1.1 Preparing for texturing

I assume, that you already have your 3D model ( imported from FSDS ) in Gmax.
If not, and you don't know how to do it, read this tutorial by Fraser Turner:
FSDS Gmax Tutorial

I also assume, that you have prepared BMP textures like this:

Textures like this ( stretched to border, with different aspect ratio ) are used by many designers, in order to simplify textures mapping in FSDS ( or older AF99 )
We could use them in Gmax too.
Also remember, that texturing in Gmax is a bit different than in FSDS. Maybe it's more complicated, but it's more powerful.
We are actually applying not only texture but a material, which may include a map ( texture )

So let's do some texturing.
Open your imported model from FSDS and follow the next step.

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1.2 Texture assigning

Click "Material navigator" icon and and then select Browse from > File system
Find your BMP texture ( you can doubleclik on it to view it ) and "drag and drop" it from Material navigator onto desired part in some viewport:

This is the quick way to create simple material with texture and apply it on part at the same time.
You probably don't see yor texture yet, only the part with changed color. This is because your part doesn't know, how to apply the new texture.
You can close ( or minimize ) the Material navigator and follow the next step.

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1.3 Texture mapping - entire object

Select the part, you just assigned with the texture.

Select "Modify" tab on Command panel and then select "UVW Map" from "Modifier list"

Now you finally see your texture on your part, but it is not positioned right.
Don't vorry, We could modify it by editing UVW Mapping parameters.

If you look at "Parameters" rollout, you can see, that there is "Planar" mapping checked.
It seems appropriate for our fuselage, so leave it as is ( you can try to select another methods, and you'll see what will happen )
Look a bit below for "Alignment" ( you can drag the rollout using your mouse, if you don't see it ) and try to select one of check boxes x, y, z.
For our fuselage example "X" is suitable
Then select "Fit" button below. Now you can see your texture stretched to part's borders.

You probably see, that your texture is rotated about 90 degrees.
We will fix it by modifying the UVW mapping "Gizmo"

Click "+" at UVW Mapping line in Modifier Stack and select sub-object called "Gizmo".

Now you can move, rotate or scale it, without affecting the part position, it will affect only texture.
So select "Rotate" tool and rotate the gizmo.

You can rotate it by hand, by clicking on desired axis and rotating it by mouse dragging.
If you want to do it precisely, I recommend to set the "Angle snap"

( click on its button to activate it and right-click on it, to set its parameters - e.g. 15 degrees )

You can also rotate desired object by typing exact value in "Transform Type-In" box on status bar, or in the special panel, which you can display by right-clicking on move, rotate or scale tool button.
So in our case we type 90 in "X" box.

Then click "Fit" again, to stretch the texture to part's borders.

Now we would like to see only the bottom half of our texture, so change the "V Tile" to 0.5,
and now it's OK.
We also need to "Flip" direction in "U Tile"

Now you have your part correctly textured.

But when you look at the right side of your fuselage, you will see the same texture, which is also mirrored. If your part is textured on both sides with the same mirrored texture, you can stop here and start to texture another part.
But If you have e.g. different logo or readable text on each side, we need to do something more.
So follow the next step.

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1.4 Texture mapping - sub-object selection

We would like to map our texture on the right side using different way. We can do it by selecting desired polygons and apply the UVW Mapping on them, just like in step No.3.
But in order to keep our previous mapping, we should do our selection "after" our previous mapping.
We can do it by applying modifier "Mesh select".

So apply it and then select "Polygon" sub-object and select appropriate polygons.

If you want to see your active part only, select it and then select "Hide unselected" in "Display"tab:

Then you can select desired polygons in front view like this:

Or you can select them in "Right" view. Hit "R" shortcut or right-click on text ( upper left corner ) in some viewport and select View > Right
Then check checkbox "Ignore backfaces" :

and select whole part with crossing window:

Now only right half of part's polygons is selected :

Then select "UVW Map" from Modifier list again and do similar steps like we did on left side:
Mapping ... Planar
Alignment ... X
Alignment ... Fit ( it helps us to see texture's rotation )
UVW Mapping > sub-object Gizmo > Rotate 90 degrees
Alignment ... Fit
V Tile ... 0.5
U,V Tile Flip, if necessary

Now it seems, that our part looks just like before these steps, but there is one difference - we can adjust this new mapping on the right side independently to left side.
Select "Gizmo" sub-object in last UVW Mapping and move its position in viewport down using "Move" tool - you can click on blue arrow "Z" and drag it down.

This isn't maybe precise engough in our case ( texture stretched to borders ), so we would like to move it with some accurate value.
We have this value already, it's our texture "Lenght" in Mapping parameters.
So instead of moving the gizmo by mouse dragging, type this value in "Type-in" box under "Z". Because we want to move it down , type -4.004 and hit "Enter"

Now you have your part correctly textured.