When should a pilot inform ATC about a deviation from an ATC clearance due to a TCAS II RA?

When a pilot encounters a Traffic Collision Avoidance System (TCAS) II Resolution Advisory (RA), it is crucial to inform Air Traffic Control (ATC) as soon as practicable. This means that while the pilot must adhere to the immediate actions required to resolve the RA, they should communicate the situation to ATC as soon as they are able to do so safely. Prompt notification allows ATC to be aware of the situation and manage air traffic more effectively, ensuring safety for all aircraft involved.

The term "as soon as practicable" indicates that the pilot should prioritize safe maneuvering while also understanding the importance of keeping ATC informed to facilitate a proper response to the deviation. This balancing act of safety and communication is vital in maintaining situational awareness for both the pilots and ATC.

In contrast, informing ATC immediately upon detection may not always be feasible, as the pilot must first execute the necessary actions to ensure the aircraft's safety. Waiting until just before the next waypoint may delay ATC's situational awareness and could increase the risk of encountering another aircraft. Reporting only after landing would not provide ATC with the critical information needed to direct other aircraft and manage airspace effectively.