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On a recent commercial flight (A320neo), I noticed some materials attached to the leading edge of a slat (no photo available). The attached material was not smooth, it rather looked like a small ball of steel wool. Making pilots aware of it, I was told this was a temporary repair for a dent.

I was satisfied for the moment, but rethinking the matter later, I wondered if dents can be temporarily fixed by spoiling the airflow, I would rather have expected a smooth foil or plate to restore the nominal flow. The aircraft continued its next legs without noticable delay.

How are dents in wings temporarily fixed?

Can pilots judge, if a damaged fix is within allowable limits?

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  • $\begingroup$ I would imagine it's the ground-based mechanics, more than the pilots who determine what's necessary to get the plane in the air. Of course, it's the pilot who has the final say (legally and it's his life on the line, not the mechanic's), but again, I'd imagine they lean heavily on their mechanics. Much the same way you and I do when we take our car in for major service or minor repairs. $\endgroup$ – FreeMan May 31 '19 at 14:28
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What usually happens is the crew doing the walkaround spots something that looks like damage, calls airline maintenance, and techs come look at it. For a ding, they will consult the Structural Repair Manual guidance on allowable limits on dents. Based on the SRM it may be ok to leave as is, or require repair, or require further evaluation.

If the SRM doesn't cover it, or not all the eventualities, they will call the OEM's product support organization for an assessment, repair scheme, and a temporary "fly-by" (a fix deadline) if feasible. A really big airline may have its own internal structural engineering team with its own design approval authority up to some level of severity, in which case it's all done in-house. Smaller airlines will call the OEM and pay the OEM for its engineering services.

In any case if it's outside the SRM limits, somebody somewhere with authority has to review the dent and decide what to do.

We don't really know what was done in the case you saw, so I'll speculate that the "ball of steel wool" you saw was actually the dent but looking like a bump due to lighting, and the area was probably roughened with Scotchbrite or something similar during the inspection, creating a steel wool look. There could have been a Non-destructive Test done (usually dye penetrant) to look for cracks in the surface where the metal was bent, which would make the surface look different from the surrounding area with the treatment process. Also if there were sharp defects like a gouge, there was probably some "blending" of the local material to minimize the stress riser effect of the gouge and the blending with emery cloth (sandpaper) would certainly leave a steel wool look to the area.

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