A B737NG flight crew found during preflight their crew oxygen bottle supply valve was only half open...

Attributes
ACN	808805
Time
Date	200810
Local Time Of Day	0601 To 1200
Place
Locale Reference	airport : zzz.airport
State Reference	US
Altitude	agl single value : 0
Environment
Flight Conditions	VMC
Light	Dawn
Aircraft 1
Operator	common carrier : air carrier
Make Model Name	B737 Undifferentiated or Other Model
Operating Under FAR Part	Part 121
Flight Phase	ground : preflight
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Experience	flight time last 90 days : 154 flight time type : 154
ASRS Report	808805
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Experience	flight time last 90 days : 197
ASRS Report	808802
Events
Anomaly	aircraft equipment problem : critical maintenance problem : improper maintenance
Independent Detector	other flight crewa
Resolutory Action	none taken : detected after the fact
Consequence	other
Supplementary
Problem Areas	Flight Crew Human Performance Maintenance Human Performance Aircraft
Primary Problem	Maintenance Human Performance

Narrative:

The flight was flown with the crew oxygen system supply valve only half open. During preflight; cockpit indications were normal and the gauge showed approximately 1500 psi. My oxygen test was performed properly and there was no movement on the psi indication as oxygen was released through the mask. The first officer performed his oxygen test immediately following mine. He watched the results of my test and the results of his own test; and the psi indication did not move at all showing a good test. The flight was uneventful. In preparation for the next flight; the first officer did his oxygen test first. This time he noticed the pressure was higher than before and the oxygen test caused the gauge indication to decrease about 300 psi during the test. He pointed out the discrepancy and I performed my test. The oxygen indicator was now showing about 1850 psi; and during the test the pressure would drop about 300 psi stabilizing between 1550 and 1600 psi. We made multiple test attempts with the same result. Maintenance was called and they found the oxygen supply valve only half open.supplemental information from acn 808802: the proper preflight action was taken on the O2 system by both pilots. I don't know why we didn't get the flux in psi during the originator preflight. The only thing I can think of to do is to check the mask pressure for a longer period of time. We were not notified of any O2 servicing if any occurred.

Original NASA ASRS Text

Title: A B737NG FLT CREW FOUND DURING PREFLIGHT THEIR CREW OXYGEN BOTTLE SUPPLY VALVE WAS ONLY HALF OPEN. THEY HAD ALREADY FLOWN ONE LEG BECAUSE THE BOTTLE APPEARED TO CHECK NORMAL.

Narrative: THE FLIGHT WAS FLOWN WITH THE CREW OXYGEN SYSTEM SUPPLY VALVE ONLY HALF OPEN. DURING PREFLIGHT; COCKPIT INDICATIONS WERE NORMAL AND THE GAUGE SHOWED APPROXIMATELY 1500 PSI. MY OXYGEN TEST WAS PERFORMED PROPERLY AND THERE WAS NO MOVEMENT ON THE PSI INDICATION AS OXYGEN WAS RELEASED THROUGH THE MASK. THE FO PERFORMED HIS OXYGEN TEST IMMEDIATELY FOLLOWING MINE. HE WATCHED THE RESULTS OF MY TEST AND THE RESULTS OF HIS OWN TEST; AND THE PSI INDICATION DID NOT MOVE AT ALL SHOWING A GOOD TEST. THE FLIGHT WAS UNEVENTFUL. IN PREPARATION FOR THE NEXT FLIGHT; THE FO DID HIS OXYGEN TEST FIRST. THIS TIME HE NOTICED THE PRESSURE WAS HIGHER THAN BEFORE AND THE OXYGEN TEST CAUSED THE GAUGE INDICATION TO DECREASE ABOUT 300 PSI DURING THE TEST. HE POINTED OUT THE DISCREPANCY AND I PERFORMED MY TEST. THE OXYGEN INDICATOR WAS NOW SHOWING ABOUT 1850 PSI; AND DURING THE TEST THE PRESSURE WOULD DROP ABOUT 300 PSI STABILIZING BETWEEN 1550 AND 1600 PSI. WE MADE MULTIPLE TEST ATTEMPTS WITH THE SAME RESULT. MAINTENANCE WAS CALLED AND THEY FOUND THE OXYGEN SUPPLY VALVE ONLY HALF OPEN.SUPPLEMENTAL INFO FROM ACN 808802: THE PROPER PREFLIGHT ACTION WAS TAKEN ON THE O2 SYSTEM BY BOTH PILOTS. I DON'T KNOW WHY WE DIDN'T GET THE FLUX IN PSI DURING THE ORIGINATOR PREFLIGHT. THE ONLY THING I CAN THINK OF TO DO IS TO CHECK THE MASK PRESSURE FOR A LONGER PERIOD OF TIME. WE WERE NOT NOTIFIED OF ANY O2 SERVICING IF ANY OCCURRED.

Data retrieved from NASA's ASRS site as of May 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.

A B737NG flight crew found during preflight their crew oxygen bottle supply valve was only half open. They had already flown one leg because the bottle appeared to check normal.