Narrative:

Crew called me in maintenance control; said they were late and needed a deferral on crew fixed oxygen. It was at 900 psi in ZZZ1. They stated they had no problem flying below 10000 ft to ZZZ2 and back. I checked with dispatch and they concurred. Pilot stated he wasn't sure where the chart was at; and I also was blank on where to find it. I did find it in the back of the MEL book in the appendix; misread the chart; issued a deferral and flew the aircraft on a round trip ZZZ-ZZZ2-ZZZ1 below 10000 ft. In ZZZ on return trip; had ZZZ1 service the oxygen and clear the deferral. Callback conversation with reporter revealed the following information: the reporter stated the MEL was not used as the referencing authority/authorized for deferring the crew oxygen system. The reporter admits the error in using the special item list as the deferral authority/authorized. The special item list is for administrative use only; as it lists special items that are open or a maintenance item that makes this airplane different from the rest of the fleet. An uncompleted modification; passenger seat confign; are items that would be listed in the special item list.

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Original NASA ASRS Text

Title: A DHC8-200 WAS DISPATCHED WITH THE CREW OXYGEN OUT OF LIMITS. ITEM DEFERRED WITH LIMITED ALT RESTR. THE REFERENCE USED FOR DEFERRAL AUTH WAS INCORRECT.

Narrative: CREW CALLED ME IN MAINT CTL; SAID THEY WERE LATE AND NEEDED A DEFERRAL ON CREW FIXED OXYGEN. IT WAS AT 900 PSI IN ZZZ1. THEY STATED THEY HAD NO PROB FLYING BELOW 10000 FT TO ZZZ2 AND BACK. I CHKED WITH DISPATCH AND THEY CONCURRED. PLT STATED HE WASN'T SURE WHERE THE CHART WAS AT; AND I ALSO WAS BLANK ON WHERE TO FIND IT. I DID FIND IT IN THE BACK OF THE MEL BOOK IN THE APPENDIX; MISREAD THE CHART; ISSUED A DEFERRAL AND FLEW THE ACFT ON A ROUND TRIP ZZZ-ZZZ2-ZZZ1 BELOW 10000 FT. IN ZZZ ON RETURN TRIP; HAD ZZZ1 SVC THE OXYGEN AND CLR THE DEFERRAL. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THE RPTR STATED THE MEL WAS NOT USED AS THE REFERENCING AUTH FOR DEFERRING THE CREW OXYGEN SYS. THE RPTR ADMITS THE ERROR IN USING THE SPECIAL ITEM LIST AS THE DEFERRAL AUTH. THE SPECIAL ITEM LIST IS FOR ADMINISTRATIVE USE ONLY; AS IT LISTS SPECIAL ITEMS THAT ARE OPEN OR A MAINT ITEM THAT MAKES THIS AIRPLANE DIFFERENT FROM THE REST OF THE FLEET. AN UNCOMPLETED MODIFICATION; PAX SEAT CONFIGN; ARE ITEMS THAT WOULD BE LISTED IN THE SPECIAL ITEM LIST.

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