A Mechanic reports a B737-300 had returned to gate after pushback due to an inoperative Flap System. The Flap Bypass valve Cannon plug was found disconnected. The # 3 Flap Transmission had been replaced and a Flap System Rig and adjustment procedure accomplished earlier.
Synopsis
A Mechanic reports a B737-300 had returned to gate after pushback due to an inoperative Flap System. The Flap Bypass valve Cannon plug was found disconnected. The # 3 Flap Transmission had been replaced and a Flap System Rig and adjustment procedure accomplished earlier.
Narrative
Upon coming to work I was informed by a fact finding letter that the aircraft I worked on; had Returned to Gate after Pushback due to inoperative Flap System. It was discovered that the Flap Bypass valve Cannon plug was found disconnected. Aircraft was scheduled for Hangar Routine Overnight (RON) to Remove and Replace (R&R) the #3 Flap Transmission. Myself and co-worker were assigned this Task. Upon entry to the Hangar; found the hydraulic and flaps system were deactivated. One of the proceeding steps requires the flap Bypass valve Cannon plug to be disconnected and lock-out plate installation on valve. We R&R the #3 Flap Transmission and then proceeded to rig the flap system. Prior to putting power (hydraulic) on the flap system we re-activated the system. I removed the flap Bypass valve Lock-out plate and reconnected the Cannon plug. I know it was connected and secure. We then proceeded to Rig the Flap System; which requires the Flap/Slats to go full 'up' to full 'down' travel many times; which we did. Both Left and Right Wing Flap System required rigging. After rigging out the Flap System; we proceeded to safety the flap Torque Tubes retaining screws that were removed (earlier) to facilitate other Maintenance (F.O.M.); that being the disconnecting of the flap Torque Tubes for rigging adjustments. The retaining screws are reinstalled after the Torque Tube is reconnected. Panel installation and clean-up also started as other co-workers came to help. The Flap System was not operated again as the Rig and Operational Check was complete. I was on top of the Left wing working the #3 Flap Transmission area to finish and clean-up. I was not aware of who was doing what on the lower side of the aircraft.After I finished what I was doing on top of the wing I came down and saw that all else was completed also. Quality Assurance (QA) had also been there the whole time for RII and 'O.K. to Close' on panels. I then signed off the paperwork as required. Briefly stated: I connected the Cannon plug; the flaps worked fine; and I did not disconnect the Cannon plug at a later time.
NASA callback
Reporter stated further investigation revealed that one of the Mechanics who was reinstalling the Flap Torque Tube retaining screws was having difficulty getting access to the hole in some of the screw heads in order to run the safety wire through and secure the screws. So the Mechanic had disconnected the Flap Bypass valve Cannon Plug to lock out the Flap Hydraulic Drive Motor and allow him to manually rotate the Torque Tube to get access to those screws.Reporter stated the other Mechanic noted his intentions were to leave the Cannon plug disconnected only momentarily. But he did not attach any red streamers or flags to the disconnected Cannon plug; or make a write-up. All the RII Inspections had been accomplished including the Operational Checks. After completing the safety wiring of the screws; the Mechanic had completely forgotten about the disconnected Cannon plug. Reporter stated he was the one who had signed-off all the paperwork.
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Source: NASA Aviation Safety Reporting System (public domain). Reports are voluntary submissions and are not verified by NASA.