B737 crew was forced to make an emergency descent when both packs tripped off.

Attributes
ACN	415039
Time
Date	199809
Day	Tue
Local Time Of Day	1801 To 2400
Place
Locale Reference	atc facility : gjt
State Reference	CO
Altitude	msl bound lower : 31000 msl bound upper : 31000
Environment
Flight Conditions	VMC
Light	Night
Aircraft 1
Controlling Facilities	artcc : zdv tower : tlh
Operator	common carrier : air carrier
Make Model Name	B737-300
Operating Under FAR Part	Part 121
Navigation In Use	Other Other
Flight Phase	cruise other other other
Route In Use	enroute : on vectors
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : instrument pilot : flight engineer pilot : commercial pilot : atp
Experience	flight time last 90 days : 200 flight time total : 9000 flight time type : 2000
ASRS Report	415039
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : commercial pilot : instrument
Events
Anomaly	aircraft equipment problem : critical other anomaly other
Independent Detector	other flight crewa
Resolutory Action	flight crew : declared emergency other
Consequence	Other
Supplementary
Primary Problem	Aircraft

Narrative:

Air carrier flight XXX den to sjc on sep/xa/98 on a B737-300 aircraft. I was flying as captain. We leveled off at FL310. The first indication of a malfunction was the illumination of the #1 pack trip off light. We accomplished checklist and light went out. 1 min later light illuminated again, accomplished checklist and left #1 pack off. We requested a lower altitude. 5 mins later #2 pack trip off light illuminated and we lost the pressurization system. Accomplished checklist and descended to 12000 ft. Regained 1 pack operation. Contacted air carrier maintenance and air carrier dispatch. Mechanically accomplished everything possible and our best option was to return to den. Requested a safe route (10000 ft) from ZDV and air carrier dispatch. Landed safely at approximately XX45.

Original NASA ASRS Text

Title: B737 CREW WAS FORCED TO MAKE AN EMER DSCNT WHEN BOTH PACKS TRIPPED OFF.

Narrative: ACR FLT XXX DEN TO SJC ON SEP/XA/98 ON A B737-300 ACFT. I WAS FLYING AS CAPT. WE LEVELED OFF AT FL310. THE FIRST INDICATION OF A MALFUNCTION WAS THE ILLUMINATION OF THE #1 PACK TRIP OFF LIGHT. WE ACCOMPLISHED CHKLIST AND LIGHT WENT OUT. 1 MIN LATER LIGHT ILLUMINATED AGAIN, ACCOMPLISHED CHKLIST AND LEFT #1 PACK OFF. WE REQUESTED A LOWER ALT. 5 MINS LATER #2 PACK TRIP OFF LIGHT ILLUMINATED AND WE LOST THE PRESSURIZATION SYS. ACCOMPLISHED CHKLIST AND DSNDED TO 12000 FT. REGAINED 1 PACK OP. CONTACTED ACR MAINT AND ACR DISPATCH. MECHANICALLY ACCOMPLISHED EVERYTHING POSSIBLE AND OUR BEST OPTION WAS TO RETURN TO DEN. REQUESTED A SAFE RTE (10000 FT) FROM ZDV AND ACR DISPATCH. LANDED SAFELY AT APPROX XX45.

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.