Here's another way to do it.
Go into each default aircraft's folder that you want to remove as AI traffic. For example lets delete the Ford Tri-Motor as AI. So go into the
FS9/Aircraft/Ford_Trimotor folder. In that folder open up the
aircraft.cfg file using MS Notepad (if you have it). You should see something like this:
[fltsim.1]
title=World Travel Airlines Tri-Motor
sim=Ford_Trimotor
model=
panel=
sound=
texture=1
kb_checklists=Ford_Trimotor_check
kb_reference=Ford_Trimotor_ref
atc_id=NC8407
ui_manufacturer=Ford
ui_type="Tri-Motor"
ui_variation="World Travel Airlines"
description=
Under the line that says:
title=World Travel Airlines Tri-Motor
Using notepad or another simple text editor simply edit the .cfg file by changing the name
World Travel Ailrines Tri-Motor
to something else.
So for this example lets change the name to
World Travel
Lines
Tri-Motor
By doing that when FS9 goes into the default
.bgl traffic file to use that particular variant as AI traffic, it will look for the same name that is in the .bgl file to fill in that aircraft in that line of the AI traffic file. It won't be able to find that aircraft in your FS9/Aircraft folder since we re-named it to something else. The aircraft is still there, you can still fly it in the sim, but it simply has a different name.
Best of all it won't show up as AI traffic since the aircraft's name has to exactly match the name listed in the .bgl file.
Give that a try and see if that works for you.
Just remember that some aircraft like the Tri-Motor and 737, 747 have multiple paint schemes, each that have their own line of code in the aircraft's .cfg file. To eliminate each paint version as AI traffic you have to change the name of that individual paint variant to somehting else in the .cfg file.