Md-80S aircraft in cruise had loss of cabin pressure due to both packs tripping off. Wing anti ice was not on at the time and reporter captain surmised that the inlet on the bottom of the vertical stabilizer became iced up causing the pack trips.

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Attributes
ACN	404413
Time
Date	199804
Day	Mon
Local Time Of Day	0601 To 1200
Place
Locale Reference	atc facility : lit
State Reference	AR
Environment
Light	Daylight
Aircraft 1
Controlling Facilities	artcc : zme
Operator	common carrier : air carrier
Make Model Name	MD-80 Super 80
Operating Under FAR Part	Part 121
Navigation In Use	Other
Flight Phase	cruise other descent other other
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
ASRS Report	404413
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : instrument pilot : commercial
Events
Anomaly	aircraft equipment problem : critical altitude deviation : excursion from assigned altitude other anomaly other
Independent Detector	aircraft equipment other aircraft equipment : unspecified other flight crewa
Resolutory Action	flight crew : declared emergency flight crew : overcame equipment problem
Consequence	Other
Supplementary
Primary Problem	Aircraft
Air Traffic Incident	other

Narrative:

This is a follow up to a report I sent last month concerning the loss of cabin pressure we experienced. It appears that the loss of both packs at altitude was caused by not using wing anti ice at altitude. Even though we were at altitude and using engine anti ice we did not feel the need to use wing anti ice since we were in a very light cirrus layer and were not appearing to pick up ice. It appears the inlet on the bottom of the vertical stabilizer became blocked at altitude, followed by an unannunciated double pack trip and a high dive with subsequent presentation of oxygen masks to all aboard. Our mentality on use of wing anti ice sometimes has been tainted by lack of problems on other aircraft we have flown. The MD80 has a very unique problem and the use of wing anti ice can cure it. Be smart -- when using engine anti ice use wing also -- or be up to snuff on your rapid depressurization checklist. The choice is yours. I know what my choice will be. Be safe out there.

Original NASA ASRS Text

Title: MD-80S ACFT IN CRUISE HAD LOSS OF CABIN PRESSURE DUE TO BOTH PACKS TRIPPING OFF. WING ANTI ICE WAS NOT ON AT THE TIME AND RPTR CAPT SURMISED THAT THE INLET ON THE BOTTOM OF THE VERT STAB BECAME ICED UP CAUSING THE PACK TRIPS.

Narrative: THIS IS A FOLLOW UP TO A RPT I SENT LAST MONTH CONCERNING THE LOSS OF CABIN PRESSURE WE EXPERIENCED. IT APPEARS THAT THE LOSS OF BOTH PACKS AT ALT WAS CAUSED BY NOT USING WING ANTI ICE AT ALT. EVEN THOUGH WE WERE AT ALT AND USING ENG ANTI ICE WE DID NOT FEEL THE NEED TO USE WING ANTI ICE SINCE WE WERE IN A VERY LIGHT CIRRUS LAYER AND WERE NOT APPEARING TO PICK UP ICE. IT APPEARS THE INLET ON THE BOTTOM OF THE VERT STAB BECAME BLOCKED AT ALT, FOLLOWED BY AN UNANNUNCIATED DOUBLE PACK TRIP AND A HIGH DIVE WITH SUBSEQUENT PRESENTATION OF OXYGEN MASKS TO ALL ABOARD. OUR MENTALITY ON USE OF WING ANTI ICE SOMETIMES HAS BEEN TAINTED BY LACK OF PROBLEMS ON OTHER ACFT WE HAVE FLOWN. THE MD80 HAS A VERY UNIQUE PROB AND THE USE OF WING ANTI ICE CAN CURE IT. BE SMART -- WHEN USING ENG ANTI ICE USE WING ALSO -- OR BE UP TO SNUFF ON YOUR RAPID DEPRESSURIZATION CHKLIST. THE CHOICE IS YOURS. I KNOW WHAT MY CHOICE WILL BE. BE SAFE OUT THERE.

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.