Date: 201201
Local time of day: 0601-1200
Location: ZZZ.Airport, US
Light: Daylight
Aircraft: A320
Operator: Air Carrier
Operating under: Part 121
Mission: Passenger
Flight phase: Climb
Airspace: Class B ZZZ
ATC / advisory: Tower ZZZ
Aircraft component: Aircraft Cooling System
Component problem: Malfunctioning
Reporter organization: Air Carrier
Reporter function: Technician
Reporter qualification: Maintenance Powerplant; Maintenance Airframe
Human factors: Communication Breakdown; Training / Qualification; Workload; Time Pressure; Confusion; Situational Awareness
Second reporter function: Technician
Anomaly: Aircraft Equipment Problem Critical; Deviation / Discrepancy - Procedural MEL / CDL; Deviation / Discrepancy - Procedural Published Material / Policy
Detector: Person Flight Crew
When detected: In-flight
Result: Flight Crew Returned To Gate; Flight Crew Returned To Departure Airport; General Maintenance Action
Contributing factors: Logbook Entry; Procedure; Manuals; MEL; Human Factors; Chart Or Publication; Aircraft
Primary problem: MEL

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.


Second narrative: An A320 aircraft returned to gate after pushback due to avionics vent fault. I went to determine what was wrong with it and found avionics vent skin air outlet valve fault.  Contacted Maintenance Control and we agreed to defer the vent skin air outlet valve using MEL 21-26-04. Mechanic X came to help me. He accomplished the MEL maintenance procedure and I did the Avionics Equipment Ventilation Computer (AEVC) Test and signed the paperwork.


Synopsis: 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.