Narrative:

After descending from FL320 to FL310 (ATC had requested FL330 but I was unable to accept because speed was already low at .725 mach and throttles were at maximum EPR because of downdraft / turbulence while penetrating line of thunderstorms). While cruising at FL310; the cockpit observer noticed the flow light was illuminated on the pressurization control box. He brought it to my attention and I decided that since the OAT was -16C and we were now clear of the turbulence; that I would turn off the airfoil anti-ice to see if that would remedy the problem. Unfortunately; the flow light remained on; and the cabin continued to climb at 500 FPM. We then consulted the QRH and accomplished the checklist items therein to no avail. The cabin altitude was now about 7;500 ft. We then asked ATC for lower and descended quickly to FL290 now the cabin was climbing at 600 FPM plus and the cabin altitude was at 9;000 ft. At this point I asked for further descent; declared an emergency and asked for a vector to a nearby airport. We were given clearance for the diversion and clearance to descent to 10;000 ft. While passing FL210 the pressure appeared to stabilize and we eventually leveled off at 14;000 ft.

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Original NASA ASRS Text

Title: MD83 Captain is informed of a flow light at FL310 by a pilot on the jumpseat. The airfoil anti ice is turned off to no avail. Flight descends to 14;000 FT and diverts to a suitable airport.

Narrative: After descending from FL320 to FL310 (ATC had requested FL330 but I was unable to accept because speed was already low at .725 mach and throttles were at maximum EPR because of downdraft / turbulence while penetrating line of thunderstorms). While cruising at FL310; the cockpit observer noticed the flow light was illuminated on the pressurization control box. He brought it to my attention and I decided that since the OAT was -16C and we were now clear of the turbulence; that I would turn off the airfoil anti-ice to see if that would remedy the problem. Unfortunately; the flow light remained on; and the cabin continued to climb at 500 FPM. We then consulted the QRH and accomplished the checklist items therein to no avail. The cabin altitude was now about 7;500 FT. We then asked ATC for lower and descended quickly to FL290 now the cabin was climbing at 600 FPM plus and the cabin altitude was at 9;000 FT. At this point I asked for further descent; declared an emergency and asked for a vector to a nearby airport. We were given clearance for the diversion and clearance to descent to 10;000 FT. While passing FL210 the pressure appeared to stabilize and we eventually leveled off at 14;000 FT.

Data retrieved from NASA's ASRS site as of April 2012 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.