Narrative:

After departing den en route to gunnison, co, in the en route environment, cabin altitude high annunciator briefly illuminated. My first officer had set the pressurization controller a bit too high, so he then adjusted it to a lower cruise altitude. The annunciator went off a few moments later. The cabin altitude, according to the pressurization gauge, never went above 10000 ft. It indicated about 9500 ft only. Had our adjustment of the pressurization controller not halted the cabin altitude's climb, we would have deployed the crew and passenger oxygen masks. The sensor associated with the annunciator in this series of aircraft is famous for illuminating too soon. The aircraft manufacturer's checklist calls for the crew and passenger oxygen masks to be deployed and worn immediately upon illumination of the cabin altitude high annunciator. Next time we will deploy the oxygen masks as required, because we have no way as crew of knowing whether the sensor is inaccurate or the pressurization window is inaccurate.

Related reports:

Google
 

Original NASA ASRS Text

Title: A BEECH 1900D IN CLB EXPERIENCED THE 'CAB ALT HIGH' WARNING LIGHT COME ON AND GO OUT A FEW MOMENTS LATER. THE CREW DID NOT DEPLOY THE EMER OXYGEN MASKS PER THE OPERATING MANUAL.

Narrative: AFTER DEPARTING DEN ENRTE TO GUNNISON, CO, IN THE ENRTE ENVIRONMENT, CABIN ALT HIGH ANNUNCIATOR BRIEFLY ILLUMINATED. MY FO HAD SET THE PRESSURIZATION CTLR A BIT TOO HIGH, SO HE THEN ADJUSTED IT TO A LOWER CRUISE ALT. THE ANNUNCIATOR WENT OFF A FEW MOMENTS LATER. THE CABIN ALT, ACCORDING TO THE PRESSURIZATION GAUGE, NEVER WENT ABOVE 10000 FT. IT INDICATED ABOUT 9500 FT ONLY. HAD OUR ADJUSTMENT OF THE PRESSURIZATION CTLR NOT HALTED THE CABIN ALT'S CLB, WE WOULD HAVE DEPLOYED THE CREW AND PAX OXYGEN MASKS. THE SENSOR ASSOCIATED WITH THE ANNUNCIATOR IN THIS SERIES OF ACFT IS FAMOUS FOR ILLUMINATING TOO SOON. THE ACFT MANUFACTURER'S CHKLIST CALLS FOR THE CREW AND PAX OXYGEN MASKS TO BE DEPLOYED AND WORN IMMEDIATELY UPON ILLUMINATION OF THE CABIN ALT HIGH ANNUNCIATOR. NEXT TIME WE WILL DEPLOY THE OXYGEN MASKS AS REQUIRED, BECAUSE WE HAVE NO WAY AS CREW OF KNOWING WHETHER THE SENSOR IS INACCURATE OR THE PRESSURIZATION WINDOW IS INACCURATE.

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.