Narrative:

I was assigned to work on an in-service A320 at the gate. The discrepancy was a noisy avionics ventilation fan. I was working with two other technicians; one of which was a special troubleshooter. We determined that the avionics ventilation extract fan was the source of the noise and needed to be changed. We were instructed by our lead to defer the fan instead. We called maintenance control to get authorization to apply MEL 21-26-02A. We then began to comply with the dispatch deviation guide (ddg). I verified the correct position of the air conditioning inlet valve 21 headquarters; and had another technician verify it as well. I began to complete the paper work while the other two technicians were complying with the items of the ddg in the cockpit. After completing the paper work I verified that the 'extract' push button was released and two circuit breakers where pulled and collard.after the aircraft left; we received word from the tower that the aircraft was returning to the field with a pressurization problem. We began to look at the information we had; to determine the cause of the problem. It was decided that the incorrect circuit breaker may have been pulled and collard. After the aircraft returned; myself and the other two technicians met it at the gate. I found that the wrong circuit breaker (D7); was pulled and collard. I removed the collar and reset the circuit breaker; then pulled and collard the correct circuit breaker (AE02). I then made sure that the rest of the ddg was completed properly and returned the aircraft to service.when verifying the work accomplished by the other two technicians; I believe that I allowed the presence of the troubleshooter; with his perceived experience and knowledge; influence my better judgment. My confidence in his abilities caused me to do a less thorough verification than I would normally have done. Consequently I did not catch the incorrect circuit breaker being pulled and collared. During the company investigation of the incident it was determined by the quality assurance investigator; that the MEL documentation is ambiguous; and (he) is currently working to get it changed.

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Original NASA ASRS Text

Title: A Mechanic working with two other technicians; is instructed by their Lead to defer; instead of changing; a noisy avionics equipment ventilation extract fan on an A320. The aircraft required an air turnback due to an incorrect circuit breaker was pulled and collared; preventing cabin pressurization.

Narrative: I was assigned to work on an in-service A320 at the gate. The discrepancy was a noisy avionics ventilation fan. I was working with two other technicians; one of which was a special troubleshooter. We determined that the avionics ventilation extract fan was the source of the noise and needed to be changed. We were instructed by our Lead to defer the fan instead. We called Maintenance Control to get authorization to apply MEL 21-26-02A. We then began to comply with the dispatch deviation guide (DDG). I verified the correct position of the air conditioning inlet valve 21 HQ; and had another Technician verify it as well. I began to complete the paper work while the other two Technicians were complying with the items of the DDG in the cockpit. After completing the paper work I verified that the 'EXTRACT' push button was released and two circuit breakers where pulled and collard.After the aircraft left; we received word from the Tower that the aircraft was returning to the field with a pressurization problem. We began to look at the information we had; to determine the cause of the problem. It was decided that the incorrect circuit breaker may have been pulled and collard. After the aircraft returned; myself and the other two technicians met it at the gate. I found that the wrong circuit breaker (D7); was pulled and collard. I removed the collar and reset the circuit breaker; then pulled and collard the correct circuit breaker (AE02). I then made sure that the rest of the DDG was completed properly and returned the aircraft to service.When verifying the work accomplished by the other two technicians; I believe that I allowed the presence of the troubleshooter; with his perceived experience and knowledge; influence my better judgment. My confidence in his abilities caused me to do a less thorough verification than I would normally have done. Consequently I did not catch the incorrect circuit breaker being pulled and collared. During the company investigation of the incident it was determined by the Quality Assurance Investigator; that the MEL documentation is ambiguous; and (he) is currently working to get it changed.

Data retrieved from NASA's ASRS site as of April 2012 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.