Narrative:

I repaired a left system hydraulic quantity problem on aircraft X; a B767-300. The left hydraulic quantity was reading zero (0) when the reservoir was full. I found the problem. The quantity monitor was bad. I changed the monitor and confirmed this was a positive fix. I reviewed the maintenance manual (MM) and there was no special requirement for changing this part; so I followed the MM when I changed this part and cleared this item.twelve hours later; when I returned to work; I was assigned a different airplane with the same problem. I then noticed in MEL chapter 29-33-02 that when putting the hydraulic quantity system on MEL you have to disconnect the power transfer unit (ptu) signal wire. I then realized that I had not reconnected the ptu signal wire on aircraft X the day before.the cause of this problem is when you repair this system the MM for changing the quantity monitor does not mention anything about a ptu signal wire disconnection. This is only mentioned in the MEL; so when a mechanic is working this system when it is on MEL; they are not mindful of this ptu signal wire disconnection. The quantity will function normally with this wire disconnected.to prevent a recurrence of this; I think a separate MEL needs to be raised for this ptu wire being disconnected. That way a separate sign-off would be required to make sure this action is completed before the next flight.

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Original NASA ASRS Text

Title: An Avionics Technician reported the B767-300 Maintenance Manual (MM) does not call for the reconnection of the Power Transfer Unit (PTU) signal wire when replacing or reinstalling the left hydraulic system quantity monitor. He noted that MEL chapter 29-33-02 does call for the signal wire to be disconnected when deferring the quantity monitor.

Narrative: I repaired a left system hydraulic quantity problem on aircraft X; a B767-300. The left hydraulic quantity was reading zero (0) when the reservoir was full. I found the problem. The quantity monitor was bad. I changed the monitor and confirmed this was a positive fix. I reviewed the Maintenance Manual (MM) and there was no special requirement for changing this part; so I followed the MM when I changed this part and cleared this item.Twelve hours later; when I returned to work; I was assigned a different airplane with the same problem. I then noticed in MEL chapter 29-33-02 that when putting the hydraulic quantity system on MEL you have to disconnect the Power Transfer Unit (PTU) signal wire. I then realized that I had not reconnected the PTU signal wire on Aircraft X the day before.The cause of this problem is when you repair this system the MM for changing the quantity monitor does not mention anything about a PTU signal wire disconnection. This is only mentioned in the MEL; so when a mechanic is working this system when it is on MEL; they are not mindful of this PTU signal wire disconnection. The quantity will function normally with this wire disconnected.To prevent a recurrence of this; I think a separate MEL needs to be raised for this PTU wire being disconnected. That way a separate sign-off would be required to make sure this action is completed before the next flight.

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.