Gulfstream IV / G350 / G450
Maintenance Inspection Authority
Other / Unknown
Aircraft Equipment Problem Less Severe; Deviation / Discrepancy - Procedural Maintenance
General Maintenance Action
Human Factors; Procedure
Subject aircraft recently had a 72-month inspection completed. During the inspection a technician noted in the work order that all 8 flap tracks had several areas of various levels of corrosion. The tracks were subsequently worked against the appropriate drawings and with support from [company] engineering and tech support. Ultimately it was determined that the tracks were beyond limits in tested areas and would need to be replaced. Both left and right wing rear beams were completely disassembled to facilitate replacement of all 8 tracks. This disassembly included all hydraulic lines and flight control cables.The 72-month inspection was completed and all 8 flap tracks were replaced with new parts. The wing rear beams were reassembled and a post-maintenance flight check was performed with minor findings reported by the flight crew and onboard maintenance support. There was no report of any hydraulic problems or fluctuations during this flight. In fact; it was not until the 3rd owner flight that the problem was discovered and reported to maintenance upon returning to home base.Evaluation of the aircraft revealed that during reassembly of the left and right wing rear beams; the right side was reassembled with two hydraulic lines crossed. One flight and one combined system line was crossed. The error was discovered by using the identification markings on the lines and tracing them from the inboard section of the wing outboard. The lines were corrected and all operational checks were satisfactory.The in-work; inspection; okay to close and final inspection processes are being reviewed.
A Inspector Authority Mechanic reported that a Gulfstream IV; after extensive maintenance; had two hydraulic lines in the right hand wing crossed and were not discovered until after a couple flights.