Both engine bleed valves of a B757 tripped at FL330 with engine anti ice on causing the cabin altitu...

Narrative:

Cruising at FL370 center gave us a descent to FL330. At FL330 we entered a cloud layer where the static air temperature was -38 degrees C (icing conditions). We turned on both engine anti-ice switches. About 30 seconds after we turned on both engine anti-ice switches; we received an EICAS message and aural warning. I happened to see the right engine 'bleed' light illuminate on the overhead air conditioning panel. Then; the right engine bleed valve 'off' light illuminated and the 'bleed' light extinguished. The EICAS message showed 'right engine bleed off' so the captain accomplished the 'right engine bleed off' checklist. The checklist asks if engine anti-ice is necessary; yes. The checklist configures the air conditioning panel as follows for use in icing conditions: right engine bleed valve 'close;' right air conditioning pack 'off;' isolation valve 'on;' left engine bleed valve 'open;' left air conditioning pack 'on.' we configured all switches per the checklist. Just a few mins after accomplishing the checklist; the cockpit noise level decreased (airflow) and my ears felt a pressure change inside the airplane. I looked up at the air conditioning panel to see that now the left engine bleed valve 'off' light was illuminated (no pressurization) and the cabin pressurization rate of climb was climbing at 2000 FPM. There was no time to figure out this very unusual situation so we asked for an immediate descent from center. They gave us FL240; but we asked for an altitude of 10000 ft and they gave it to us. I used speed brakes and maximum airspeed to descend to 10000 ft. As we descended; I noticed that we were no longer in the cloud layer so I turned off both engine anti-ice switches. The captain then tried to get one of the engine bleed valves back; so he opened the right bleed valve and it worked. We now had pressurization; but were not very confident with our equipment. We decided to continue our descent to 10000 ft since we were only 100 mi or so from ZZZ and had plenty of fuel. We landed uneventfully.

Original NASA ASRS Text

Title: BOTH ENG BLEED VALVES OF A B757 TRIPPED AT FL330 WITH ENG ANTI ICE ON CAUSING THE CABIN ALT TO CLB. AN EMER DSCNT WAS BEGUN. WHEN CLEAR OF CLOUDS; ENG ANTI ICE WAS TURNED OFF AND PRESSURIZATION RETURNED.

Narrative: CRUISING AT FL370 CTR GAVE US A DSCNT TO FL330. AT FL330 WE ENTERED A CLOUD LAYER WHERE THE STATIC AIR TEMP WAS -38 DEGS C (ICING CONDITIONS). WE TURNED ON BOTH ENG ANTI-ICE SWITCHES. ABOUT 30 SECONDS AFTER WE TURNED ON BOTH ENG ANTI-ICE SWITCHES; WE RECEIVED AN EICAS MESSAGE AND AURAL WARNING. I HAPPENED TO SEE THE R ENG 'BLEED' LIGHT ILLUMINATE ON THE OVERHEAD AIR CONDITIONING PANEL. THEN; THE R ENG BLEED VALVE 'OFF' LIGHT ILLUMINATED AND THE 'BLEED' LIGHT EXTINGUISHED. THE EICAS MESSAGE SHOWED 'R ENG BLEED OFF' SO THE CAPT ACCOMPLISHED THE 'R ENG BLEED OFF' CHKLIST. THE CHKLIST ASKS IF ENG ANTI-ICE IS NECESSARY; YES. THE CHKLIST CONFIGURES THE AIR CONDITIONING PANEL AS FOLLOWS FOR USE IN ICING CONDITIONS: R ENG BLEED VALVE 'CLOSE;' R AIR CONDITIONING PACK 'OFF;' ISOLATION VALVE 'ON;' L ENG BLEED VALVE 'OPEN;' L AIR CONDITIONING PACK 'ON.' WE CONFIGURED ALL SWITCHES PER THE CHKLIST. JUST A FEW MINS AFTER ACCOMPLISHING THE CHKLIST; THE COCKPIT NOISE LEVEL DECREASED (AIRFLOW) AND MY EARS FELT A PRESSURE CHANGE INSIDE THE AIRPLANE. I LOOKED UP AT THE AIR CONDITIONING PANEL TO SEE THAT NOW THE L ENG BLEED VALVE 'OFF' LIGHT WAS ILLUMINATED (NO PRESSURIZATION) AND THE CABIN PRESSURIZATION RATE OF CLB WAS CLBING AT 2000 FPM. THERE WAS NO TIME TO FIGURE OUT THIS VERY UNUSUAL SITUATION SO WE ASKED FOR AN IMMEDIATE DSCNT FROM CTR. THEY GAVE US FL240; BUT WE ASKED FOR AN ALT OF 10000 FT AND THEY GAVE IT TO US. I USED SPD BRAKES AND MAX AIRSPD TO DSND TO 10000 FT. AS WE DSNDED; I NOTICED THAT WE WERE NO LONGER IN THE CLOUD LAYER SO I TURNED OFF BOTH ENG ANTI-ICE SWITCHES. THE CAPT THEN TRIED TO GET ONE OF THE ENG BLEED VALVES BACK; SO HE OPENED THE R BLEED VALVE AND IT WORKED. WE NOW HAD PRESSURIZATION; BUT WERE NOT VERY CONFIDENT WITH OUR EQUIP. WE DECIDED TO CONTINUE OUR DSCNT TO 10000 FT SINCE WE WERE ONLY 100 MI OR SO FROM ZZZ AND HAD PLENTY OF FUEL. WE LANDED UNEVENTFULLY.

Data retrieved from NASA's ASRS site as of May 2009 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.

Attributes
ACN	798405
Time
Date	200807
Local Time Of Day	1801 To 2400
Place
Locale Reference	airport : zzz.airport
State Reference	US
Altitude	msl single value : 33000
Environment
Flight Conditions	IMC
Weather Elements	Ice
Light	Night
Aircraft 1
Controlling Facilities	artcc : zzz.artcc
Operator	common carrier : air carrier
Make Model Name	B757 Undifferentiated or Other Model
Operating Under FAR Part	Part 121
Flight Phase	cruise : level
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : atp pilot : flight engineer pilot : private
Experience	flight time last 90 days : 225 flight time total : 12000 flight time type : 8000
ASRS Report	798405
Events
Anomaly	aircraft equipment problem : critical
Independent Detector	other flight crewa
Resolutory Action	flight crew : overcame equipment problem flight crew : exited adverse environment
Supplementary
Problem Areas	Aircraft
Primary Problem	Aircraft

Both engine bleed valves of a B757 tripped at FL330 with engine anti ice on causing the cabin altitude to climb. An emergency descent was begun. When clear of clouds; engine anti ice was turned off and pressurization returned.