EMB ERJ 145 ER/LR
Maintenance Airframe; Maintenance Powerplant
Situational Awareness; Communication Breakdown; Confusion; Troubleshooting
Aircraft Equipment Problem Critical; Deviation / Discrepancy - Procedural MEL / CDL; Deviation / Discrepancy - Procedural Published Material / Policy
General Maintenance Action
Aircraft; Procedure; MEL; Human Factors
On the evening shift ending; June 2015; an EMB-145 aircraft was in ZZZ with a fuel system MEL (along with other items on the Bill of Work (BOW). The original squawk indicated that selecting the Fuel Transfer switch on the overhead panel to 'LOW' would supply fuel not only to engine selected; but also to that side's wing tank. Research indicated that this would happen selecting 'LOW' fuel in either direction.A thorough ops check for a lengthy period of time was performed; running APU and both engines trying to duplicate the squawk; trying all pumps and all combinations of switching. Completely unable to duplicate the squawk; I cleared the MEL.HOWEVER; in researching the squawk and MEL; I FAILED to completely review the Maintenance Procedures for MEL 28-XX-XX. As a result; I failed to properly completely 'de-MEL' the fuel system. It came to my attention early this morning that the Defuel Valve was found safety wire closed; obviously in that configuration from the original MEL. Failure to completely research and review all the MEL procedures. In addition to researching a squawk; COMPLETELY review ALL MEL procedures related to that squawk if same has been MEL-ed.
An Aircraft Maintenance Technician (AMT) was informed he had failed to completely review the Maintenance Procedures previously accomplished under MEL 28-XX-XX; when a Defueling Valve was found still safety wired closed after he had cleared the MEL. The deferral had noted when selecting the Fuel Transfer switch on the Overhead panel to 'LOW'; fuel would be supplied not only to the engine selected; but also to that side's wing tank.