Three mechanics and one Inspector report about the removal and reinstallation of a #5 Leading Edge Slat and proximity sensor Targets on the slat Auxiliary tracks of a B767-300ER. The inboard and outboard Targets had been swapped; causing an in flight Stick Shaker activation and an air turnback. The Maintenance Manual and Functional Tests were found inadequate.
Synopsis
Three mechanics and one Inspector report about the removal and reinstallation of a #5 Leading Edge Slat and proximity sensor Targets on the slat Auxiliary tracks of a B767-300ER. The inboard and outboard Targets had been swapped; causing an in flight Stick Shaker activation and an air turnback. The Maintenance Manual and Functional Tests were found inadequate.
Narrative
Myself and another Aircraft Maintenance Technician were issued a Task Card XXXX to remove the #5 Slat off of a B767-300; for [fixed wing] leading edge repairs under the slat. We followed the procedures outlined in the Task Card for the preparation and removal of #5 Slat. We also marked the hardware and put them in parts bags and hung them on the structure where they were removed; for reinstallation when the repairs were completed.We were given the task to perform the Functional Test of the #5 Slat on Task Card XXXX; Item 6. We checked that the paperwork was complete to that point; and we proceeded to perform the required tests of the Slat System per the Task Card instructions. It passed these tests and we sold (verified) this to Inspection.We were told of the air turn back more than two weeks later and advised to fill out this NASA form detailing what we accomplished with this particular Task Card. We were also told what the problem with the air turn back [was] and subsequent repairs to remedy this issue.
Second reporter narrative
Was given Task Card with another Mechanic; to remove #5 Slat. Removed #5 Slat; reference Routine Task Card. Placed removed hardware in bags at location it was removed from. Placed slat on wing stand. At a later date; myself and Mechanic Y were issued [re-installation] Task Card to complete. Installation Step #5 had already been completed and signed by the installing Mechanic and stamped by Inspection. We proceeded to Testing; Step 6; with fellow Mechanic Y in flight station and me on ground in communication using Service Interphone. Fellow Mechanic Y in flight station ran Test; Step 6; while I kept flight control surface clear from ground. Slat operated normally from ground view. Now as to what happened next is just what I've been told; I didn't personally witness the events. The plane evidently flew 3-4 days with Stick Shaker issues and on one flight the pilot decided to turn back to the departure airport. Upon investigation; the Slat Targets were found to be installed incorrectly. As to what caused them to be installed incorrectly; I can't say I wasn't there. These Targets can be installed in the opposing position and the slat manually operated without damage.Maybe lack of attention to detail; or lack of familiarity with the aircraft system. Lack of training was probably an issue because my understanding is that the Mechanic in Bay-6 assigned to install the slat was assigned a mechanic's helper and another mechanic from Bay-1 who doesn't work 767's. I know the Task Card does not include clear indication as to which Target goes where. I think photographs of Inboard (I/B) and (O/B) Targets stating their position and included in the Task Card might help to prevent a recurrence.
NASA callback
Reporter stated the #5 Slat is located at the outboard side of #1 engine. Their pre-pulled Job Cards that cover component installations and their Maintenance Manual (MM) did not identify the specific locations for the Inboard and Outboard Targets; which were later found in opposite positions on the slat Auxiliary Tracks.Reporter stated that on rotation out of ZZZ; and while transitioning from 'Gear-Up' with flaps retracting; the Asymmetry light flashed for two seconds in the B767-300ER flight deck. But there were no 'A' level messages displayed on the cockpit EICAS screens. He believes the flight crew experienced another Stick Shaker; similar to previous reports; so crew returned to field. Aircraft was ferried to Reporter's Maintenance Base where trouble shooting found the Auxiliary Track Targets installed in opposite locations.Reporter stated the Targets are suppose to be matched at three positions to indicate the leading edge slats are at 'Full Up'; 'Full Out' or 'Mid-position'. The Functional Test they had performed; when the slat had been reinstalled; was later found to be 'not adequate' for identifying or at least not differentiating when the Targets were mis-positioned. Reporter stated their maintenance procedures now include interrogating the Proximity Sensor Electronics Unit (PSEU) black box to a deeper level; and not just at the Leading Edge Proximity Sensor Test level; but deeper; by dialing in specific sub-systems; anything that has sensors; to test for 'Near' or 'Far'; Sensor to Target Resistance/ Inductance values which will show if there is incorrect Target installations and includes checking the Flaps/Slats Electronics Units (FSEU) for faults. Reporter stated when they were initially trouble shooting the cause of the Stick Shaker; after the B767-300 had been ferried back to Base; Maintenance could not duplicate the Stick Shaker condition; even though the PSEU identified the Targets as a problem. One of the mechanic's mentioned the leading edge needed some type of air load applied to the slat; which is what he did by pushing on the #5 Slat and immediately the cockpit Stick Shaker activated. The reason the flight crew only saw the Asymmetry light flash momentarily just above the Gear handle and no EICAS messages and no immediate Asymmetry Lockout occurred in flight was due to the slat Targets were still meeting near the Sensors on the wing structures. But during retraction; with just the right amount of air load at certain slat positions; the Stick Shaker would activate.Reporter stated their Engineering group has requested Boeing update their Illustrated Parts Catalog (IPC) Manual to specifically identify the proper locations for the Inboard two inch Targets and the Outboard four inch Targets.
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Source: NASA Aviation Safety Reporting System (public domain). Reports are voluntary submissions and are not verified by NASA.