Date: 201208
Local time of day: 0601-1200
Location: ZZZ.Airport, US
Light: Night
Aircraft: Dash 8-100
Operator: Air Carrier
Operating under: Part 121
Mission: Passenger
Flight phase: Parked
Aircraft component: Hydraulic System Lines; Connectors; Fittings
Component problem: Improperly Operated
Reporter organization: Air Carrier
Reporter function: Technician
Reporter qualification: Maintenance Airframe; Maintenance Powerplant
Human factors: Confusion; Situational Awareness
Anomaly: Aircraft Equipment Problem Critical; Deviation / Discrepancy - Procedural Published Material / Policy
Detector: Person Maintenance
When detected: Routine Inspection
Result: General Maintenance Action
Contributing factors: Human Factors; Manuals
Primary problem: Human Factors

Narrative: A Dash 8-100 had a temporary flexible [hydraulic] line that the Lead had told me to change. The line was difficult to change and also was in a bad spot to access. It was in the top inboard corner of the nacelle up against the rear spar. I had to loosen 5 additional [hydraulic] lines to get access to the specific line that I was changing. The fitting attached to that line was loose; and therefore made it more difficult to tighten the line. I had to open a panel on the top of the nacelle to get a wrench on the fitting so I could hold that line to tighten it. I did a leak check and a found that the line had leaked; so I had to loosen all of the lines to get to the leaking line again to tighten it sufficiently. After the second leak check the line was found to no longer be leaking. I then proceeded to confirm that all the other lines were tightened. [A few days later] the Maintenance Supervisor approached me and informed me that other mechanics were trying to clear an MEL related to the line that I had changed a few days before. The other mechanics that were working to resolve the MEL found that there was no hydraulic pressure going to a line [because] I had mistakenly switched it with another line. It was discovered upon further investigation that 2 of the lines; which I had to remove to get to the temporary flexible [hydraulic] line; had been swapped with each other. The incident occurred because there were many lines preventing clear access to the line that I was changing. The task required me to loosen various other lines to gain access to the temporary flexible [hydraulic] line. Two lines that I need to remove to facilitate access were small; looked very similar; and were side by side; so I must have interchanged them without noticing when I reconnected them. The fair-leads that were removed to access the line were reinstalled using retained hardware so it seemed as if I had installed the previously removed lines correctly. A satisfactory operational check was accomplished; further leading me to believe that the lines had been installed correctly. In the future I will be sure to mark the lines in a clear manner as to allow them to be reinstalled without any confusion as to where they need to be reconnected. Asking a fellow mechanic to go behind me and double-check my work can also help prevent future mishaps regarding attention to detail.




Synopsis: A Maintenance Technician inadvertently swapped two hydraulics lines on a Dash 8-100 while replacing a temporary flexible hydraulic located in the pylon/nacelle area. It went undetected during his leak check and manifested itself in service. The resultant condition was subsequently covered by an MEL; and discovered during the follow up maintenance troubleshooting. The lines were returned to their normal positions and the aircraft was returned to service.