Narrative:

[Maintenance technician] called in the pre-departure clearance (pre departure clearance) for aircraft X and that he had one defect in the logbook. Reported all lavs would not flush. There was water sprayed when the button was pushed but there was no vacuum. I told him it sounded like the vacuum blower was not working and to check 2 circuit breakers on the P91. The vacuum waste blower and the vacuum waste cont. He reported both breakers were set. I had him then check that the service doors were closed and they were. It was concluded to go ahead and put the blower on MEL because other than no vacuum; the lavs operated normally. Looking at the MEL; I instructed [the maintenance technician] to pull and collar the 2 breakers he had previously checked. This was part of the configuration change procedure in MEL 38-xx. While he was doing this; I emailed to his office the required placard to be placed on each of the lav doors. When [the maintenance technician] called back; we confirmed the 2 breakers that were pulled and I completed the logbook with him. We then completed the pre departure clearance and the aircraft was ready to depart ZZZ. [Later] dispatch was talking with aircraft X and that none of the lavs were operating and that he was going to return to ZZZ. Knowing that I had just worked that issue; I looked again at the MEL and discovered that I had instructed [the maintenance technician] to pull a breaker that was supposed to be closed. This breaker; vacuum waste cont; provides the power to each lav flush circuit and is required to be closed for the lavs to operate on the ground and in flight. This why the lavs were not operating. I spoke with the captain in flight and explained the situation and that his issue would be quickly resolved when back on the ground. After arriving back in ZZZ I spoke again with [the maintenance technician] and told him the situation and to remove the collar and reset the breaker. We did this and the lavs operated normally except for the vacuum function on the ground. An overweight landing inspection was completed as well as another pre departure clearance and the aircraft departed again with no further issues. It was a complete misread of the configuration change steps in the MEL. I would say the steps were hastily glanced over by myself instead of deliberately reading each word. What jumped out to me was the way in which the 2 breakers were identified: vacuum waste blower (F2) and vacuum waste cont (C11). In the MEL book; these names are directly inline horizontally and vertically with one another. The top one has you open the breaker but the one below has you verify that it is closed. Again; I just saw the 2 breaker names and knew I was making configuration changes by pulling breakers. MEL maintenance procedure step should be removed from the procedure where it currently is and placed as a prior 'note' or a 'caution' since the step is more of an advisory to make sure that the breaker is closed than it is a step with a required action; especially when the previous step has the action of opening it.

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Original NASA ASRS Text

Title: Maintenance personnel reported that the incorrect circuit breakers were pulled when deferring a Vacuum Waste Blower.

Narrative: [Maintenance Technician] called in the Pre-Departure Clearance (PDC) for Aircraft X and that he had one defect in the logbook. Reported all lavs would not flush. There was water sprayed when the button was pushed but there was no vacuum. I told him it sounded like the Vacuum Blower was not working and to check 2 circuit breakers on the P91. The Vacuum Waste Blower and the Vacuum Waste Cont. He reported both breakers were set. I had him then check that the service doors were closed and they were. It was concluded to go ahead and put the Blower on MEL because other than no vacuum; the lavs operated normally. Looking at the MEL; I instructed [the Maintenance Technician] to pull and collar the 2 breakers he had previously checked. This was part of the Configuration Change Procedure in MEL 38-XX. While he was doing this; I emailed to his office the required placard to be placed on each of the lav doors. When [the Maintenance Technician] called back; we confirmed the 2 breakers that were pulled and I completed the logbook with him. We then completed the PDC and the aircraft was ready to depart ZZZ. [Later] dispatch was talking with Aircraft X and that none of the lavs were operating and that he was going to return to ZZZ. Knowing that I had just worked that issue; I looked again at the MEL and discovered that I had instructed [the maintenance technician] to pull a breaker that was supposed to be closed. This breaker; Vacuum Waste Cont; provides the power to each lav flush circuit and is required to be closed for the lavs to operate on the ground and in flight. This why the lavs were not operating. I spoke with the captain in flight and explained the situation and that his issue would be quickly resolved when back on the ground. After arriving back in ZZZ I spoke again with [the maintenance technician] and told him the situation and to remove the collar and reset the breaker. We did this and the lavs operated normally except for the vacuum function on the ground. An Overweight Landing inspection was completed as well as another PDC and the aircraft departed again with no further issues. It was a complete misread of the Configuration Change steps in the MEL. I would say the steps were hastily glanced over by myself instead of deliberately reading each word. What jumped out to me was the way in which the 2 breakers were identified: VACUUM WASTE BLOWER (F2) and VACUUM WASTE CONT (C11). In the MEL book; these names are directly inline horizontally and vertically with one another. The top one has you open the breaker but the one below has you verify that it is closed. Again; I just saw the 2 breaker names and knew I was making configuration changes by pulling breakers. MEL Maintenance Procedure step should be removed from the procedure where it currently is and placed as a prior 'Note' or a 'Caution' since the step is more of an advisory to make sure that the breaker is closed than it is a step with a required action; especially when the previous step has the action of opening it.

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.