This might be better put in the effects and shaders section, as no one has responded yet.
I don't know about the scenery object interface to effects when designing airport scenery (with WED?), yet. 3d objects like buildings should use the model shader by default?, and these should support normal maps?
Ground surfaces: If you are working on runways, there is a separate shader - this uses the regional definitions interface based on material names so you can override it with global improvements, or regional improvements, or even regional definitions for specific airports if you wanted to. Looking at data/Materials-base.xml it seems line features are defined there, using lfeat.eff which inherits from effects/runway.eff. Runway.eff supports a normal map. The related textures are in data/Texture/Runway. You can browse files & sub-folders within FGData online here:
https://sourceforge.net/p/flightgear/fg ... next/tree/It might help to say what exactly you are trying to do first.
Kind regards