Kerbal Space Program

The MainThrottle Axis Group is not selectable inside the action group screen only by editing the savefile obtainable.

Edit:

If you want to youse it, open the .craft file find your part, in AXISGROUPS set axisGroup to MainThrottle and delate MainThrottle from axisIncremental.

Example for the RoboticController

AXISGROUPS {
sequencePosition {
axisGroup = MainThrottle
axisIncremental = Pitch, Yaw, Roll, TranslateX, TranslateY, TranslateZ, WheelSteer, WheelThrottle, Custom01, Custom02, Custom03, Custom04
axisInverted = None
overrideIncremental0 = Pitch, Yaw, Roll, TranslateX, TranslateY, TranslateZ, MainThrottle, WheelSteer, WheelThrottle, Custom01, Custom02, Custom03, Custom04
overrideIncremental1 = Pitch, Yaw, Roll, TranslateX, TranslateY, TranslateZ, MainThrottle, WheelSteer, WheelThrottle, Custom01, Custom02, Custom03, Custom04
overrideIncremental2 = Pitch, Yaw, Roll, TranslateX, TranslateY, TranslateZ, MainThrottle, WheelSteer, WheelThrottle, Custom01, Custom02, Custom03, Custom04
overrideIncremental3 = Pitch, Yaw, Roll, TranslateX, TranslateY, TranslateZ, MainThrottle, WheelSteer, WheelThrottle, Custom01, Custom02, Custom03, Custom04
}
}