Air carrier on descent has pressurization problem. Increase rate of descent, O2 masks drop.

Attributes
ACN	193640
Time
Date	199111
Day	Tue
Local Time Of Day	0601 To 1200
Place
Locale Reference	atc facility : hmv
State Reference	TN
Altitude	msl bound lower : 20000 msl bound upper : 20100
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	artcc : ztl
Operator	common carrier : air carrier
Make Model Name	Medium Large Transport, Low Wing, 2 Turbojet Eng
Flight Phase	descent other
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : cfi pilot : atp pilot : commercial pilot : flight engineer pilot : instrument
Experience	flight time last 90 days : 150 flight time total : 10000 flight time type : 185
ASRS Report	193640
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : instrument pilot : atp pilot : commercial
Events
Anomaly	aircraft equipment problem : critical
Independent Detector	other flight crewa
Resolutory Action	flight crew : declared emergency other
Consequence	Other
Supplementary
Primary Problem	Aircraft

Narrative:

On descending into tri while passing through 20100 MSL felt and saw cabin climbing full scale up (cabin altitude approximately 5000 ft). Told copilot who was flying to increase rate of descent to 6000 FPM to previously cleared altitude of 7000 ft MSL. Checked both packs on and outflow valve showed fully closed. As airplane passed through 14000+ cabin reached 14000 ft and O2 masks dropped in passenger cabin. 1 min later we were below 10000 ft and made PA for passenger to take off O2 masks. Later flight attendant said they heard loud hissing noise and felt cabin floor move under their ft in aft cabin. Also said they had to tell each passenger individually to put mask on because no passenger put them on when they dropped. Post-flight looked for ruptured ducts but could not find any. Called maintenance coordinator later. They said they had replaced the outflow valve. Since cabin climbed approximately 5000+ FPM would have been a handful at higher altitude without descent clearance on busy jetway or on full airplane with passenger not putting masks on since there was only 21 passenger. In this case more or less routine.

Original NASA ASRS Text

Title: ACR ON DSCNT HAS PRESSURIZATION PROBLEM. INCREASE RATE OF DSCNT, O2 MASKS DROP.

Narrative: ON DSNDING INTO TRI WHILE PASSING THROUGH 20100 MSL FELT AND SAW CABIN CLBING FULL SCALE UP (CABIN ALT APPROX 5000 FT). TOLD COPLT WHO WAS FLYING TO INCREASE RATE OF DSCNT TO 6000 FPM TO PREVIOUSLY CLRED ALT OF 7000 FT MSL. CHKED BOTH PACKS ON AND OUTFLOW VALVE SHOWED FULLY CLOSED. AS AIRPLANE PASSED THROUGH 14000+ CABIN REACHED 14000 FT AND O2 MASKS DROPPED IN PAX CABIN. 1 MIN LATER WE WERE BELOW 10000 FT AND MADE PA FOR PAX TO TAKE OFF O2 MASKS. LATER FLT ATTENDANT SAID THEY HEARD LOUD HISSING NOISE AND FELT CABIN FLOOR MOVE UNDER THEIR FT IN AFT CABIN. ALSO SAID THEY HAD TO TELL EACH PAX INDIVIDUALLY TO PUT MASK ON BECAUSE NO PAX PUT THEM ON WHEN THEY DROPPED. POST-FLT LOOKED FOR RUPTURED DUCTS BUT COULD NOT FIND ANY. CALLED MAINT COORDINATOR LATER. THEY SAID THEY HAD REPLACED THE OUTFLOW VALVE. SINCE CABIN CLBED APPROX 5000+ FPM WOULD HAVE BEEN A HANDFUL AT HIGHER ALT WITHOUT DSCNT CLRNC ON BUSY JETWAY OR ON FULL AIRPLANE WITH PAX NOT PUTTING MASKS ON SINCE THERE WAS ONLY 21 PAX. IN THIS CASE MORE OR LESS ROUTINE.

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.