Pressing the split axis pushbutton after the AP is engaged allows the pilot to manually control which axis?

When the split axis pushbutton is pressed after the autopilot (AP) is engaged, it enables the pilot to manually control the roll axis while the autopilot maintains control of the pitch axis. This feature allows the pilot to selectively take command of the aircraft’s roll maneuvering without disengaging the autopilot entirely.

The design of this function supports operational flexibility by allowing the pilot to make specific adjustments to the aircraft's performance while still maintaining the stability and altitude control provided by the autopilot in the pitch axis. This ensures that the crew can respond to changing flight conditions or enhance the maneuverability of the aircraft as needed while benefiting from the autopilot's stabilizing functions on the other axis. Hence, the ability to control the roll axis directly is a critical aspect of the split axis feature in the C-17.