While performing a crew oxygen mask check on a B737-800 aircraft; a captain observed the crew oxygen...

Attributes
ACN	1076902
Time
Date	201303
Local Time Of Day	1201-1800
Place
Locale Reference	ZZZ.Airport
State Reference	US
Environment
Light	Daylight
Aircraft 1
Make Model Name	B737-800
Operating Under FAR Part	Part 121
Flight Phase	Parked
Component
Aircraft Component	Oxygen System/Crew
Person 1
Function	Pilot Flying Captain
Qualification	Flight Crew Air Transport Pilot (ATP)
Events
Anomaly	Aircraft Equipment Problem Critical Deviation - Procedural Published Material / Policy

Narrative:

As I was testing my oxygen mask; while looking at the crew oxygen pressure; I observed the pressure drop from 1;870 psi to 1;800 psi in about 10-seconds and not recover. A second test resulted in a similar result: the crew oxygen pressure dropped and did not recover. Maintenance was notified and discovered the crew oxygen bottle valve was not fully open. The valve was fully opened and safety wired by maintenance. Crew oxygen pressure did not drop during subsequent tests of my oxygen mask. As the crew oxygen bottle pressure was about 1;900 psi at the start of my first mask test; I suspect the oxygen bottle was recently installed. Ensure all maintainers are familiar with the proper procedure for B737 crew oxygen bottle installation.

Original NASA ASRS Text

Title: While performing a Crew Oxygen Mask Check on a B737-800 aircraft; a Captain observed the Crew Oxygen Pressure drop from 1;870 PSI down to 1;800 PSI in about 10-seconds and not recover. Maintenance found the Crew Oxygen Bottle Valve not fully opened.

Narrative: As I was testing my oxygen mask; while looking at the Crew Oxygen Pressure; I observed the pressure drop from 1;870 PSI to 1;800 PSI in about 10-seconds and not recover. A second test resulted in a similar result: the Crew Oxygen Pressure dropped and did not recover. Maintenance was notified and discovered the Crew Oxygen Bottle Valve was not fully open. The valve was fully opened and safety wired by Maintenance. Crew Oxygen Pressure did not drop during subsequent tests of my oxygen mask. As the Crew Oxygen Bottle Pressure was about 1;900 PSI at the start of my first mask test; I suspect the oxygen bottle was recently installed. Ensure all maintainers are familiar with the proper procedure for B737 Crew Oxygen Bottle installation.

Data retrieved from NASA's ASRS site as of July 2013 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.

While performing a crew oxygen mask check on a B737-800 aircraft; a captain observed the crew oxygen pressure drop from 1;870 psi down to 1;800 psi in about 10-seconds and not recover. Maintenance found the crew oxygen bottle valve not fully opened.