Narrative:

While climbing through FL200 we experienced a 'cabin altitude' information light and audible alarm. We did not get master warning or automatic deployment of oxygen masks. I looked at pressurization gauge and noticed that we did not have adequate differential and that the cabin altitude was approximately 10000 ft. I immediately grabbed my quick don mask; declared an emergency and initiated an emergency descent to 10000 ft. Once established in the descent; I began to try and troubleshoot the system by checking bleed air valves; environment controls; etc. Everything checked normal. The bleed system was on low (where it is normally kept). I turned the selector switch to normal and at about the same time noticed we were pressurizing again. We leveled at 10000 ft; went through all checks and determined we were pressurizing as normal. We informed ATC of what had taken place. They asked if we wanted to divert. We informed them that since the system were acting normal we would hang out at 10000 ft for a little bit and proceed to our destination. After a few more mins; we decided to step-climb the aircraft to FL210 and see how the system performed. There were no passenger on board. We asked for a step-climb and were told to climb our discretion to FL210. We then set in about an 800 FPM climb to FL210. The system acted completely normal. We continued to our destination without any further incident. We have contacted raytheon; and they are investigating. They believe that it could have been an indication issue; but have not finalized anything as of this report. I took and completed a hypoxia training course in december. I do not believe that I was at any time suffering from the effects of hypoxia. The aircraft checklists and fom require a pressurization check on initial climb. As a flight department; we are in the process of adding required checks at 10000 ft; FL180; and initial cruise; as well as ensuring that the pressure gauge is part of our normal scan.

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Original NASA ASRS Text

Title: B350 ENCOUNTERS TEMPORARY CABIN PRESSURIZATION FAILURE.

Narrative: WHILE CLBING THROUGH FL200 WE EXPERIENCED A 'CABIN ALT' INFO LIGHT AND AUDIBLE ALARM. WE DID NOT GET MASTER WARNING OR AUTO DEPLOYMENT OF OXYGEN MASKS. I LOOKED AT PRESSURIZATION GAUGE AND NOTICED THAT WE DID NOT HAVE ADEQUATE DIFFERENTIAL AND THAT THE CABIN ALT WAS APPROX 10000 FT. I IMMEDIATELY GRABBED MY QUICK DON MASK; DECLARED AN EMER AND INITIATED AN EMER DSCNT TO 10000 FT. ONCE ESTABLISHED IN THE DSCNT; I BEGAN TO TRY AND TROUBLESHOOT THE SYS BY CHKING BLEED AIR VALVES; ENVIRONMENT CTLS; ETC. EVERYTHING CHKED NORMAL. THE BLEED SYS WAS ON LOW (WHERE IT IS NORMALLY KEPT). I TURNED THE SELECTOR SWITCH TO NORMAL AND AT ABOUT THE SAME TIME NOTICED WE WERE PRESSURIZING AGAIN. WE LEVELED AT 10000 FT; WENT THROUGH ALL CHKS AND DETERMINED WE WERE PRESSURIZING AS NORMAL. WE INFORMED ATC OF WHAT HAD TAKEN PLACE. THEY ASKED IF WE WANTED TO DIVERT. WE INFORMED THEM THAT SINCE THE SYS WERE ACTING NORMAL WE WOULD HANG OUT AT 10000 FT FOR A LITTLE BIT AND PROCEED TO OUR DEST. AFTER A FEW MORE MINS; WE DECIDED TO STEP-CLB THE ACFT TO FL210 AND SEE HOW THE SYS PERFORMED. THERE WERE NO PAX ON BOARD. WE ASKED FOR A STEP-CLB AND WERE TOLD TO CLB OUR DISCRETION TO FL210. WE THEN SET IN ABOUT AN 800 FPM CLB TO FL210. THE SYS ACTED COMPLETELY NORMAL. WE CONTINUED TO OUR DEST WITHOUT ANY FURTHER INCIDENT. WE HAVE CONTACTED RAYTHEON; AND THEY ARE INVESTIGATING. THEY BELIEVE THAT IT COULD HAVE BEEN AN INDICATION ISSUE; BUT HAVE NOT FINALIZED ANYTHING AS OF THIS RPT. I TOOK AND COMPLETED A HYPOXIA TRAINING COURSE IN DECEMBER. I DO NOT BELIEVE THAT I WAS AT ANY TIME SUFFERING FROM THE EFFECTS OF HYPOXIA. THE ACFT CHKLISTS AND FOM REQUIRE A PRESSURIZATION CHK ON INITIAL CLB. AS A FLT DEPT; WE ARE IN THE PROCESS OF ADDING REQUIRED CHKS AT 10000 FT; FL180; AND INITIAL CRUISE; AS WELL AS ENSURING THAT THE PRESSURE GAUGE IS PART OF OUR NORMAL SCAN.

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.