Narrative:

I was called by the B757 flight crew and informed of a logbook write-up of a low crew oxygen cylinder pressure. I noted the cylinder pressure on the EICAS panel and returned to the maintenance office to contact maintenance coordinator's office in ZZZ1 and reported the write-up. Maintenance coordinator affirmed that the cylinder was below limits and needed to be replaced. I was informed by the coordinator that we had an air carrier X airline's oxygen cylinder in stock which was ok to use. Upon changing the cylinder I noticed the overboard vent line union on the new cylinder was different, so I swapped the union from the old cylinder to the new one, which I now know is an illegal modification. I then did my leak check and operations check of the system. Everything checked out ok, and I signed off the logbook.

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Original NASA ASRS Text

Title: A B757-200 WAS DISPATCHED IN NON COMPLIANCE WITH A BORROWED CREW OXYGEN CYLINDER BUT MODIFIED BY A LCL TECHNICIAN TO FIT.

Narrative: I WAS CALLED BY THE B757 FLC AND INFORMED OF A LOGBOOK WRITE-UP OF A LOW CREW OXYGEN CYLINDER PRESSURE. I NOTED THE CYLINDER PRESSURE ON THE EICAS PANEL AND RETURNED TO THE MAINT OFFICE TO CONTACT MAINT COORDINATOR'S OFFICE IN ZZZ1 AND RPTED THE WRITE-UP. MAINT COORDINATOR AFFIRMED THAT THE CYLINDER WAS BELOW LIMITS AND NEEDED TO BE REPLACED. I WAS INFORMED BY THE COORDINATOR THAT WE HAD AN ACR X AIRLINE'S OXYGEN CYLINDER IN STOCK WHICH WAS OK TO USE. UPON CHANGING THE CYLINDER I NOTICED THE OVERBOARD VENT LINE UNION ON THE NEW CYLINDER WAS DIFFERENT, SO I SWAPPED THE UNION FROM THE OLD CYLINDER TO THE NEW ONE, WHICH I NOW KNOW IS AN ILLEGAL MODIFICATION. I THEN DID MY LEAK CHK AND OPS CHK OF THE SYS. EVERYTHING CHKED OUT OK, AND I SIGNED OFF THE LOGBOOK.

Data retrieved from NASA's ASRS site as of July 2007 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.