What should a pilot do after deviating due to a TCAS II resolution advisory?

Answer: C — Notify ATC of the deviation as soon as practicable.

The appropriate action for a pilot after deviating due to a TCAS II resolution advisory is to notify Air Traffic Control (ATC) of the deviation as soon as practicable. This is crucial because TCAS (Traffic Alert and Collision Avoidance System) advisories are issued to prevent collisions by providing pilots with instructions to alter their flight path. After executing the necessary maneuver to comply with the TCAS resolution advisory, informing ATC ensures that the safety of air traffic is maintained. By notifying ATC promptly, the pilot provides critical information that allows air traffic controllers to update other aircraft in the vicinity of the altered trajectory, facilitating better traffic management and reducing the likelihood of further conflict or confusion in airspace. This communication is essential for the safe and efficient operation of air traffic. In the context of the other options, returning to the last issued heading may not be safe or appropriate if it contradicts the TCAS advisory. Requesting ATC clearance for the deviation could unnecessarily delay the response to an immediate safety issue, and continuing on the last course does not acknowledge the urgency of the situation posed by the TCAS advisory. Thus, timely notification to ATC is the most effective course of action following a TCAS resolution advisory.