What actions should a crew perform to ensure unrestricted movement of flight controls post de-icing?

To ensure unrestricted movement of flight controls after de-icing, it is crucial for the crew to verify the full range of movement without interference. This step is essential because de-icing processes can introduce substances like de-icing fluid or ice remnants that may obstruct or hinder the operation of flight controls. By ensuring that all control surfaces can move freely and respond correctly, the crew helps maintain the aircraft's safety and performance.

The focus here is on the functionality of the flight controls, which directly impacts the aircraft's handling characteristics. Proper verification is a safety precaution that aims to prevent any potential control issues during flight, which could arise from leftover de-icing fluids or ice that might have refrozen on the moving parts.

The other choices, while important for overall flight safety and procedures, do not directly address the need for checking the flight controls' operation after de-icing. Communication systems, crew seating, and cabin security are all significant, but they relate to other aspects of flight readiness rather than the specific requirement to ensure that flight controls are unobstructed and operate effectively.