Narrative:

Previous day write-up for left bleed trip off - repaired overnight. On climb (4;000); got left bleed trip off; first officer checks pressure and temps good and resets okay. Passing 10;000 got the trip again. First officer goes through checklist and it resets initially but immediately trips again. All other indications are normal. Turned left pack off per QRH. I call dispatch to evaluate avoiding icing conditions at destination. I level at FL330 vice FL390. Dispatch had no options- so I return to departure airport. Twice ATC asks if we are emergency and I say no; normal return. At FL240 on vectors; we hear the intermittent horn. We feel no ears popping or any change in pressure. I look up and see 8;000 ft on cabin altitude and 5 diff pressure. I push the power up to no affect. We look around for anything abnormal. First officer checks duct pressure 40 psi; all normal. First officer manually closes outflow valve. I see 4 diff pressure and 10;000 cabin altitude; we start emergency descent procedure. First officer declares emergency with ATC and requests 10;000 ft. ATC responds descend to 17;000 ft; traffic below. First officer says we are an emergency get them out of our way. (I'm wondering just how close the traffic is. I look at TCAS and see no one close.) I immediately step in with; declaring an emergency; cabin is depressurized; and we are descending to 10;000 ft. ATC clears us to 10;000 ft. ATC is very cooperative rest of way to landing. Cabin altitude read 10;000 ft when we leveled at 10;000. We could hear and feel the relief doors cycling. Thus at that point; I believe the cabin pressure read accurately. At one point; the diff needle blocked the cabin altitude needle at a critical time. These old dual round gages need to go away.

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Original NASA ASRS Text

Title: B737-800 Captain reports being dispatched in an aircraft which had recently been written up for a left bleed trip. During initial climb the problem reoccurs twice and the bleed valve is closed and the left pack turned off. The decision is made to return to departure airport due to destination weather and at FL240 the cabin altitude warning horn sounds and an emergency descent is commenced. A normal landing ensues.

Narrative: Previous day write-up for LEFT BLEED TRIP OFF - repaired overnight. On climb (4;000); got LEFT BLEED TRIP OFF; First Officer checks pressure and temps good and resets okay. Passing 10;000 got the trip again. First Officer goes through checklist and it resets initially but immediately trips again. All other indications are normal. Turned Left Pack OFF per QRH. I call Dispatch to evaluate avoiding icing conditions at destination. I level at FL330 vice FL390. Dispatch had no options- so I return to departure airport. Twice ATC asks if we are emergency and I say no; normal return. At FL240 on vectors; we hear the intermittent horn. We feel no ears popping or any change in pressure. I look up and see 8;000 FT on cabin altitude and 5 diff pressure. I push the power up to no affect. We look around for anything abnormal. First Officer checks duct pressure 40 PSI; all normal. First Officer manually closes outflow valve. I see 4 diff pressure and 10;000 cabin altitude; we start emergency descent procedure. First Officer declares Emergency with ATC and requests 10;000 FT. ATC responds descend to 17;000 FT; traffic below. First Officer says we are an emergency get them out of our way. (I'm wondering just how close the traffic is. I look at TCAS and see no one close.) I immediately step in with; declaring an emergency; cabin is depressurized; and we are descending to 10;000 FT. ATC clears us to 10;000 FT. ATC is very cooperative rest of way to landing. Cabin altitude read 10;000 FT when we leveled at 10;000. We could hear and feel the relief doors cycling. Thus at that point; I believe the cabin pressure read accurately. At one point; the diff needle blocked the cabin altitude needle at a critical time. These old dual round gages need to go away.

Data retrieved from NASA's ASRS site as of April 2012 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.