Final answer:
In the context of organizational responsibilities, the Air Traffic Manager is generally in charge of designating an FWS (Flight Watch Supervisor) on duty during operational hours.
Step-by-step explanation:
The question relates to the management structure within a facility and who in the organizational hierarchy is responsible for designating an FWS (Flight Watch Supervisor) on duty. Concerning the options provided, a: Facility Manager, b: Regional Manager, c: Air Traffic Manager, or d: National Operations Manager, the most likely answer is c: Air Traffic Manager, given that the Air Traffic Manager is typically in charge of the operations within a specific airspace sector or facility and would therefore be responsible for staffing decisions like the designation of an FWS.