Final answer:
If the aircraft cannot be contacted after a certain period of time, the responsibility of initiating the EXCOM falls on the authority in charge.
Step-by-step explanation:
If the aircraft cannot be contacted after a certain period of time, the responsibility of initiating the EXCOM falls on the authority in charge, such as the air traffic control or the airline company. In case of an aircraft going missing or failing to establish communication, these authorities have protocols in place to follow to ensure the safety and well-being of the passengers and crew.