Here are slightly better instructions, based on ID's comment :

DO NOT COPY THE QUOTATIONS "..." I USED DOWN BELOW WHEN NAMING FILES. THESE QUOTATIONS ARE JUST HERE FOR CLARITY'S SAKE.

Go to where the game is installed on whatever drive you use, usually "C:\Program Files (x86)\Steam\steamapps\common\Janes Advanced Strike Fighters\inputconfig\" and create a "Backup" folder there
Put all the ".xml" files in that "Backup" folder
Then copy the "XBOX 360 Controller.db.xml" file from the "Backup" folder back into the "inputconfig" folder
Rename that "XBOX 360 Controller.db.xml" into "default.db.xml"

Disable "Steam Overlay" by right clicking on the game in your Steam library and going to "Properties", and the "General" tab
Disable "Steam Input" by doing the same thing and going to the "Controller" tab

Start the game, select "Control Option"s, and then "Control Configuration". On that screen, press the "End" key for a few seconds until the controls change and are set properly.

This still does not fix the stuck left yaw issue

How to use the XBOX360 Controller (English Translation)

1. Disable data input from the gamepad because it is interfering with the data.
Disable STEAM OVERLAY during game. force STEAM input to be set to OFF for each game. Force BIG PICTURE controller option to be set to OFF.

2. Prepare to load the standard XBOX360 controller settings.
\Find the folder \SteamApps\common\Janes Advanced Strike Fighters\inputconfig\ and create a new folder with an appropriate name and throw in a file with the xml extension.
Copy XBOX 360 Controller.db.xml from the folder to \Janes Advanced Strike Fighters\inputconfig\ and rename it default.db.xml.

3. Start the game, select Control Options, and then ControlConfiguration. On that screen, press the End key for a few seconds to confirm initialization.