Narrative:

Dec/08; I went to aircraft X for a write-up stating that automatic mode was inoperative. I deferred the automatic mode using MEL 21-16. I had another mechanic go get the plugs to plug the tube and valve. When he got back; he gave me the plug for the valve with a plug in it; so I assumed it was the plug for the tube. Plane made an emergency landing and they changed the MEL. Flight flew back to ZZZ; failed a vacuum check and plug was discovered. Changed bad plug; changed MEL back to 21-16. The cause was the plug being installed in the plug and I had never performed this task before. Also; the end of the plug comes apart if the other plug is not installed. You could install the 2 plugs in the aft avionics so there is no confusion. Or you could make pressurization MEL's rii or have a verification check. Callback conversation with reporter revealed the following information: reporter stated that part of the MEL procedure to defer the automatic mode selector for the cabin pressurization system; requires the cabin high pressure line to the electro-pneumatic outflow valve be disconnected at the valve and capped with a metal fitting that also has a metal center plug. Reporter stated his carrier has a kit to do this; but the cap he was given from another mechanic was a cap with a plastic center plug. The plastic center plug is not designed or expected to hold back the cabin high pressure in the line that was disconnected at the outflow valve. Reporter stated the plastic center came out of the metal fitting; causing a pressurization problem and an emergency landing of the emb-145LR.

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Original NASA ASRS Text

Title: While performing a maintenance MEL procedure for deferring the cabin pressurization automatic mode on an EMB-145LR aircraft; Mechanic reports he installed the wrong type of cap on a cabin pressure line.

Narrative: Dec/08; I went to Aircraft X for a write-up stating that automatic mode was inoperative. I deferred the automatic mode using MEL 21-16. I had another Mechanic go get the plugs to plug the tube and valve. When he got back; he gave me the plug for the valve with a plug in it; so I assumed it was the plug for the tube. Plane made an emergency landing and they changed the MEL. Flight flew back to ZZZ; failed a vacuum check and plug was discovered. Changed bad plug; changed MEL back to 21-16. The cause was the plug being installed in the plug and I had never performed this task before. Also; the end of the plug comes apart if the other plug is not installed. You could install the 2 plugs in the aft avionics so there is no confusion. Or you could make pressurization MEL's RII or have a verification check. Callback conversation with Reporter revealed the following information: Reporter stated that part of the MEL procedure to defer the Automatic Mode Selector for the cabin pressurization system; requires the cabin high pressure line to the electro-pneumatic outflow valve be disconnected at the valve and capped with a metal fitting that also has a metal center plug. Reporter stated his carrier has a kit to do this; but the cap he was given from another mechanic was a cap with a plastic center plug. The plastic center plug is not designed or expected to hold back the cabin high pressure in the line that was disconnected at the outflow valve. Reporter stated the plastic center came out of the metal fitting; causing a pressurization problem and an emergency landing of the EMB-145LR.

Data retrieved from NASA's ASRS site as of May 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.