Narrative:

While cruising at FL350 with the left air conditioning pack deferred inoperative; we first noticed a sudden decrease in the sound of incoming air; and immediate sensation in the ears of a change in cabin pressure as well as an EICAS indication and overhead lights of left and right engine bleed air and right pack off indication. After doublechking we were getting a cabin rate of climb of approximately 700-800 FPM; we donned our oxygen masks and requested an immediate descent from ATC. Captain made a PA announcement for flight attendants to take their seats and turned on the seatbelt sign. ATC cleared us to descend as needed. We reported we were starting a 90 degree l-hand turn for traffic avoidance; however; ATC instructed for us to remain on course; which we did. In the meantime the first officer used the qrc to prepare for an even faster descent in case we needed it. He also began to reset the pneumatics panel in an attempt to regain control of the pressurization. The actions resulted in a recovery of the bleed air and the right pack and subsequent solution to the pressurization problem. The cabin stabilized and we advised ATC that we could level off at FL250. We advised ATC that we would continue on course. At that time we removed our oxygen masks. After getting a phone patch and talking with dispatch and maintenance we all agreed to continue to lga and monitor the situation. After about 15-20 mins we began to experience a repeat of the same problem. This time we asked ATC for a descent to 10000 ft. During the descent; the first officer was once again able to regain control of the bleeds and right pack. Also during the descent we received a call from the flight attendant that a lady had had an anxiety attack and were attending to her with oxygen. Captain asked to be kept informed. Approximately 15 mins later and on the STAR into lga the problem occurred for a third time. This time; upon regaining control of the pressurization; the duct pressure began fluctuating between 30-60 psi. We started the APU and opened the APU bleed valve and closed the engine bleed valves and the system stabilized and no further problems were encountered. The flight attendant called and requested that medical personnel be called as a precaution on our arrival even though the passenger did not think she needed it. At no time did we feel the situation was an emergency but it did need immediate action to prevent that possibility. ATC granted the altitude changes immediately and at no time did the cabin altitude exceed 9000 ft as we were able to gain control of the pressurization after reach occurrence.

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Original NASA ASRS Text

Title: FLT CREW OF B757-200 DEMONSTRATE GOOD TECHNICAL SKILLS AND SYSTEM KNOWLEDGE WHILE DEALING WITH A RECURRING PRESSURIZATION PROBLEM.

Narrative: WHILE CRUISING AT FL350 WITH THE L AIR CONDITIONING PACK DEFERRED INOP; WE FIRST NOTICED A SUDDEN DECREASE IN THE SOUND OF INCOMING AIR; AND IMMEDIATE SENSATION IN THE EARS OF A CHANGE IN CABIN PRESSURE AS WELL AS AN EICAS INDICATION AND OVERHEAD LIGHTS OF L AND R ENG BLEED AIR AND R PACK OFF INDICATION. AFTER DOUBLECHKING WE WERE GETTING A CABIN RATE OF CLB OF APPROX 700-800 FPM; WE DONNED OUR OXYGEN MASKS AND REQUESTED AN IMMEDIATE DSCNT FROM ATC. CAPT MADE A PA ANNOUNCEMENT FOR FLT ATTENDANTS TO TAKE THEIR SEATS AND TURNED ON THE SEATBELT SIGN. ATC CLRED US TO DSND AS NEEDED. WE RPTED WE WERE STARTING A 90 DEG L-HAND TURN FOR TFC AVOIDANCE; HOWEVER; ATC INSTRUCTED FOR US TO REMAIN ON COURSE; WHICH WE DID. IN THE MEANTIME THE FO USED THE QRC TO PREPARE FOR AN EVEN FASTER DSCNT IN CASE WE NEEDED IT. HE ALSO BEGAN TO RESET THE PNEUMATICS PANEL IN AN ATTEMPT TO REGAIN CTL OF THE PRESSURIZATION. THE ACTIONS RESULTED IN A RECOVERY OF THE BLEED AIR AND THE R PACK AND SUBSEQUENT SOLUTION TO THE PRESSURIZATION PROB. THE CABIN STABILIZED AND WE ADVISED ATC THAT WE COULD LEVEL OFF AT FL250. WE ADVISED ATC THAT WE WOULD CONTINUE ON COURSE. AT THAT TIME WE REMOVED OUR OXYGEN MASKS. AFTER GETTING A PHONE PATCH AND TALKING WITH DISPATCH AND MAINT WE ALL AGREED TO CONTINUE TO LGA AND MONITOR THE SIT. AFTER ABOUT 15-20 MINS WE BEGAN TO EXPERIENCE A REPEAT OF THE SAME PROB. THIS TIME WE ASKED ATC FOR A DSCNT TO 10000 FT. DURING THE DSCNT; THE FO WAS ONCE AGAIN ABLE TO REGAIN CTL OF THE BLEEDS AND R PACK. ALSO DURING THE DSCNT WE RECEIVED A CALL FROM THE FLT ATTENDANT THAT A LADY HAD HAD AN ANXIETY ATTACK AND WERE ATTENDING TO HER WITH OXYGEN. CAPT ASKED TO BE KEPT INFORMED. APPROX 15 MINS LATER AND ON THE STAR INTO LGA THE PROB OCCURRED FOR A THIRD TIME. THIS TIME; UPON REGAINING CTL OF THE PRESSURIZATION; THE DUCT PRESSURE BEGAN FLUCTUATING BTWN 30-60 PSI. WE STARTED THE APU AND OPENED THE APU BLEED VALVE AND CLOSED THE ENG BLEED VALVES AND THE SYS STABILIZED AND NO FURTHER PROBS WERE ENCOUNTERED. THE FLT ATTENDANT CALLED AND REQUESTED THAT MEDICAL PERSONNEL BE CALLED AS A PRECAUTION ON OUR ARR EVEN THOUGH THE PAX DID NOT THINK SHE NEEDED IT. AT NO TIME DID WE FEEL THE SIT WAS AN EMER BUT IT DID NEED IMMEDIATE ACTION TO PREVENT THAT POSSIBILITY. ATC GRANTED THE ALT CHANGES IMMEDIATELY AND AT NO TIME DID THE CABIN ALT EXCEED 9000 FT AS WE WERE ABLE TO GAIN CTL OF THE PRESSURIZATION AFTER REACH OCCURRENCE.

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