Narrative:

I opened up a company message yesterday regarding a B737-800 aircraft. It was found that the flight deck O2 valve in the east/east compartment was not fully open. The company email implies that a number of flight crews did properly check their O2 system by noticing a dip in the flight deck O2 gauge. I conduct all flight deck O2 checks in the same manner on every aircraft I am flying (per our flight handbook procedures). I did not see any O2 pressure change on aircraft on the day in question.callback conversation with reporter revealed the following information: reporter stated that the valve handle of the O2 bottle involved was only open 3 turns instead of the full 6 turns prescribed in the maintenance manual. This valve position still allowed full O2 flow but did not meet the preflight requirements. The valve position is a maintenance function because the bottle and valve are located in the east and east compartment; inaccessible to the flight crew. However; the reporter's air carrier expects the flight crew to observe the O2 bottle pressure for a pressure drop during O2 mask checking. However; unless the bottle valve is nearly closed; the reporter stated that there is never a drop in pressure during the check; therefore the flight crew has absolutely no way of knowing if the valve is fully or partially open.

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Original NASA ASRS Text

Title: A B737-800 PILOT COMMENTS THAT THE CREW OXYGEN SYSTEM APPEARED NORMAL ALTHOUGH THE ACR REPORTED THE BOTTLE VALVE NOT FULLY OPEN DURING PREFLT.

Narrative: I OPENED UP A COMPANY MESSAGE YESTERDAY REGARDING A B737-800 AIRCRAFT. IT WAS FOUND THAT THE FLIGHT DECK O2 VALVE IN THE E/E COMPARTMENT WAS NOT FULLY OPEN. THE COMPANY EMAIL IMPLIES THAT A NUMBER OF FLIGHT CREWS DID PROPERLY CHECK THEIR O2 SYSTEM BY NOTICING A DIP IN THE FLIGHT DECK O2 GAUGE. I CONDUCT ALL FLIGHT DECK O2 CHECKS IN THE SAME MANNER ON EVERY AIRCRAFT I AM FLYING (PER OUR FLIGHT HANDBOOK PROCEDURES). I DID NOT SEE ANY O2 PRESSURE CHANGE ON AIRCRAFT ON THE DAY IN QUESTION.CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: REPORTER STATED THAT THE VALVE HANDLE OF THE O2 BOTTLE INVOLVED WAS ONLY OPEN 3 TURNS INSTEAD OF THE FULL 6 TURNS PRESCRIBED IN THE MAINTENANCE MANUAL. THIS VALVE POSITION STILL ALLOWED FULL O2 FLOW BUT DID NOT MEET THE PREFLT REQUIREMENTS. THE VALVE POSITION IS A MAINTENANCE FUNCTION BECAUSE THE BOTTLE AND VALVE ARE LOCATED IN THE E AND E COMPARTMENT; INACCESSIBLE TO THE FLT CREW. HOWEVER; THE REPORTER'S ACR EXPECTS THE FLT CREW TO OBSERVE THE O2 BOTTLE PRESSURE FOR A PRESSURE DROP DURING O2 MASK CHECKING. HOWEVER; UNLESS THE BOTTLE VALVE IS NEARLY CLOSED; THE REPORTER STATED THAT THERE IS NEVER A DROP IN PRESSURE DURING THE CHECK; THEREFORE THE FLT CREW HAS ABSOLUTELY NO WAY OF KNOWING IF THE VALVE IS FULLY OR PARTIALLY OPEN.

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.