERED THAT I HAD NOT RECEIVED OXYGEN SERVICING ISSUE TRAINING. I SUBSEQUENTLY RECEIVED THIS TRAINING. IN THE COURSE OF THIS TRAINING I LEARNED OF THE POSSIBILITY OF A FALSE FULLY OPEN FEELING WHEN OPENING THE VALVE; WHICH CAN RESULT IN LEAVING A VALVE PARTIALLY OPEN. I ALSO WAS SHOWN THE DIFFERENCE IN PRESSURE DROP OF A FULLY OPEN VALVE TO A PARTIALLY OPEN VALVE. THE STIFFNESS OF THE PARTIALLY OPEN VALVE LED ME TO BELIEVE THAT THE VALVE WAS FULLY OPEN. I WAS UNAWARE OF THE DIFFERENCE IN PRESSURE DROP BETWEEN A FULLY OPEN VALVE AND A PARTIALLY OPEN VALVE.CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: RPTR STATED HIS B737-800 ACFT DO NOT HAVE AN EXTERNAL FILL PORT TO SERVICE THE CREW OXYGEN BOTTLE. AS A RESULT; THE CREW OXYGEN BOTTLES ARE REMOVED; SERVICED OR EXCHANGED AND REINSTALLED IN THE ACFT AND A LOG BOOK SERVICE ENTRY IS MADE. HIS COMPANY USES STEEL OR CARBON FIBRE COMPOSITE BOTTLES IN THEIR ACFT. HIS RPT INVOLVES A COMPOSITE OXYGEN BOTTLE AND THE PROBLEM WITH THE ROUND WHEEL TYPE HANDLE THAT HAS NUBS ON IT AND THE SUDDEN STIFF SPOT WHEN TRYING TO OPEN THE VALVE. THIS TYPE OF HANDLE DOES NOT ALLOW ANY FRAME OF REFERENCE WHEN TRYING TO COUNT HANDLE ROTATIONS WHILE OPENING THE VALVE. THIS BECOMES EVEN MORE IMPORTANT WITH THE COMPOSITE BOTTLE BECAUSE OF THE TENDENCY OF THE COMPOSITE VALVE HANDLE TO SUDDENLY STIFFEN UP AND FEEL AS IF THE VALVE IS FULL OPEN. NORMAL FULL OPEN IS 4 TO 4.5 TURNS OF THE HANDLE TO REACH FULL OPEN. THESE COMPOSITE BOTTLES ARE LOCKING-UP AT ONLY THREE TURNS. ALTHOUGH THE INITIAL OXYGEN MASK FLOW CHECKS APPEAR GOOD AND WITHIN LESS THAN 100 POUNDS PRESSURE DROP (SUPPLY); THESE SAME MASKS WILL LATER NOT HAVE ADEQUATE OXYGEN SUPPLY. NORMALLY; SERVICING OF CREW OXYGEN BOTTLES IS REQUIRED EVERY FEW DAYS DUE TO THE FLT CREWS' PREFLIGHT MASKS CHKS WITH THE SERVICING SIGN-OFFS IN THE LOG BOOKS. HOWEVER; SINCE HIS COMPANY HAS TAKEN A MORE THREATENING POSITION AGAINST ANYONE INVOLVED IN THESE COMPOSITE BOTTLE VALVE PROBLEMS AND RESULTANT LOW OXYGEN FLOW CREW WRITE-UPS; MAINT HAS SEEN A DRAMATIC DROP-OFF OF MAINT ENTRIES IN THE LOG BOOKS EVEN THOUGH SERVICING REQUIREMENTS ARE STILL BEING MET. MECHANICS ARE NOW WORRIED THE LAST ONE TO SIGN OFF A LOG BOOK FOR SERVICING CREW OXYGEN MAY NOT IN ACTUALITY BE THE LAST ONE TO HAVE SERVICED THE CREW BOTTLE.

Data retrieved from NASA's ASRS site as of January 2009 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.