B757 SUFFERS FAILURE OF BOTH LEFT AND RIGHT ENGINE BLEED VALVES WHILE OPERATING IN VISIBLE MOISTURE RESULTING IN A LOSS OF PRESSURIZATION AND ENGINE ANTI-ICE. UPON DESCENT AND EXITING ICING CONDITIONS BLEED AIR AND PRESSURIZATION WERE RESTORED.

Narrative

APCHING TOP OF DSCNT; FLT IS IN VISIBLE MOISTURE WITH STATIC AIR TEMP -38 DEGS C; SO L AND R ENG ANTI-ICE IS TURNED ON. A FEW MINS LATER; THE R ENG BLEED VALVE OVERHEAD ANNUNCIATOR AND L ENG BLEED VALVE EICAS MESSAGE ILLUMINATED. AS PLT MONITORING OPENS QRH; THE BLEED VALVE ANNUNCIATOR AND EICAS MESSAGES EXTINGUISH BUT THE R ENG BLEED TURNS OFF; R PACK TURNS OFF AND R ENG BLEED OFF EICAS MESSAGE ILLUMINATES. PLT MONITORING AND PF ACCOMPLISH R ENG BLEED OFF CHKLIST RESULTING IN L BLEED SUPPLYING PNEUMATICS FOR L PACK AND L AND R ENG ANTI-ICE. A FEW MINS LATER; THE L BLEED TURNS OFF RESULTING IN BOTH PACKS OFF; NO ENG ANTI-ICE AND THE CABIN DEPRESSURIZING. AS THE CREW RECOGNIZED THE DUAL BLEED FAILURE AND CABIN ALT CLBING; ATC CLRED US TO FL240 AND PF INITIATED DSCNT. PLT MONITORING ACKNOWLEDGED THE CLRNC AND REQUESTED LOWER ASAP DUE TO ACFT PRESSURIZATION PROB. ATC ASKED HOW LOW AND PLT MONITORING RESPONDED '10000 FT.' ATC CLRED TO A HDG OFF OF THE ARR AND DSCNT TO 10000 FT. BELOW FL330 ICING CONDITIONS DID NOT EXIST SO L AND R ENG ANTI-ICE WAS TURNED OFF. PLT MONITORING TURNED ON R ENG BLEED VALVE AND DUCT PRESSURE RETURNED. PLT MONITORING TURNED ON R PACK AND ACFT CABIN BEGAN TO PRESSURIZE NORMALLY AT APPROX FL280. CABIN ALT STAYED BELOW 10000 FT. NO CABIN ALT WARNINGS ACTIVATED. PAX OXYGEN SYS DID NOT ACTIVATE. PLT MONITORING RPTED TO ATC THAT PRESSURIZATION HAD STABILIZED BUT REQUESTED ARR TO ZZZ AT 10000 FT AS A PRECAUTIONARY MEASURE. NO DECLARATION OF EMER WAS MADE AS IT WAS DEEMED NOT NECESSARY GIVEN THE CIRCUMSTANCES. NORMAL APCH AND LNDG ACCOMPLISHED. THOROUGH LOGBOOK ENTRY WAS MADE DESCRIBING THE ENG BLEED/PRESSURIZATION INCIDENT AFTER ACTIVATION OF ENG ANTI-ICE. COMPANY MECHS MET THE FLT AND RECEIVED FULL DEBRIEF OF THE INCIDENT. FOLLOW-UP WITH MAINT REVEALED THAT THIS WAS THE SECOND INCIDENT OF A DUAL BLEED TRIP FOR THIS ACFT. THE INCIDENT WAS DUE TO OVERHEAT CAUSED BY R ENG ANTI-ICE SYS.