What must be done if a pilot deviates from their filed flight plan?

When a pilot deviates from their filed flight plan, notifying air traffic control immediately is crucial for several reasons. Air traffic control (ATC) is responsible for maintaining safe separation between aircraft and managing airspace effectively. When a pilot makes a deviation—whether due to weather changes, emergencies, or other operational factors—prompt communication with ATC allows them to update their information and manage air traffic accordingly.

Timely notification helps ensure that ATC can provide any necessary assistance, coordinate with other aircraft, and adjust flight routing to maintain safety. This communication is also important for legal and operational compliance, as deviation from a filed flight plan could have implications in terms of regulations and airline procedures.

In contrast, considering a minor deviation as insignificant and choosing to do nothing could lead to safety risks or a breakdown in communication. File a new flight plan retrospectively is not a correct approach, as the proper procedure requires immediate notification of changes rather than attempting to alter historical records. Waiting until arrival to report the deviation could result in dangerous situations and does not ensure immediate corrective action can be taken if necessary. Therefore, notifying air traffic control is the responsible and required action when a pilot deviates from their filed flight plan.