PLT OF SMA UNPRESSURIZED ACFT EXPERIENCED HYPOXIA AT HIGH ALT DUE TO A MALFUNCTIONING OXYGEN SYS RESULTING IN EXCURSION FROM ASSIGNED ALT AND COURSE.

Narrative

FLYING A NON PRESSURIZED; TURBOCHARGED ACFT IN CLB TO FL210 WITH FACTORY INSTALLED OXYGEN SYS (FILLED FOR FLT BY EQUIP MANUFACTURER) AND MASK. DEVELOPED INTENSE HYPOXIA. PREFLT SHOWING OXYGEN FLOW. SYMPTOMS OF BUZZING IN HEAD; TINGLING OF FINGERS AND FEET AS WELL AS CONFUSION. IMMEDIATELY ASKED FOR LOWER ALT; BUT HAD DIFFICULTY MAINTAINING COURSE AND ALT PRIOR TO REQUEST. ALSO HAD DIFFICULTY PLOTTING RNAV RTE AND ENTERING DATA INTO EQUIP (SINGLE PLT). OF NOTE; I WAS MONITORING BLOOD OXYGEN SATURATION AS THIS WAS ONLY MY 2ND FLT HIGHER THAN 18000 FT; AND IT QUICKLY DROPPED TO 70 PERCENT. FURTHER FOR UNCLR REASONS (? HYPOXIA) MP DROPPED TO 15 INCHES JUST AFTER STARTING DSCNT BECAUSE OF HYPOXIA AND MALFUNCTIONING OXYGEN. ALTERNATE AIR HAD NO EFFECT AND I SUSPECTED TURBOCHARGER MALFUNCTION. AN EMER WAS DECLARED AND RADAR VECTORS TO THE CLOSEST ARPT WERE OBTAINED; LNDG WITHOUT INCIDENT. I AM CERTAINLY GLAD I CHOSE A VFR DAY AND MONITORED MY BLOOD OXYGEN SATURATION WHILE GETTING EARLY EXPERIENCE IN HIGHER ALT OPS. JUST BECAUSE ONE NOTES FLOWING OXYGEN ON PREFLT DOES NOT INSURE THAT HYPOXIA WILL NOT OCCUR. WE ARE STILL INVESTIGATING THE PROB.