Hey Kev. It sounds like your light map is making your texures invisible. Is this only happenning when you turn the lights on at night? And are you compiling with has lightmap checked?
Also if when your building the aircraft if you are not using the edit clone from the drop down on the top and then using the mirror modifier from the drop down parametric deformers this will cause the parts to go transparent or textures to be inside out. In my experience you'll have to retexture any parts that you mirror. Grouping and cloning may some times cause the parts to be transparent also.
To fix the lightmap problem you must make an all black texture 256-256 and name it texturename_L or _LM. Then in your material manager click on your _Ts and unlock the ambient and diffuse color. Click on the little square next to ambient choose bitmap then choose the _L or _LM that you made that will link it to your textures and should take care of the trasparencies. Do this for all your textures that are affected.
If this does'nt work there is always a recent post here that has some more info. Try going back a few to find one.
There is yet another way to get around This problem. You could model all your lights and assign gmax materials to them with the name conventions given in the SDK and export without lighmap checked.
Also I have'nt tried this yet but it may work. If your model has lighted windows or tail illumination you could after and without the light map checked just create an texture _L _LM and link it as above and export.
Some of these ideas should help you with your Gmax modeling.
What is the reason you are forced to use Gmax?

Glad to hear you got it fixed. I did'nt think about the has reflect map. I forget because I use model commander and have the Reflect map as a Parameter in the Parameter file.