How to turn off cellular radio in Lollipop/JellyBean using adb?
From DavisNT answer on Stack Overflow,

There exist a simple workaround on rooted devices.
To enable Airplane Mode the following root shell commands can be used:
settings put global airplane_mode_on 1
am broadcast -a android.intent.action.AIRPLANE_MODE --ez state true

To disable Airplane Mode these root shell commands can be used:
settings put global airplane_mode_on 0
am broadcast -a android.intent.action.AIRPLANE_MODE --ez state false