Regional Jet 200 ER/LR (CRJ200)
Maintenance Powerplant; Maintenance Airframe
Distraction; Training / Qualification; Workload
Aircraft Equipment Problem Less Severe; Deviation / Discrepancy - Procedural Published Material / Policy; Deviation / Discrepancy - Procedural MEL / CDL; Deviation / Discrepancy - Procedural Maintenance
Flight Crew Returned To Gate; General Maintenance Action
Human Factors; Aircraft; MEL; Manuals; Procedure
I went out to a plane with another Mechanic (new to the company) to defer a left thrust reverser and show him how to do it. While deactivating it; I disconnected the cannon plug for the left cowl anti-ice valve by mistake. This mistake wasn't found until the next day when the plane was written up for a left cowl anti ice caution message on taxi out; and another Mechanic went to replace the valve. An FAA Inspector was shadowing him at the time. It looks like the plane did not fly in between the deferral and the write-up the next day.The Mechanic I was with was new and had never deferred a thrust reverser before; and I was concentrating on showing him the system and how to deactivate it; and making sure he had something useful to do other than watch me disconnect plugs and insert locking pins. I was concerned with disconnecting all the cannon plugs so that the plane wouldn't come back with a TR (Thrust Reverser) caution message; it didn't cross my mind that the cowl anti-ice valve was on the same harness and is one of the only two cannon plugs under the cowl that shouldn't be disconnected for the MEL. I'm not completely comfortable with training people; and that anxiety probably contributed to my mistake. We did have the manuals pulled up on a tablet with us; but I evidently did not pay close enough attention when I reviewed it.Have trainers work with the new mechanics. Maybe add a step in the MEL to actually ops check the cowl anti-ice to verify that it works; since it's apparently easy to disconnect it by mistake. The deactivation procedure in the AMM (Airplane Maintenance Manual) could be simplified also.
CRJ-200 aircraft Technician reported disconnecting the cannon plug of the anti-ice valve by mistake during deferral of thrust reverser.