Narrative:

I was assigned to work on aircraft X at ZZZ (hangar) with my co-worker. We were performing eco. Coworker printed out the eco [engineering change order] work card; we gathered required equipment; went to the aircraft and performed elac software update. The second portion of the eco was to disconnect 2 wires from the back of the rack of each elac. We read the procedure from eco together; accomplished the task; performed tests; upgraded the cards and after every test passed closed it all up and went to production to sign the work card. We realized that the second portion of the work card (wiring disconnecting) is not printed out for us to sign. We asked for it to be printed. Promptly signed it and went home. Next day my coworker performed identical work card again and found on the last page of the eco that effectivity for his aircraft is not applicable for wiring removal from the elac's. He re-checked the effectivity for aircraft X we worked on the day before and realized that the wire removal procedure (second part of the eco) was not applicable for aircraft X either. He promptly informed [maintenance control] and aircraft X was taken out of service. The event occurred because the effectivity page was found towards the end on the last page of the eco after all the work steps were already performed and we both missed it. Usually effectivity is applied before printing work cards and it is found in the beginning of the work steps. The work-card has many pages and none of us ever performed such procedure before. Raining conditions and being short on time didn't benefit us either.I suggest to move the effectivity page towards the front of this eco. We will make sure to double or triple check every step of the work card in the future even if it takes much longer. Safety is my priority and there is no room for unsafe events like this to be repeated.

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Original NASA ASRS Text

Title: Technicians reported misreading an ECO; resulting in non compliance with established procedures.

Narrative: I was assigned to work on Aircraft X at ZZZ (hangar) with my co-worker. We were performing ECO. Coworker printed out the ECO [Engineering Change Order] work card; we gathered required equipment; went to the aircraft and performed ELAC software update. The second portion of the ECO was to disconnect 2 wires from the back of the rack of each ELAC. We read the procedure from ECO together; accomplished the task; performed tests; upgraded the cards and after every test passed closed it all up and went to production to sign the work card. We realized that the second portion of the work card (wiring disconnecting) is not printed out for us to sign. We asked for it to be printed. Promptly signed it and went home. Next day my coworker performed identical work card again and found on the last page of the ECO that effectivity for his aircraft is not applicable for wiring removal from the ELAC's. He re-checked the effectivity for Aircraft X we worked on the day before and realized that the wire removal procedure (second part of the ECO) was not applicable for Aircraft X either. He promptly informed [Maintenance Control] and Aircraft X was taken out of service. The event occurred because the effectivity page was found towards the end on the last page of the ECO after all the work steps were already performed and we both missed it. Usually effectivity is applied before printing work cards and it is found in the beginning of the work steps. The work-card has many pages and none of us ever performed such procedure before. Raining conditions and being short on time didn't benefit us either.I suggest to move the effectivity page towards the front of this ECO. We will make sure to double or triple check every step of the work card in the future even if it takes much longer. Safety is my priority and there is no room for unsafe events like this to be repeated.

Data retrieved from NASA's ASRS site 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.