What control is used with the backup position?

The backup position on the Dassault Falcon 7X uses the AMSAC control. This control is crucial for operating the aircraft's systems in a backup manner when primary controls are unavailable or have failed. AMSAC stands for Automatic Mach Speed Adjusting Control, which helps manage the aircraft’s speed during critical phases of flight, thereby maintaining safe operational parameters.

By utilizing the AMSAC control in the backup position, pilots ensure continued safe and effective management of flight operations, ensuring that the aircraft can still be controlled smoothly even in scenarios where primary systems may not be functioning as intended. This reflects the design and engineering focus on redundancy and safety within the Falcon 7X's systems.

The other options represent different control mechanisms that either work in a normal operational mode or relate to auxiliary power and controls but do not specifically pertain to the backup functionality.