Regional Jet 200 ER/LR (CRJ200)
Maintenance Powerplant; Maintenance Airframe
Distraction; Confusion; Communication Breakdown; Situational Awareness
Aircraft Equipment Problem Critical; Deviation / Discrepancy - Procedural Published Material / Policy; Inflight Event / Encounter Other / Unknown
Flight Crew Returned To Departure Airport; General Maintenance Action
Aircraft; Human Factors
A CRJ-200 aircraft was at ZZZ hangar for overnight work. Included was a generator problem that required an IDG change. This work was assigned to a Technician; and I [performed an] RII of the installation. The IDG removal went well and it was decided to take a look at the [Accessory Gearbox (AGB)] IDG BB Axis carbon seal for condition while it was off. The carbon seal was removed and noted to be degraded. Another seal and packing were ordered. Meanwhile; it was discovered; after the IDG unit was removed; that we had in fact removed the wrong IDG. (This was due in part to a handwritten note that was [left] with the Shift Turnover that stated Number 1 IDG when it should have been Number 2 IDG.) I was then notified that the seal was ready to be installed on the Number 1 Engine. I verified the correct torque; seating and positioning of the carbon seal installation; but did not witness the actual build up and seal placement. The left IDG was then re-installed; inspected for installation; and the right side [Number 2 IDG] removed. Both engines were leak checked at idle and visually inspected with no leakage noted. Yesterday; I was told the Aircraft X had an air turn back in ZZZ1 for oil loss on the Left engine. Apparently there was a problem with the carbon seal installation. At this time; I am not aware of additional details. After reviewing the AMM for carbon seal installation; it is apparent that the o-rings must be installed and seated properly for a leak free installation. At the time; I thought I had visually checked the seal installation adequately; but for leakage to occur with a new carbon seal there must have been issues with the o-rings; I should have been much more thorough in the inspection. Graveyard.
An Aircraft Maintenance Inspector was informed that a CRJ-200 aircraft had an air turn back due to loss of engine oil after takeoff. He had previously inspected a carbon seal replacement on the Accessory Gearbox (AGB) prior to re-installation of the Left Engine IDG.