A320
Maintenance Airframe; Maintenance Avionics; Maintenance Powerplant
Communication Breakdown; Time Pressure
Aircraft Equipment Problem Less Severe; Deviation / Discrepancy - Procedural MEL / CDL; Deviation / Discrepancy - Procedural Maintenance; Deviation / Discrepancy - Procedural Published Material / Policy
General Flight Cancelled / Delayed; General Maintenance Action
Aircraft; Human Factors; Procedure
I am the Avionics Lead Mechanic on midnight shift. One of the aircraft I watched over was aircraft. During the night it came in with an MEL for Number 1 left hand boost pump inoperative. Mechanics X and Y were assigned to the job. Avionics Mechanic Z was assigned to assist in troubleshooting with them. During the middle of the shift it was determined the fuel low pressure switch was faulty and replaced per MM (Maintenance Manual) 28-XX-XX. CB's were pulled and collared per MM. It was brought to Mechanic Z attention that ADIRU #3 and AOA sensor were faulty during a routine preflight check. Mechanic Z replaced both; but no help and MELed both out. I worked the day shift that morning and got a call saying that all 3 hydraulic quantity indications showed xx's; a no dispatch item. I found CB 131XP-A still collared with a streamer on it behind the observer seat. I reset it and indications came back to normal. Further investigation on my part found that the wrong CB had been collared during the low pressure switch replacement. This CB deactivated Number 3 ADIRU; Number 3AOA sensor; all 3 hydraulic quantity indications and both SDAC's; obviously a no dispatch situation. The CB that should have been pulled and collared was on correct panel; but 2 rows above. Pulling and collaring the wrong CB for Maintenance is very dangerous obviously.
Lead Technician reported discovering the wrong circuit breaker was pulled and collared during troubleshooting and repair of an unrelated problem caused three other systems to be degraded and improperly MELed.