What does it mean when an aircraft has an assigned beacon code but none is received?

When an aircraft has an assigned beacon code but none is received, it indicates that the aircraft has lost communication. This scenario typically suggests that while air traffic control has issued a specific squawk code for the aircraft to use, the transponder is not responding or transmitting the expected signal back to the radar. This can prevent air traffic controllers from receiving critical positional information about the aircraft, potentially impacting their ability to ensure safe separation and management of air traffic.

In contrast, the other possibilities do not accurately reflect the situation. For example, if an aircraft is in hold, it is still actively communicating and should still be squawking its assigned beacon code. A malfunction could technically lead to a lack of signal, but it is more accurate to state that the communication has been lost rather than definitively assigning a malfunction without additional information. When an aircraft is untracked, it means there may not have been an assigned code or proper identification, rather than specifically indicating a loss of communication with an existing beacon code. Thus, the loss of received signals while an assigned code is present primarily indicates a breakdown in communication.