B737 pressurization controller failed; increasing pressure in cabin.

Attributes
ACN	737702
Time
Date	200705
Local Time Of Day	0601 To 1200
Place
Locale Reference	navaid : ood.vortac
State Reference	NJ
Altitude	msl bound lower : 28000 msl bound upper : 29000
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	artcc : zdc.artcc
Operator	common carrier : air carrier
Make Model Name	B737-700
Operating Under FAR Part	Part 121
Navigation In Use	other
Flight Phase	climbout : intermediate altitude
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Experience	flight time last 90 days : 215
ASRS Report	737702
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Experience	flight time last 90 days : 195 flight time type : 3000
ASRS Report	737497
Events
Anomaly	aircraft equipment problem : critical
Independent Detector	other flight crewa other flight crewb
Resolutory Action	other
Supplementary
Problem Areas	Aircraft
Primary Problem	Aircraft

Narrative:

Passing FL280 for FL290; cabin began intense descent; driving the cabin altitude down from approximately 4000 to 0; and differential pressure toward the yellow arc. Associated ear and sinus discomfort to crew and passenger was strong. The cabin then reversed course towards a climb; then back to an intense 4000 FPM plus descent. I briefed to begin the memory items for abnormal pressurization checklist. I attempted to alleviate some of the pressure by turning off the left pack; with little or no change. Subsequently; the first officer also thought to turn off the right pack; and we were momentarily depressurized; but I turned the pack back on immediately. The cabin continued wild gyrations from an appropriate cabin altitude to rapid descent; maximum differential; and back to rapid climb. The cabin altitude horn then went off with a cabin altitude approaching 11000 ft. At no time were there any associated system faults or master cautions. After establishing crew communications; I continued the abnormal pressurization checklist and operated the pressurization in manual mode; which did stop the cabin from climbing further or a fast descent. We asked ATC for lower and an immediate return to bwi. Subsequent approach and landing were uneventful. Add procedures/training for differential exceedance.

Original NASA ASRS Text

Title: B737 PRESSURIZATION CONTROLLER FAILED; INCREASING PRESSURE IN CABIN.

Narrative: PASSING FL280 FOR FL290; CABIN BEGAN INTENSE DSCNT; DRIVING THE CABIN ALT DOWN FROM APPROX 4000 TO 0; AND DIFFERENTIAL PRESSURE TOWARD THE YELLOW ARC. ASSOCIATED EAR AND SINUS DISCOMFORT TO CREW AND PAX WAS STRONG. THE CABIN THEN REVERSED COURSE TOWARDS A CLB; THEN BACK TO AN INTENSE 4000 FPM PLUS DSCNT. I BRIEFED TO BEGIN THE MEMORY ITEMS FOR ABNORMAL PRESSURIZATION CHKLIST. I ATTEMPTED TO ALLEVIATE SOME OF THE PRESSURE BY TURNING OFF THE L PACK; WITH LITTLE OR NO CHANGE. SUBSEQUENTLY; THE FO ALSO THOUGHT TO TURN OFF THE R PACK; AND WE WERE MOMENTARILY DEPRESSURIZED; BUT I TURNED THE PACK BACK ON IMMEDIATELY. THE CABIN CONTINUED WILD GYRATIONS FROM AN APPROPRIATE CABIN ALT TO RAPID DSCNT; MAX DIFFERENTIAL; AND BACK TO RAPID CLB. THE CABIN ALT HORN THEN WENT OFF WITH A CABIN ALT APCHING 11000 FT. AT NO TIME WERE THERE ANY ASSOCIATED SYS FAULTS OR MASTER CAUTIONS. AFTER ESTABLISHING CREW COMS; I CONTINUED THE ABNORMAL PRESSURIZATION CHKLIST AND OPERATED THE PRESSURIZATION IN MANUAL MODE; WHICH DID STOP THE CABIN FROM CLBING FURTHER OR A FAST DSCNT. WE ASKED ATC FOR LOWER AND AN IMMEDIATE RETURN TO BWI. SUBSEQUENT APCH AND LNDG WERE UNEVENTFUL. ADD PROCS/TRAINING FOR DIFFERENTIAL EXCEEDANCE.

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.