Final answer:
If an aircraft loses communication with ATC, it will follow Lost Communication Procedures which include continuing the flight plan, squawking a specific transponder code, and adhering to specific flight instructions based on the phase of flight.
Step-by-step explanation:
If an aircraft loses communication (lost comm) with Air Traffic Control (ATC), the first thing it will do is follow a predetermined flight plan called the 'Lost Communication Procedures' or 'Lost Communications Procedures' (LCP). These procedures are designed to ensure the safety and separation of aircraft in the absence of communication.
During lost comm, the aircraft will continue its flight based on its last assigned altitude and route, and will adhere to specific instructions depending on its current phase of flight (such as initial climb, en route, or approach).
Additionally, the aircraft may squawk a specific transponder code (such as 7600) to alert ATC and other aircraft of the communication loss.