Dash 8-400
Maintenance Airframe; Maintenance Powerplant
Communication Breakdown; Training / Qualification; Situational Awareness; Distraction
Aircraft Equipment Problem Critical; Deviation / Discrepancy - Procedural Published Material / Policy
General Flight Cancelled / Delayed; General Maintenance Action
Human Factors
While in the process of an A-Check; I was assigned the duty of checking the filter units on the Pack Flow Control Valve and the Left and Right hand pack Bypass valves. After pulling the circuit breakers as directed in the Job Card; I proceeded to service the filters. Thinking the job would proceed smoother and I would be less likely to make a mistake; I decided to service both left and right hand units at the same time. After finishing; I returned to the flight deck to reset the circuit breakers and found that other technicians were on the flight deck doing other tasks. Not wanting to interrupt their work I decided to go to lunch and reset the breakers when I returned. After returning from lunch; I started a different task and forgot to reset the breakers. Upon arriving at work the following evening I learned that the line fitting on the Left hand Bypass valve hadn't been tightened enough; resulting in a cancelled flight. As a new Mechanic; I now realize that I should not have serviced both filters at the same but rather as separate tasks. I should have had another person inspect my work since it was my first time doing this task.  I should not have signed-off on the breakers being reset until after I had actually done it and I should have been more diligent about finishing the task after returning from break.  [Recommend] more emphasis on newer mechanics getting a task inspected; or a Job Card reviewed by someone else before assuming the job was done correctly; especially the first time they are performing the task no matter how simple it seems.
A Line Aircraft Maintenance Technician (AMT) was informed that a line fitting on the Left Pack Bypass valve had not been tightened enough and circuit breakers had not been reset on a DHC-8-400 aircraft; resulting in a cancelled flight. He had previously serviced the filter units on the Pack Flow Control valve and Left and Right Bypass valves.