Which of the following is not a typical ARPA alarm trigger?

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ARPA alarms are triggered by events that affect collision risk or the integrity of target tracking. When a new target appears inside a guard zone, the system treats that as a potential risk and raises an alarm to prompt attention and action. If a tracked target is lost, an alarm is generated because the operator can no longer rely on accurate tracking and must reacquire or reassess the situation. An ARPA failure also prompts an alarm because the automatic tracking capability is compromised and the operator may need to switch to manual monitoring or repair the system. On the other hand, AIS data improving visibility does not itself trigger an alarm; it simply enhances the information available to the operator and ARPA may use it to augment display, but it does not constitute a warning event.