Narrative:

I was assigned 2 gates. Aircraft arrived with an oxygen indication problem. Log page states oxygen pressure indicator inoperative; oxygen checked normal prior to departure. Enroute pressure indication fluctuates between 1;100 - 0 psi. I met the crew and discussed the problem. Checked oxygen pressure at the cylinder gauge and oxygen flow at the mask and supply normal. I read the fim and decided to replace the oxygen pressure transducer. I ordered the part through my lead and went to my other assigned gate. When the part arrived; there was not enough time to replace the part and avoid a lengthy delay since the oxygen cylinder is located in forward cargo compartment and rampers were loading baggage. I decided to defer the item per MEL. I opened log page and verified oxygen pressure to be 1;100 psi on the cylinder gauge. I concluded that the problem was indication after checking the flow of oxygen in the mask. Also verified with crew that the mask test was normal. I overlooked the dispatch deviation procedures portion; which states; verify the crew oxygen cylinder shutoff valve is open; since the last time the oxygen bottle was serviced was 2 months earlier per log page. According to the history of crew oxygen on this aircraft; there was no problem until now and I concluded the flow was normal; and I did not cut the safety wire and check the valve opening. I probably should not have followed this logic or checked the history. This is the mistake I made; and I will try to correct this. Verify MEL requirements via checklist style.

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Original NASA ASRS Text

Title: After deferring a B737 crew oxygen pressure indication for fluctuations; Mechanic failed to notice the Dispatch Deviation Procedures (DDP) requirement to verify the crew oxygen bottle valve handle was full open at the bottle.

Narrative: I was assigned 2 gates. Aircraft arrived with an oxygen indication problem. Log page states oxygen pressure indicator inoperative; oxygen checked normal prior to departure. Enroute pressure indication fluctuates between 1;100 - 0 PSI. I met the crew and discussed the problem. Checked oxygen pressure at the cylinder gauge and oxygen flow at the mask and supply normal. I read the FIM and decided to replace the oxygen pressure transducer. I ordered the part through my Lead and went to my other assigned gate. When the part arrived; there was not enough time to replace the part and avoid a lengthy delay since the oxygen cylinder is located in forward cargo compartment and Rampers were loading baggage. I decided to defer the item per MEL. I opened log page and verified oxygen pressure to be 1;100 PSI on the cylinder gauge. I concluded that the problem was indication after checking the flow of oxygen in the mask. Also verified with crew that the mask test was normal. I overlooked the Dispatch Deviation Procedures portion; which states; verify the crew oxygen cylinder shutoff valve is open; since the last time the oxygen bottle was serviced was 2 months earlier per log page. According to the history of crew oxygen on this aircraft; there was no problem until now and I concluded the flow was normal; and I did not cut the safety wire and check the valve opening. I probably should not have followed this logic or checked the history. This is the mistake I made; and I will try to correct this. Verify MEL requirements via checklist style.

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.