Narrative:

Cruise: deviating to the north of thunderstorms. Engine and wing anti-ice on. Noticed flow light on overhead panel and cabin altitude climbing 500 FPM. Followed QRH flow light procedure. Cabin momentarily began descending then resumed 500 FPM climb. Received clearance to FL310; cabin fluctuating between 500 FPM climb and 100-200 FPM descent during descent. After brief leveloff at FL310; received clearance to FL250; while descending kept power up at 1.6 EPR and speed brake deployed. Nearing leveloff at FL240 cabin began 1000+ FPM climb. Followed QRH rapid depressurization procedure; then emergency descent procedure; receiving clearance to 10000 ft; declared emergency. Cabin altitude increased above 10000 ft and received cabin altitude warning. After leveloff at 10000; determined nearest suitable airport to be ZZZ. Received clearance to proceed direct to the airport; landing without clearance. Although an emergency was declared; I do not think we deviated from any clearance; however; it was quite busy and it is possible that we did; inadvertently. Callback conversation with reporter revealed the following information: the first officer did not know what repairs were required to return the aircraft to service. The wing anti-ice system goes into an automatic cycle lasting 1.5 minutes when it is turned off so the flight crew was unable to direct bleed air to the packs only in a timely manner.

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Original NASA ASRS Text

Title: MD80 FLT CREW EXPERIENCES LOW FLOW AT FL330 WITH WING AND ENGINE ANTI-ICE ON. CABIN ALTITUDE BEGINS TO CLIMB AND AN EMERGENCY DESCENT IS INITIATED WITH LANDING AT NEAREST SUITABLE ARPT.

Narrative: CRUISE: DEVIATING TO THE N OF TSTMS. ENG AND WING ANTI-ICE ON. NOTICED FLOW LIGHT ON OVERHEAD PANEL AND CABIN ALT CLBING 500 FPM. FOLLOWED QRH FLOW LIGHT PROC. CABIN MOMENTARILY BEGAN DSNDING THEN RESUMED 500 FPM CLB. RECEIVED CLRNC TO FL310; CABIN FLUCTUATING BTWN 500 FPM CLB AND 100-200 FPM DSCNT DURING DSCNT. AFTER BRIEF LEVELOFF AT FL310; RECEIVED CLRNC TO FL250; WHILE DSNDING KEPT PWR UP AT 1.6 EPR AND SPD BRAKE DEPLOYED. NEARING LEVELOFF AT FL240 CABIN BEGAN 1000+ FPM CLB. FOLLOWED QRH RAPID DEPRESSURIZATION PROC; THEN EMER DSCNT PROC; RECEIVING CLRNC TO 10000 FT; DECLARED EMER. CABIN ALT INCREASED ABOVE 10000 FT AND RECEIVED CABIN ALT WARNING. AFTER LEVELOFF AT 10000; DETERMINED NEAREST SUITABLE ARPT TO BE ZZZ. RECEIVED CLRNC TO PROCEED DIRECT TO THE ARPT; LWOC. ALTHOUGH AN EMER WAS DECLARED; I DO NOT THINK WE DEVIATED FROM ANY CLRNC; HOWEVER; IT WAS QUITE BUSY AND IT IS POSSIBLE THAT WE DID; INADVERTENTLY. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THE FIRST OFFICER DID NOT KNOW WHAT REPAIRS WERE REQUIRED TO RETURN THE ACFT TO SERVICE. THE WING ANTI-ICE SYSTEM GOES INTO AN AUTOMATIC CYCLE LASTING 1.5 MINUTES WHEN IT IS TURNED OFF SO THE FLT CREW WAS UNABLE TO DIRECT BLEED AIR TO THE PACKS ONLY IN A TIMELY MANNER.

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.