Narrative:

I was asked to help change out a pre-cooler control valve as per request of maintenance control. Chapter 36 history was researched and it was said that we have been experiencing a larger failure rate with these valves on -700's. Talked to the crew while I started opening #2 engine. We changed the pre-cooler control valve and a sense line. When actuating the valve; I could hear a diaphragm that sounded damaged and didn't feel right. Confident that this was at fault; we closed up for engine run-up. Before pushback; we noticed engine bleed air was on MEL; so we had to open the engine again and unlock the prsov. The high stage valve was misidented as the prsov. I don't know if that valve was locked out; but I did make sure it (high stage value) was open before closing the engine again for engine run-up. This could have been prevented if a complete maintenance manual check-out of right&right of pre-cooler control valve would have been performed allowing the MEL to be cleared correctly. Also; the run-up pad had partial snow cover on it causing the aircraft to slide forward approximately 10 ft when throttles were advanced. Due to this distraction; the bleed system was not correctly isolated; had it been; this problem would have been prevented.

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Original NASA ASRS Text

Title: A B737-200 #2 ENG PNEUMATIC PRE-COOLER VALVE WAS REPLACED AND PRIOR TO ENG RUN IT WAS DISCOVERED THE HIGH PRESSURE VALVE WAS LOCKED CLOSED.

Narrative: I WAS ASKED TO HELP CHANGE OUT A PRE-COOLER CTL VALVE AS PER REQUEST OF MAINT CTL. CHAPTER 36 HISTORY WAS RESEARCHED AND IT WAS SAID THAT WE HAVE BEEN EXPERIENCING A LARGER FAILURE RATE WITH THESE VALVES ON -700'S. TALKED TO THE CREW WHILE I STARTED OPENING #2 ENG. WE CHANGED THE PRE-COOLER CTL VALVE AND A SENSE LINE. WHEN ACTUATING THE VALVE; I COULD HEAR A DIAPHRAGM THAT SOUNDED DAMAGED AND DIDN'T FEEL RIGHT. CONFIDENT THAT THIS WAS AT FAULT; WE CLOSED UP FOR ENG RUN-UP. BEFORE PUSHBACK; WE NOTICED ENG BLEED AIR WAS ON MEL; SO WE HAD TO OPEN THE ENG AGAIN AND UNLOCK THE PRSOV. THE HIGH STAGE VALVE WAS MISIDENTED AS THE PRSOV. I DON'T KNOW IF THAT VALVE WAS LOCKED OUT; BUT I DID MAKE SURE IT (HIGH STAGE VALUE) WAS OPEN BEFORE CLOSING THE ENG AGAIN FOR ENG RUN-UP. THIS COULD HAVE BEEN PREVENTED IF A COMPLETE MAINT MANUAL CHK-OUT OF R&R OF PRE-COOLER CTL VALVE WOULD HAVE BEEN PERFORMED ALLOWING THE MEL TO BE CLRED CORRECTLY. ALSO; THE RUN-UP PAD HAD PARTIAL SNOW COVER ON IT CAUSING THE ACFT TO SLIDE FORWARD APPROX 10 FT WHEN THROTTLES WERE ADVANCED. DUE TO THIS DISTR; THE BLEED SYS WAS NOT CORRECTLY ISOLATED; HAD IT BEEN; THIS PROB WOULD HAVE BEEN PREVENTED.

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.