Narrative:

During a normal climb to assigned altitude of FL230 and coming out of FL200, both pilots confirmed the cabin was not pressurizing. In notifying center, we were experiencing pressurization problems and we needed to descend immediately and return to ZZZ, our base of operations. We were cleared 'direct ZZZ descend to maintain FL190.' I told the first officer to tell them we needed lower than FL190, which he did. We were then cleared to maintain 17000 ft. During this conversation with center, the first officer and myself were busy with donning oxygen masks, communicating, and executing an emergency descent to the assigned altitude and maneuvering the airplane 180 degrees to direct ZZZ. The highest altitude I recall seeing on the altimeter was FL204 when we started down. In a hawker 400 with power to idle and speed brakes fully deployed and airspeed to the barber pole, which was 300 KTS, it will not take very long to come down 3000 ft to our assigned altitude of 17000 ft. Keeping in mind, during our climb the cabin never pressurized. My copilot and myself were both experiencing hypoxia and that uneasy, lightheaded feeling from lack of oxygen. During the emergency descent procedure and now on oxygen but not fully recovered 100% I descended through 17000 ft and arrested the descent at 15000 ft. Center asked if we had continued on down to 15000 ft. We answered we had and that we needed to get down. At this time center handed us off to probably another center frequency (I really can't recall at this time) and eventually to ZZZ approach. Once in ZZZ approach control's airspace we advised them we needed to burn fuel off before attempting a landing. They vectored us to remain within 15 mi of the VOR and to descend to 4000 ft, which we did. Once we started descending out of 15000 ft, we were at a mental level to troubleshoot the situation. Completing the checklist, we were dumbfounded as to why we did not pressurize. Once we were with approach and brought them up to speed of the situation, we recycled the main air valves and regained control of the pressurization. The cabin pressurized and we requested 10000 ft which was approved and we tested the ability of the controller to maintain the cabin altitude selected which worked faultlessly. We were both comfortable with the problem being satisfied and continued on the assigned trip with no further occurrences.

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Original NASA ASRS Text

Title: H25 FLT CREW ATTRIBUTED ALT OVERSHOOT TO HYPOXIA RESULTING FROM PRESSURIZATION FAILURE.

Narrative: DURING A NORMAL CLB TO ASSIGNED ALT OF FL230 AND COMING OUT OF FL200, BOTH PLTS CONFIRMED THE CABIN WAS NOT PRESSURIZING. IN NOTIFYING CTR, WE WERE EXPERIENCING PRESSURIZATION PROBS AND WE NEEDED TO DSND IMMEDIATELY AND RETURN TO ZZZ, OUR BASE OF OPS. WE WERE CLRED 'DIRECT ZZZ DSND TO MAINTAIN FL190.' I TOLD THE FO TO TELL THEM WE NEEDED LOWER THAN FL190, WHICH HE DID. WE WERE THEN CLRED TO MAINTAIN 17000 FT. DURING THIS CONVERSATION WITH CTR, THE FO AND MYSELF WERE BUSY WITH DONNING OXYGEN MASKS, COMMUNICATING, AND EXECUTING AN EMER DSCNT TO THE ASSIGNED ALT AND MANEUVERING THE AIRPLANE 180 DEGS TO DIRECT ZZZ. THE HIGHEST ALT I RECALL SEEING ON THE ALTIMETER WAS FL204 WHEN WE STARTED DOWN. IN A HAWKER 400 WITH PWR TO IDLE AND SPD BRAKES FULLY DEPLOYED AND AIRSPD TO THE BARBER POLE, WHICH WAS 300 KTS, IT WILL NOT TAKE VERY LONG TO COME DOWN 3000 FT TO OUR ASSIGNED ALT OF 17000 FT. KEEPING IN MIND, DURING OUR CLB THE CABIN NEVER PRESSURIZED. MY COPLT AND MYSELF WERE BOTH EXPERIENCING HYPOXIA AND THAT UNEASY, LIGHTHEADED FEELING FROM LACK OF OXYGEN. DURING THE EMER DSCNT PROC AND NOW ON OXYGEN BUT NOT FULLY RECOVERED 100% I DSNDED THROUGH 17000 FT AND ARRESTED THE DSCNT AT 15000 FT. CTR ASKED IF WE HAD CONTINUED ON DOWN TO 15000 FT. WE ANSWERED WE HAD AND THAT WE NEEDED TO GET DOWN. AT THIS TIME CTR HANDED US OFF TO PROBABLY ANOTHER CTR FREQ (I REALLY CAN'T RECALL AT THIS TIME) AND EVENTUALLY TO ZZZ APCH. ONCE IN ZZZ APCH CTL'S AIRSPACE WE ADVISED THEM WE NEEDED TO BURN FUEL OFF BEFORE ATTEMPTING A LNDG. THEY VECTORED US TO REMAIN WITHIN 15 MI OF THE VOR AND TO DSND TO 4000 FT, WHICH WE DID. ONCE WE STARTED DSNDING OUT OF 15000 FT, WE WERE AT A MENTAL LEVEL TO TROUBLESHOOT THE SIT. COMPLETING THE CHKLIST, WE WERE DUMBFOUNDED AS TO WHY WE DID NOT PRESSURIZE. ONCE WE WERE WITH APCH AND BROUGHT THEM UP TO SPD OF THE SIT, WE RECYCLED THE MAIN AIR VALVES AND REGAINED CTL OF THE PRESSURIZATION. THE CABIN PRESSURIZED AND WE REQUESTED 10000 FT WHICH WAS APPROVED AND WE TESTED THE ABILITY OF THE CTLR TO MAINTAIN THE CABIN ALT SELECTED WHICH WORKED FAULTLESSLY. WE WERE BOTH COMFORTABLE WITH THE PROB BEING SATISFIED AND CONTINUED ON THE ASSIGNED TRIP WITH NO FURTHER OCCURRENCES.

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.