Narrative:

While performing an ETOPS check on a B757-200 aircraft june 2011; I noticed crew oxygen (O2) was low. On several occasions tried to determine what was the minimum O2 pressure for dispatch and was unable to figure out. Maintenance manual (MM) 35-10-99 has a graph that is vague and not easily understood. I notified company maintenance control that we suspected [crew] O2 was low and had no way to service. That we really could not tell what line on figure-201 was the low limit line that the MM instructs us to use a filling chart placard on the service door that was not present on any B757 we had that day. I was instructed to use the pilot flight manual's limit as my limit; that this manual was an approved source. I questioned how we could use a manual specification that we had no access to and would not know if it was current. Maintenance control informed me that the value would never change so don't worry. My concern is the pilot's manual allows the plane to be dispatched with pressure as low as 480 psi and I don't feel this is a safe level for ETOPS dispatch. This was the third plane in a week that left with crew 02 below 1350.

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Original NASA ASRS Text

Title: A Line Mechanic reports he was instructed by Maintenance Control to use the Pilot's Flight Manual as a reference source to sign-off a low Crew Oxygen (O2) bottle reading for an over water B757-200 ETOPS flight. Lack of proper equipment and difficulty determining the correct O2 level using the Maintenance Manual (MM) Chapter 35-10-99 graph were also noted.

Narrative: While performing an ETOPS Check on a B757-200 aircraft June 2011; I noticed Crew Oxygen (O2) was low. On several occasions tried to determine what was the minimum O2 pressure for dispatch and was unable to figure out. Maintenance Manual (MM) 35-10-99 has a graph that is vague and not easily understood. I notified company Maintenance Control that we suspected [Crew] O2 was low and had no way to service. That we really could not tell what line on Figure-201 was the Low limit line that the MM instructs us to use a Filling chart placard on the Service door that was not present on any B757 we had that day. I was instructed to use the Pilot Flight Manual's limit as my limit; that this manual was an approved source. I questioned how we could use a manual specification that we had no access to and would not know if it was current. Maintenance Control informed me that the value would never change so don't worry. My concern is the Pilot's manual allows the plane to be dispatched with pressure as low as 480 psi and I don't feel this is a safe level for ETOPS dispatch. This was the third plane in a week that left with crew 02 below 1350.

Data retrieved from NASA's ASRS site as of April 2012 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.