Narrative:

I was one of the mechanics working the air conditioning bay checks when apparently a blocking plug, used to isolate the system, that I installed was not removed. In order to leak check the air conditioning, bay caps and plates have to be installed to keep the air in the system. We cannot run the APU in the hangar and can't wait until the last day of the 'C' check on the engine run to do an initial leak check. On heavy 'C' checks, a card used to be issued. This card tells you to install numerous blocking plates in the air conditioning bay plus 4 blocking caps in the aft stair area. This will allow the system to hold shop air without dumping it out the purge valves. On the aircraft in question, I installed blocking plates in the air conditioning bay and installed the 4 blocking caps in the aft stairs. This set-up is typically turned over to the next shift where they can accomplish the leak check and reassemble the system. However, on this aircraft the fitting in the tail was too tight. Any pressure at all usually breaks the 'T' fitting, so I moved the cap upstream about 20 inches and installed a cap, still in line of sight with a large yellow tag that read 'blocking plate installed.' when I came in the aircraft bay the air conditioning system had been sold off and the panels were closed. I remember this because I was put on a different job. The system leak checks were accomplished, blocking plates were removed and the air conditioning bay and aft stair arm were finaled by another mechanic and quality assurance.

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Original NASA ASRS Text

Title: A B727-200 WAS RELEASED FOR SVC WITH A CAPPED AIR CONDITIONING SYS PRESSURE SENSE LINE INSTALLED FOR PRESSURE TESTING ON A 'C' CHK.

Narrative: I WAS ONE OF THE MECHS WORKING THE AIR CONDITIONING BAY CHKS WHEN APPARENTLY A BLOCKING PLUG, USED TO ISOLATE THE SYS, THAT I INSTALLED WAS NOT REMOVED. IN ORDER TO LEAK CHK THE AIR CONDITIONING, BAY CAPS AND PLATES HAVE TO BE INSTALLED TO KEEP THE AIR IN THE SYS. WE CANNOT RUN THE APU IN THE HANGAR AND CAN'T WAIT UNTIL THE LAST DAY OF THE 'C' CHK ON THE ENG RUN TO DO AN INITIAL LEAK CHK. ON HVY 'C' CHKS, A CARD USED TO BE ISSUED. THIS CARD TELLS YOU TO INSTALL NUMEROUS BLOCKING PLATES IN THE AIR CONDITIONING BAY PLUS 4 BLOCKING CAPS IN THE AFT STAIR AREA. THIS WILL ALLOW THE SYS TO HOLD SHOP AIR WITHOUT DUMPING IT OUT THE PURGE VALVES. ON THE ACFT IN QUESTION, I INSTALLED BLOCKING PLATES IN THE AIR CONDITIONING BAY AND INSTALLED THE 4 BLOCKING CAPS IN THE AFT STAIRS. THIS SET-UP IS TYPICALLY TURNED OVER TO THE NEXT SHIFT WHERE THEY CAN ACCOMPLISH THE LEAK CHK AND REASSEMBLE THE SYS. HOWEVER, ON THIS ACFT THE FITTING IN THE TAIL WAS TOO TIGHT. ANY PRESSURE AT ALL USUALLY BREAKS THE 'T' FITTING, SO I MOVED THE CAP UPSTREAM ABOUT 20 INCHES AND INSTALLED A CAP, STILL IN LINE OF SIGHT WITH A LARGE YELLOW TAG THAT READ 'BLOCKING PLATE INSTALLED.' WHEN I CAME IN THE ACFT BAY THE AIR CONDITIONING SYS HAD BEEN SOLD OFF AND THE PANELS WERE CLOSED. I REMEMBER THIS BECAUSE I WAS PUT ON A DIFFERENT JOB. THE SYS LEAK CHKS WERE ACCOMPLISHED, BLOCKING PLATES WERE REMOVED AND THE AIR CONDITIONING BAY AND AFT STAIR ARM WERE FINALED BY ANOTHER MECH AND QUALITY ASSURANCE.

Data retrieved from NASA's ASRS site as of July 2007 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.