Which of the following is NOT a terminal interrupt in a Link 16 system?

In a Link 16 system, a terminal interrupt is an event that requires immediate action from the terminal or affects its operational capability. The correct answer is built-in test (BIT), which is a self-diagnostic tool integrated within the system to check its functionality and status but does not necessarily indicate a failure or immediate need for operational response.

BIT is designed to be a background function that checks system integrity without interrupting normal operations. In contrast, network synchronization, data transmission errors, and power loss are conditions that directly impact the terminal's ability to communicate effectively and require immediate attention or corrective action. Network synchronization ensures all units on the network operate in unison, while data transmission errors indicate a failure in communication that can disrupt operations. Power loss, obviously, would terminate all operations until restored.

Therefore, BIT stands out as an essential but non-urgent process in this context, making it the option that does not fit the category of terminal interrupts.