On manual
Definition 1 of 2
Pro Tip 1/3Human Involvement
Emphasize the need for a person to take action, unlike automatic processes. 
The crane is malfunctioning, we need to operate it on manual.
Pro Tip 2/3Unexpected Situations
Often used when technology fails or isn't trusted, requiring manual oversight. 
After the power outage, the security gates are remaining on manual.
Pro Tip 3/3Control Transfer
Indicates a deliberate switch from automatic to hand-operated control. 
Due to the storm, the pilot switched the plane's navigation to on manual.