Towards the end of 2020, the maintenance team in Basel were performing a routine inspection as part of a D-Check, when they found some corrosion on the full Horizontal Stabilizer of the aircraft. Generally, when corrosion is found, the mechanics call the Sheet Metal team, who treat the affected area. However, this can remove varying amounts of the existing material, meaning that the team then needs to establish the remaining thickness to proceed with their work, and check if the aircraft remains airworthy, or if it needs structural repair.
This is achieved by the NDT (non-destructive-testing) team, who ascertain thickness through ultrasound techniques. When a surface has different thickness variations, the team 'maps' the area using a grid: square patterns of 2" by 2" (approx. 50x50mm), 1" by 1" (approx. 25x25mm) and 0.5" by 0.5" (approx. 13x13mm) are drawn directly on the affected surfaces. Larger squares are used where material loss is minimal, smaller squares are used to more precisely locate deeper points. In each square, the NDT inspector scans to find the smallest thickness value and writes it down in that square.
“Using this technique to this extent, on such a large and involved surface, is unique. It's a first for us at Jet, and a first on this aircraft type across the industry”
"It is not unusual to use NDT mapping in mechanical maintenance," says Alexandre Guyot, Program Director Large Aircraft. "But using it to this extent, on such a large and involved surface, is unique. It's a first for us at Jet, and a first on this aircraft type across the industry."
"This was on a massive scale that we have never seen before," says Frédéric Westpalm van Hoorn, Senior Manager NDT Shop. "We were in regular contact with the OEM, and had a dedicated team on the project: Gareth and Florian from Large Aircraft, who meticulously prepared the grid, specially designed tracing equipment made in-house by Jean-François from Sheet Metal, and Marc and Filippo from NDT, under the supervision of Baptiste, who spent countless hours to precisely assess the entire area and prepare a report for structural evaluation by OEM engineering services."
It was a huge, which required a lot of patience, attention to detail and teamwork. Thank you to everybody who was involved.
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