Have download the tool and did a small test on a fsx airport, but that's as far as I got. The PDF file says the user needs some knowledge, which I don't have. So would very much appreciate any help in using this tool and any other required to get the job done.
FSX2FS9 will remove from the FSX airport any FSX only elements. However this is probably not going to be enough - in most cases the result would need to be opened in an airport editor. It is actually quite a complex subject. Perhaps the best thing would be to try out a conversion, look at it in FS9 and see what you get.
It is going to be easier for us to help if you ask more specific questions.
So chances are you will need to edit the result in an airport editor. There are several available for FS9 such as AFCAD (which is now very old but still used by many folks), AFX which is payware and ADE which is free and is supported here on FS Developer.
So I tried it at a airport...KBKL. Opened fsx2fs9, put the airport Bgl in the input window. Made a test folder with that in the output and hit go. It did whatever it does saying it removed some taxi way sings and some other stuff.
Changed all the dds textures in the texture folder into .bmp textures. Made scenery/texture folders inside the main airport folder....added usual way in addon scenery, restarted etc etc.
But nothing showing. Maybe an area from above looking down where building might've been. No fs9 buildings showing either at aiport.
Did the converter again but not un-checking the buildings or objects boxes and generating a new Bgl file. No difference. Or changing texture format...dxt1/3 etc.
OK let's start with the question: Why are you converting a FSX airport back to FS9? AS you have discovered it is not an easy of straight forward task. Others may take a different view but I would say don't. If you are trying to enhance a stock FS9 airport then either use an airport editor to do it yourself or look for a third party addon that someone else has done.
What does show up: Well I can tell you what won't:
Generic buildings might show up but since FSX can used texture numbers that can't be used in FS9 they may look funny
Vehicle parking spots and vehicle paths
Fuel parking spots
Terminal buildings will probably not show at all since the stock FSX ones are special library objects
Also if the airport has any special textures or land class then they won't show up either.
Parking spot sizing for FS9 is different than for FSX so work may be needed on those also
So bottom line is unless this FSX airport is really really special then don't try to revert it to FS9. And it truth the things that make is special will probably not translate back anyway.
Well after all that negative stuff can you tell me what airport your are trying to revert?
Not really any airport as such. More perhaps some GA/bush strips which seem to look far better in fsx when it come to parking areas, taxiways etc with many in fs 9 just a strip of grass in between trees. I thought an easy solution was somehow figuring a way to improve the fs9 strips a little more.
Maybe I've got the wrong idea of what can be done.
Perhaps scenery design........is what I need to be looking at. Which could be a problem considering I dont know the difference between a mipmap and a bitmap.
I think you should look at using an airport editor to enhance existing FS9 tock airports. Certainly it is not worth reverting FSX ones. Also Airport editing tools will not need to to become involved in textures!.
There are three airport design tools that will work in FS9:
AFCAD. This is the 'granddaddy' of all editors and has been around a long time. Development stopped about the time FSX was released. It is free and will edit airports. It can't handle things like taxi signs or buildings
AFX is similar to AFCAD but supports both FS9 and FSX. It can handle taxi signs but not buildings and objects. It is payware
Airport Design Editor (ADE) will do what AFCAD/AFX do in terms of airport design. It can handle taxi signs, buildings, objects and so on. It is free.
I am not the right person to ask which of these is 'best' since I am the developer of ADE. However there is an active support forum here for ADE and folks who use all three of the tools mentioned above. I am sure they will be able to tell you which is best for which purpose