Date: 201208
Local time of day: 1801-2400
Location: ZZZ.Airport, US
Flight conditions: IMC
Light: Night
Aircraft: B737-800
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Ferry / Re-Positioning
Flight phase: Cruise
Airspace: Class A ZZZ
ATC / advisory: Center ZZZ
Aircraft component: Pneumatic Valve/Bleed Valve
Component problem: Malfunctioning
Reporter organization: Air Carrier
Reporter function: Pilot Flying; First Officer
Human factors: Workload; Training / Qualification; Time Pressure; Situational Awareness; Distraction
Second reporter function: Captain; Pilot Not Flying
Anomaly: Aircraft Equipment Problem Critical; Deviation / Discrepancy - Procedural Maintenance; Deviation / Discrepancy - Procedural Published Material / Policy; Inflight Event / Encounter Weather / Turbulence
Detector: Automation Aircraft Other Automation; Person Flight Crew
When detected: In-flight
Result: Flight Crew Took Evasive Action; Flight Crew FLC complied w / Automation / Advisory; General Declared Emergency; General Maintenance Action
Contributing factors: Company Policy; Procedure; Aircraft
Primary problem: Aircraft

Narrative: I was the pilot flying with no passengers onboard and 6 total crew. Because I was a low-time in type pilot; the Captain did the takeoff since it was a special airport; but I became the pilot flying after completing the After Takeoff checklist. We had experienced a 7 hour delay on the ground because the aircraft arrived with a Left Bleed Trip Off write up. The inbound crew had the Left Bleed Trip Off several times; and Maintenance spent a long time troubleshooting. They replaced two parts one of which was the temperature sensor. After they completed an engine run and testing; we were given the aircraft to fly. The flight started uneventful. We noticed during climb out (don't recall altitude) there was a split in duct pressure. Right duct was about 37 PSI and the left duct was about 27 PSI. During our climb up to FL360; we experienced a Left Bleed Trip Off at FL330. We decided to level off at FL340. I flew the aircraft and had the radios and the Captain worked the Bleed Trip Off QRH. We pressed the trip reset per the QRH and the light extinguished. Both ducts pressures were approximately 33 PSI. After maybe 5 seconds; the left duct dropped to about 27 PSI again and then dropped to 22 PSI followed by a Left Bleed Trip Off again. We continued the QRH and turned off the Left Pack. We decided to continue to our filed destination. We were filed at FL380 and decided to stay at FL340 because we had the fuel and felt it would be better in case we needed to descend due to a pressurization problem. The ride was a bit bumpy so we climbed to FL360. A short while later; we climbed to FL380 to get on top of a little layer we could see that was painting mostly green on radar. It was dark out and difficult to determine if we would be able to avoid the layer. As we approached the weather; we flew into a little cloud layer. The temperature I think was -54 C and did not require engine anti-ice. We were almost through the green depicted area on the radar when Center gave us a descent from FL380-360. We were IMC and in a descent so we placed the engine anti-ice on. At this point I don't recall if the incident occurred during the descent or not but I believed we had leveled off at FL360 before the event occurred. I was briefing the arrival and approach because we were about 5 minutes from top of descent. Very shortly thereafter we experienced a Master Caution for air conditioning. I looked up and saw we now had a Right Bleed Trip Off as well. I looked at the cabin altitude indicator and saw the cabin was slowly (about 500 FPM) climbing. The Captain yelled out the memory items and we both donned our oxygen masks and tried to communicate. The seat belt sign was already on. I became distracted initially because the Captain was having difficulty establishing communications and trying to pull out the QRH which he appeared to be fumbling with. At the same time; the flight attendants were in the cabin and were trying to call through the interphone which neither one of us responded to. After my initial distraction; I called Center and stated we needed an emergency descent due to loss of pressurization. We were cleared to 11;000 FT and the Captain dialed 27;400 FT into the altitude window and then went back to trying to communicate with me and do the QRH at the same time. I could see the Captain was struggling with those two tasks so I clicked off the autopilot and autothrottle; pulled the throttles to idle and begin an immediate descent. I dialed in 11;000 in the altitude window and selected level change and ran the speed window up to the barber poll and descended near the barber poll. I missed getting the speedbrakes out and Captain pointed to them and I went to full in flight deployment of speedbrakes. The Captain was working through the QRH but it seemed to be taking a long time. Since we had just run the Bleed Trip Off checklist; I reached up (passing FL260) and pressed the trip reset button. The Right Bleed Trip Off remained illuminated but the Left Bleed Trip Off extinguished. I looked at the cabin altitude indicator and saw the cabin was beginning to descend. The Left Bleed Trip Off tripped again after maybe 30 seconds but it bought us a little more time to get down. The cabin warning horn sounded and I silenced the horn. The aircraft caught up with the cabin at approximately 14;500 FT. We continued the descent to 10;000 FT and at some point during the dive; the Captain declared an emergency with ATC and stated fuel and souls on board. The passenger masks were manually deployed per the QRH procedure. At 10;000 FT we took off our masks and I told the Captain to check on the flight attendants. I also asked for an early descent from ATC because we were unpressurized and I wanted to restrict the descent to 500 FT per minute. We proceeded to a fix on the ILS and landed uneventfully. After taxiing into the gate; the Captain entered the items in the maintenance logbook and we discussed the issue with the mechanics. I was through but the Captain was still scheduled for a delayed flight that night. I advised the Captain to call the Duty Manager and have himself assessed before continuing following our incident.


Second narrative: [Narrative 2 contained no additional information]


Synopsis: A B737-800 with an engine bleed air trip history was at FL330 when the Left Bleed tripped. To get over weather; they climbed to FL380 where there second bleed tripped; so an emergency was declared and the flight descended to 10;000 FT with crew and passenger oxygen in used.