Narrative:

I was ferrying a C208 that was newly acquired by my company. I departed boi en route to mtn with a planned fuel stop en route. I conducted an acceptance flight on oct/xa/99 and found all system in proper working order. The oxygen gauge showed about 900 pounds. I climbed to FL190 using supplemental oxygen above 10000 ft. About 3 hours later with the oxygen gauge showing 350 pounds, I realized I was experiencing hypoxia. At the time I was near the sidney, northeast, airport. I told ZDV that I needed to land. I may have descended from FL190 before being cleared. I did cancel IFR in the air and also called FSS to report I was down safely. I would never fly an unknown aircraft into hard IFR at altitudes that require oxygen without knowing that oxygen system on the airplane was accurate.

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Original NASA ASRS Text

Title: PLT OF AN ATX CESSNA 208 ON FERRY FLT EXPERIENCED HYPOXIA DURING 3 HR FLT AT FL190 DUE TO MALFUNCTIONING OXYGEN SYS, AND DIVERTED TO LAND FOR FUEL EARLIER THAN PLANNED.

Narrative: I WAS FERRYING A C208 THAT WAS NEWLY ACQUIRED BY MY COMPANY. I DEPARTED BOI ENRTE TO MTN WITH A PLANNED FUEL STOP ENRTE. I CONDUCTED AN ACCEPTANCE FLT ON OCT/XA/99 AND FOUND ALL SYS IN PROPER WORKING ORDER. THE OXYGEN GAUGE SHOWED ABOUT 900 LBS. I CLBED TO FL190 USING SUPPLEMENTAL OXYGEN ABOVE 10000 FT. ABOUT 3 HRS LATER WITH THE OXYGEN GAUGE SHOWING 350 LBS, I REALIZED I WAS EXPERIENCING HYPOXIA. AT THE TIME I WAS NEAR THE SIDNEY, NE, ARPT. I TOLD ZDV THAT I NEEDED TO LAND. I MAY HAVE DSNDED FROM FL190 BEFORE BEING CLRED. I DID CANCEL IFR IN THE AIR AND ALSO CALLED FSS TO RPT I WAS DOWN SAFELY. I WOULD NEVER FLY AN UNKNOWN ACFT INTO HARD IFR AT ALTS THAT REQUIRE OXYGEN WITHOUT KNOWING THAT OXYGEN SYS ON THE AIRPLANE WAS ACCURATE.

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.