Loss of cabin pressurization at FL330 and emergency descent to 10000'.

Attributes
ACN	89413
Time
Date	198806
Day	Sat
Local Time Of Day	1801 To 2400
Place
Locale Reference	atc facility : cha
State Reference	TN
Altitude	msl bound lower : 10000 msl bound upper : 33000
Environment
Flight Conditions	VMC
Light	Night
Aircraft 1
Controlling Facilities	artcc : ztl
Operator	common carrier : air carrier
Make Model Name	Medium Large Transport, Low Wing, 2 Turbojet Eng
Flight Phase	cruise other
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : atp
Experience	flight time last 90 days : 100 flight time total : 6700
ASRS Report	89413
Person 2
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
Experience	flight time last 90 days : 210 flight time total : 14500
ASRS Report	89246
Events
Anomaly	aircraft equipment problem : critical
Independent Detector	aircraft equipment other aircraft equipment : unspecified other flight crewa
Resolutory Action	flight crew : declared emergency none taken : anomaly accepted none taken : unable
Consequence	Other
Supplementary
Primary Problem	Aircraft

Narrative:

At FL330 over cha, tn, both AC packs quit simultaneously. The cabin altitude started climbing quite rapidly through 10000'. O2 masks were donned and an emergency descent initiated to 10000'. Upon leveling at 10000' the packs returned to normal operation west/O being reset. All emergency checklists (QRH) were completed during descent. Cabin altitude climbed to 15000' briefly. No aircraft or personal damage was observed so we elected to land at our destination (gsp). Since both pacs operate independently of each other, the odds of both quitting at once are quite remote. I believe the AC pacs was still armed even though the switch was placed in override earlier per climb checklist. One pack shocked out and the other sensed the pressurization difference and quit to deliver more power for the engine. Supplemental information from acn 89246: the cabin pressure annunciation panel light came on. We went on O2, asked ATC for an emergency descent to 10000' MSL, which we received and descended in an emergency descent profile to 10000'.

Original NASA ASRS Text

Title: LOSS OF CABIN PRESSURIZATION AT FL330 AND EMERGENCY DESCENT TO 10000'.

Narrative: AT FL330 OVER CHA, TN, BOTH AC PACKS QUIT SIMULTANEOUSLY. THE CABIN ALT STARTED CLBING QUITE RAPIDLY THROUGH 10000'. O2 MASKS WERE DONNED AND AN EMER DSCNT INITIATED TO 10000'. UPON LEVELING AT 10000' THE PACKS RETURNED TO NORMAL OPERATION W/O BEING RESET. ALL EMER CHKLISTS (QRH) WERE COMPLETED DURING DSCNT. CABIN ALT CLBED TO 15000' BRIEFLY. NO ACFT OR PERSONAL DAMAGE WAS OBSERVED SO WE ELECTED TO LAND AT OUR DEST (GSP). SINCE BOTH PACS OPERATE INDEPENDENTLY OF EACH OTHER, THE ODDS OF BOTH QUITTING AT ONCE ARE QUITE REMOTE. I BELIEVE THE AC PACS WAS STILL ARMED EVEN THOUGH THE SWITCH WAS PLACED IN OVERRIDE EARLIER PER CLB CHKLIST. ONE PACK SHOCKED OUT AND THE OTHER SENSED THE PRESSURIZATION DIFFERENCE AND QUIT TO DELIVER MORE PWR FOR THE ENG. SUPPLEMENTAL INFO FROM ACN 89246: THE CABIN PRESSURE ANNUNCIATION PANEL LIGHT CAME ON. WE WENT ON O2, ASKED ATC FOR AN EMER DSCNT TO 10000' MSL, WHICH WE RECEIVED AND DSNDED IN AN EMER DSCNT PROFILE TO 10000'.

Data retrieved from NASA's ASRS site as of August 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.