How to Make a SimplePlanes Mod
This video will show you how you how to make a simple mod for SimplePlanes. You will need version 5.3 of Unity (no other version will work) and the SimplePlanes Mod Tools package.
Links:
Unity 5.3.6f1 for Windows 64-bit - https://ouo.io/V3oCgjw
Unity 5.3.6f1 for Windows 32-bit - https://ouo.io/U7aY4n
Unity 5.3.6f1 for macOS - https://ouo.io/h1lVhe
Standard Assets for Unity - https://ouo.io/DuHss4
SimplePlanes Mod Tools - https://ouo.io/BvXNBX
Win, Mac and Linux Platform Support - Click on "Download Module" in the "File - Build Settings" panel
Note: you can have as many versions of Unity as you'd like installed side-by-side on one computer.