For rudder trim, the ALTN position of the TRIM SEL switch does what?

In the context of the C-17’s rudder trim system, when the TRIM SEL switch is placed in the ALTN position, it utilizes a separate electrical source. This design feature ensures that if the primary electrical source is compromised or fails, the rudder trim can still operate effectively, maintaining the safety and controllability of the aircraft.

The ability to switch to an alternate source allows for redundancy in the system, ensuring that pilots can adjust the rudder trim as needed for optimal performance and control during flight, especially in scenarios where system reliability is crucial. This redundancy is a key aspect of modern aircraft design, providing a backup that enhances safety and operational capability.