Date: 201202
Local time of day: 0001-0600
Location: ZZZ.Airport, US
Light: Night
Aircraft: MD-88
Operator: Air Carrier
Operating under: Part 121
Mission: Passenger
Flight phase: Takeoff / Launch
ATC / advisory: Tower ZZZ
Aircraft component: Hydraulic System Lines; Connectors; Fittings
Reporter organization: Air Carrier
Reporter function: Inspector; Technician
Reporter qualification: Maintenance Powerplant; Maintenance Airframe
Human factors: Training / Qualification; Situational Awareness; Distraction; Confusion; Communication Breakdown; Time Pressure
Second reporter function: Technician
Anomaly: Aircraft Equipment Problem Critical; Deviation / Discrepancy - Procedural Published Material / Policy
Detector: Person Flight Crew
When detected: In-flight
Result: Flight Crew Returned To Departure Airport; General Maintenance Action
Contributing factors: Procedure; Aircraft; Chart Or Publication; Equipment / Tooling; Human Factors; Manuals
Primary problem: Aircraft

Narrative: The MD-88 aircraft that I worked the night before had an air turn back. I was assigned the task of removing a borrowed flap actuator and replacing it with another Air Carrier's Flap Actuator. I did not bleed the [Hydraulic] System the way it was stated in the Aircraft Maintenance Manual (AMM) because I was unable to view the whole content of the hyperlink at that time. I bled the pressure down without putting the Bypass Lever in the bypass position in the [Main] Gear wheel well. But I made sure there was not anyone onboard the aircraft or any power on the aircraft as well as using the 'Out of Service' Tag. I also did not pin the Main Gears out. I was pressed for time and had not done that specific job on this aircraft before but had a pretty good idea and the AMM reference to go by without the hyperlink for that one specific step where it states to put the Bypass Lever in the bypass position and pin the Landing Gears.

Callback: Reporter stated the air turnback was due to a Main Landing Gear (MLG) door 'Unsafe' light appearing in the cockpit because the MLG Gear doors would not fully close and lock after MLG retraction. That MD-88 aircraft had a previous history of hydraulic issues. There are two Hydraulic Bypass handles: one handles outboard and forward of the right wheel well to unload hydraulic pressure on the MLG doors and the other in the left wheel well; for the Spoiler Bypass Valve which unloads System Hydraulic pressure. Initially; there was some confusion because he was told a Maintenance Manager had gone out to the returned MD-88 and found the Spoiler Bypass handle in the 'open' position in the left wheel well. That was the bypass handle he was referring to in his report. He had not touched that Spoiler Bypass handle on the MD-88 during the overnight Service Check he and Mechanic Y had worked.Reporter stated he was later told; the right bypass handle was found not fully stowed; but than; no one could explain why the MLG gear door latches were locked on the ground. Further trouble shooting later determined that a Hydraulic Check Valve was by-passing hydraulic pressure and thought to be back-feeding through the electric Auxiliary Hydraulic Pump (AUX); which was 'Off'; sending hydraulic pressure to the 'Return' hydraulic line in flight; not allowing adequate hydraulic pressure to fully close the MLG doors. On the ground however; the electric Hydraulic AUX pump would be running; supplying hydraulic pressure to the system. After that was determined; he was told the event was not his fault.

Second narrative: The day the incident took place; myself [as Technician Y] and Technician X were assigned on an MD-88 aircraft which included a Work Package of a Service Check; and a Hydraulic Actuator Removal/Replacement (R/R) due to the fact it was a borrowed part from another Air Carrier. Mechanic X was the Aviation Maintenance Technician (AMT) in charge. I was instructed by him to start working on the Service Check portion of the Work Package and that he would get started on the flap actuator change. I did not touch the Hydraulic System; due to safety; since Technician X was going to be involved in the flap actuator change. Since those were the direct instructions I was given; I went out to the gate and started my walk around and continued with the rest of the Service Check; in which I encountered a couple of issues which I addressed. One was the left engine CSD oil level 'low'. I went back into the office and I saw Technician X there. I told him I had an Engine #1 CSD oil level low; and that I was going to be taking care of that. I tried looking for the equipment to perform the Task but other AMTs were using it. By the time I was done servicing the CSD; I went back inside and I saw Technician X with paperwork for the part that he was going to remove; so me and him walked out to the aircraft and he asked me to help him remove the cover for the [flap] actuator; which I did and once it was off; he asked me to look for caps to cap the two hydraulic lines going to the actuator. I went inside the Maintenance Office looking for caps; the caps were not where they were suppose to be; so I asked the Lead AMT to help me look for it [the caps] and we found them after about 30-minutes. When I went back to the aircraft with the caps; the part was already out and Technician X was no where to be seen; so I went back to the office and I saw Technician X with the part on the [Bench] vise swapping [hydraulic] fittings. We waited for the Inspector to arrive and once he did we went to the airplane to install the part. I was helping Technician X install the part in front of the Inspector. Once the part was installed; he asked me to install the cover and he left. I installed the cover and once everything was done I started doing paperwork. By this time; hours had passed and I did not touch the Hydraulic System. I was [so] distracted by the task at hand that I completely forgot that I had not touched [accomplished] the Hydraulic Inspection portion of the Service Check. When I was doing the paperwork I did sign for it but I did not remember that I had left it untouched [not accomplished] due to the fact Technician X was going to be working on a component that involved hydraulics. I left it [hydraulics] untouched for the safety of Technician X. I was never aware of the steps Technician X had taken to remove/install the flap actuator. I was just helping him with whatever he asked me. I was not shown the Aircraft Maintenance Manual (AMM) or anything so I wouldn't know if he did; or did not; follow the AMM procedures. I believe what led to this air turnback was miscommunication between the two of us and the complacency of doing the same job over and over again and letting it go by without noticing; even though I signed for it. But even after the work was done; I did not notice the bypass handle sticking out; not after the part was changed and nor before; when I was performing my walk around.


Synopsis: Two Line Maintenance Technicians report on their involvement with an MD-88 aircraft's Main Landing Gear (MLG) doors hydraulic bypass handle that was initially believed responsible for an air turnback.