Narrative:

ZMA told me to 'cross rajay at 11000 ft.' I started my descent from 13000 ft. I was working on a pressurization problem with an airplane our company had just purchased. To give the mechanics a better idea of a pressurization problem which was MEL'ed, I noticed the airplane would pressurize in the manual mode. From miami airport I requested 17000 ft and noticed the cabin would not hold above at 9000 ft. So I requested 13000 ft and the cabin held at about 2000 ft. My vsi was a combination TCASII which had the back-lighting knob sheared, so I thought the vsi was inoperative. The bleed air in the airplane was tremendous. A high rate of air would come in through the eyelets, so much that it was a distraction. Even through my headsets I was deafened by the 'ssh' of the intense bleed air flow. With a new aircraft I had never flown before, and the above distractions, I was also manually tuning the cabin pressurization and I descended through my assigned altitude of 11000 ft, to 10500 ft. I quickly climbed to 11000 ft. I believe my preoccupation with the pressurization, no vsi and distraction of the intense bleed air were factors. The bleed air system was so loud I didn't hear the altitude 'ding.'

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Original NASA ASRS Text

Title: A SA227 INCURRED AN EXCURSION FROM AN ASSIGNED ALT DUE TO TROUBLESHOOTING THE PRESSURIZATION SYS.

Narrative: ZMA TOLD ME TO 'CROSS RAJAY AT 11000 FT.' I STARTED MY DSCNT FROM 13000 FT. I WAS WORKING ON A PRESSURIZATION PROB WITH AN AIRPLANE OUR COMPANY HAD JUST PURCHASED. TO GIVE THE MECHS A BETTER IDEA OF A PRESSURIZATION PROB WHICH WAS MEL'ED, I NOTICED THE AIRPLANE WOULD PRESSURIZE IN THE MANUAL MODE. FROM MIAMI ARPT I REQUESTED 17000 FT AND NOTICED THE CABIN WOULD NOT HOLD ABOVE AT 9000 FT. SO I REQUESTED 13000 FT AND THE CABIN HELD AT ABOUT 2000 FT. MY VSI WAS A COMBINATION TCASII WHICH HAD THE BACK-LIGHTING KNOB SHEARED, SO I THOUGHT THE VSI WAS INOP. THE BLEED AIR IN THE AIRPLANE WAS TREMENDOUS. A HIGH RATE OF AIR WOULD COME IN THROUGH THE EYELETS, SO MUCH THAT IT WAS A DISTRACTION. EVEN THROUGH MY HEADSETS I WAS DEAFENED BY THE 'SSH' OF THE INTENSE BLEED AIR FLOW. WITH A NEW ACFT I HAD NEVER FLOWN BEFORE, AND THE ABOVE DISTRACTIONS, I WAS ALSO MANUALLY TUNING THE CABIN PRESSURIZATION AND I DSNDED THROUGH MY ASSIGNED ALT OF 11000 FT, TO 10500 FT. I QUICKLY CLBED TO 11000 FT. I BELIEVE MY PREOCCUPATION WITH THE PRESSURIZATION, NO VSI AND DISTRACTION OF THE INTENSE BLEED AIR WERE FACTORS. THE BLEED AIR SYS WAS SO LOUD I DIDN'T HEAR THE ALT 'DING.'

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.