Narrative:

I removed and replaced the plenum. The plenum I removed did not have a diffuser as part of the assembly. The plenum I ordered from stock did not have a diffuser assembly. The maintenance manual referred to the part as a plenum/diffuser assembly. The plenum had a serviceable tag. I thought the plenum I had received from stock was a complete assembly and I installed it in the aircraft. There was no indication that I had an incomplete assembly. The part from stock was identical to the part I removed from the aircraft. The part numbers were identical and there was a serviceable tag attached. The only way I could have avoided this situation was if I had prior knowledge of the assembly. To avoid this in future maintenance included a notice on the computer parts order page that states if ordering a plenum; to order a diffuser also. I would prefer the plenum and diffuser be assembled prior to going into stores and have a serviceable tag that covers the entire/complete assembly. Callback conversation with reporter revealed the following information: reporter stated the plenum assembly attaches to the primary and secondary heat exchangers in the air conditioning bay. The B737-700's plenums are slightly different and easier to remove and replace than the older classic B737-300/500 aircraft. The diffuser is installed with the plenum and helps to reduce the force of the air flow. Reporter stated it appears the plenum he had removed; may also have had the inner diffuser not installed and that may have been contributing to the air conditioning flight write-ups that had been plaguing that particular aircraft.

Google
 

Original NASA ASRS Text

Title: A MECHANIC REPLACING AN AIR CONDITIONING PLENUM ASSEMBLY ON A B737-700 IS LATER INFORMED HE DID NOT INSTALL THE DIFFUSER SECTION WITH THE PLENUM ASSEMBLY.

Narrative: I REMOVED AND REPLACED THE PLENUM. THE PLENUM I REMOVED DID NOT HAVE A DIFFUSER AS PART OF THE ASSEMBLY. THE PLENUM I ORDERED FROM STOCK DID NOT HAVE A DIFFUSER ASSEMBLY. THE MAINT MANUAL REFERRED TO THE PART AS A PLENUM/DIFFUSER ASSEMBLY. THE PLENUM HAD A SERVICEABLE TAG. I THOUGHT THE PLENUM I HAD RECEIVED FROM STOCK WAS A COMPLETE ASSEMBLY AND I INSTALLED IT IN THE ACFT. THERE WAS NO INDICATION THAT I HAD AN INCOMPLETE ASSEMBLY. THE PART FROM STOCK WAS IDENTICAL TO THE PART I REMOVED FROM THE ACFT. THE PART NUMBERS WERE IDENTICAL AND THERE WAS A SERVICEABLE TAG ATTACHED. THE ONLY WAY I COULD HAVE AVOIDED THIS SITUATION WAS IF I HAD PRIOR KNOWLEDGE OF THE ASSEMBLY. TO AVOID THIS IN FUTURE MAINT INCLUDED A NOTICE ON THE COMPUTER PARTS ORDER PAGE THAT STATES IF ORDERING A PLENUM; TO ORDER A DIFFUSER ALSO. I WOULD PREFER THE PLENUM AND DIFFUSER BE ASSEMBLED PRIOR TO GOING INTO STORES AND HAVE A SERVICEABLE TAG THAT COVERS THE ENTIRE/COMPLETE ASSEMBLY. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: REPORTER STATED THE PLENUM ASSEMBLY ATTACHES TO THE PRIMARY AND SECONDARY HEAT EXCHANGERS IN THE AIR CONDITIONING BAY. THE B737-700'S PLENUMS ARE SLIGHTLY DIFFERENT AND EASIER TO REMOVE AND REPLACE THAN THE OLDER CLASSIC B737-300/500 ACFT. THE DIFFUSER IS INSTALLED WITH THE PLENUM AND HELPS TO REDUCE THE FORCE OF THE AIR FLOW. REPORTER STATED IT APPEARS THE PLENUM HE HAD REMOVED; MAY ALSO HAVE HAD THE INNER DIFFUSER NOT INSTALLED AND THAT MAY HAVE BEEN CONTRIBUTING TO THE AIR CONDITIONING FLIGHT WRITE-UPS THAT HAD BEEN PLAGUING THAT PARTICULAR ACFT.

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.