DC9-50 crew was not able to control cabin altitude and made a rapid descent to 10000 ft.

Attributes
ACN	560236
Time
Date	200202
Day	Thu
Local Time Of Day	1801 To 2400
Place
State Reference	OH
Altitude	msl single value : 33000
Environment
Flight Conditions	VMC
Light	Night
Aircraft 1
Controlling Facilities	artcc : zid.artcc
Operator	common carrier : air carrier
Make Model Name	DC-9 50
Operating Under FAR Part	Part 121
Navigation In Use	other vortac
Flight Phase	cruise : level
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : flight engineer pilot : atp
Experience	flight time last 90 days : 200 flight time total : 11000 flight time type : 6000
ASRS Report	560236
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : instrument pilot : multi engine pilot : commercial
Events
Anomaly	aircraft equipment problem : critical other anomaly other
Independent Detector	aircraft equipment other aircraft equipment : cabin pressure annunciator light high alt warning horn. oxygen ma other flight crewa other flight crewb
Resolutory Action	controller : issued new clearance controller : provided flight assist other
Consequence	other other
Supplementary
Problem Areas	Aircraft
Primary Problem	Aircraft

Narrative:

Uneventful climb to FL330. Pressurization system seemed to be operating normally. Noticed right air conditioning temperature higher than normal. Made adjustments to 'balance' temperature with left air conditioning system. Short time later, cabin pressure annunciator light illuminated. Confirmed cabin pressure indicating 10000 ft. Began immediate descent with immediate coordination with ATC while first officer accomplished cabin pressure loss/rapid descent checklist. Noted pressurization outflow valve already indicated full closed. Cabin oxygen masks deployed automatically at beginning of descent. After leveloff at 10000 ft, communicated with flight attendant to confirm status of cabin. No further problems indicated. Contacted dispatch. Confirmed adequate fuel to continue to destination at 10000 ft with applicable reserves. At 10000 ft, right air conditioning was normally functional. Suspect higher than normal temperature at FL330 indicated momentary loss of right pack, allowing slow cabin climb. No explanation for more pronounced indications, ie, rapid cabin climb, ears popping, etc.

Original NASA ASRS Text

Title: DC9-50 CREW WAS NOT ABLE TO CTL CABIN ALT AND MADE A RAPID DSCNT TO 10000 FT.

Narrative: UNEVENTFUL CLB TO FL330. PRESSURIZATION SYS SEEMED TO BE OPERATING NORMALLY. NOTICED R AIR CONDITIONING TEMP HIGHER THAN NORMAL. MADE ADJUSTMENTS TO 'BAL' TEMP WITH L AIR CONDITIONING SYS. SHORT TIME LATER, CABIN PRESSURE ANNUNCIATOR LIGHT ILLUMINATED. CONFIRMED CABIN PRESSURE INDICATING 10000 FT. BEGAN IMMEDIATE DSCNT WITH IMMEDIATE COORD WITH ATC WHILE FO ACCOMPLISHED CABIN PRESSURE LOSS/RAPID DSCNT CHKLIST. NOTED PRESSURIZATION OUTFLOW VALVE ALREADY INDICATED FULL CLOSED. CABIN OXYGEN MASKS DEPLOYED AUTOMATICALLY AT BEGINNING OF DSCNT. AFTER LEVELOFF AT 10000 FT, COMMUNICATED WITH FLT ATTENDANT TO CONFIRM STATUS OF CABIN. NO FURTHER PROBS INDICATED. CONTACTED DISPATCH. CONFIRMED ADEQUATE FUEL TO CONTINUE TO DEST AT 10000 FT WITH APPLICABLE RESERVES. AT 10000 FT, R AIR CONDITIONING WAS NORMALLY FUNCTIONAL. SUSPECT HIGHER THAN NORMAL TEMP AT FL330 INDICATED MOMENTARY LOSS OF R PACK, ALLOWING SLOW CABIN CLB. NO EXPLANATION FOR MORE PRONOUNCED INDICATIONS, IE, RAPID CABIN CLB, EARS POPPING, ETC.

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.