Narrative:

I was coming back from a canceled tow; when dayshift lead told me to stop by [another gate] and help out mechanic Y on an [aircraft] return to gate call. I printed out MEL 21- 26-04 and we went thru it together. When I went thru the process of opening skin air outlet valve per MEL 21-26-04 I got confused with the instructions provided. MEL figure-a does not differentiate the [outlet valve] main door from the auxiliary door and internal valve doors. This picture only shows the handle; the on/off switch and auxiliary flap (which appears to be pointing at whole door). Also instructions are a little confusing. So I made the mistake of partially opening the main flap instead of the auxiliary flap. Then I proceeded to finish the rest of the maintenance MEL procedure. I asked mechanic Y to take a look at the MEL procedure and told him what I had done. He agreed that the MEL was confusing and agreed with what I had done. Then mechanic Y did an avionics equipment ventilation computer (aevc) test and finished paperwork. We heard on the radio that the airplane was coming back to the gate. Air turn back [due to] avionics outlet skin air valve main door was not fully closed; [causing] an avionics vent fault.then mechanic Y and I did more research involving aircraft maintenance manual (amm) 21-26-00 and task 21-26-00-040-002 that made it very clear on position required of main/auxiliary [outlet valve] flaps and deactivation procedure. We re-accomplished deactivation procedure in accordance with MEL and amm 21-26-00 and task 21-26-00-040-002; re-accomplished the avionics equipment ventilation computer (aevc) test and paperwork. Suggest better labeling of figures/drawings and procedures in MEL 21-26-04 and more classroom/hands-on training.

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Original NASA ASRS Text

Title: Two Technicians report about misinterpreting an MEL 21-26-04 Maintenance procedure for deferring an A320 aircraft's skin air outlet valve in the closed position. Inadequate MEL Maintenance illustrations lead them to believe the skin valve's main door; not the smaller auxiliary door; should be left partially opened.

Narrative: I was coming back from a canceled tow; when Dayshift Lead told me to stop by [another Gate] and help out Mechanic Y on an [aircraft] return to gate call. I printed out MEL 21- 26-04 and we went thru it together. When I went thru the process of opening skin air outlet valve per MEL 21-26-04 I got confused with the instructions provided. MEL Figure-A does not differentiate the [outlet valve] main door from the auxiliary door and internal valve doors. This picture only shows the handle; the On/Off switch and auxiliary flap (which appears to be pointing at whole door). Also instructions are a little confusing. So I made the mistake of partially opening the main flap instead of the auxiliary flap. Then I proceeded to finish the rest of the maintenance MEL procedure. I asked Mechanic Y to take a look at the MEL procedure and told him what I had done. He agreed that the MEL was confusing and agreed with what I had done. Then Mechanic Y did an Avionics Equipment Ventilation Computer (AEVC) Test and finished paperwork. We heard on the radio that the airplane was coming back to the gate. Air turn back [due to] avionics outlet skin air valve main door was not fully closed; [causing] an avionics vent fault.Then Mechanic Y and I did more research involving Aircraft Maintenance Manual (AMM) 21-26-00 and Task 21-26-00-040-002 that made it very clear on position required of main/auxiliary [outlet valve] flaps and Deactivation Procedure. We re-accomplished Deactivation Procedure in accordance with MEL and AMM 21-26-00 and Task 21-26-00-040-002; re-accomplished the Avionics Equipment Ventilation Computer (AEVC) Test and paperwork. Suggest better labeling of figures/drawings and procedures in MEL 21-26-04 and more classroom/hands-on training.

Data retrieved from NASA's ASRS site as of July 2013 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.