When must the flight plan be updated after issuing a final altitude or routing?

The flight plan must be updated prior to track acquisition to ensure that the latest information is accurately captured and communicated to all relevant parties. This step is crucial because it aligns the flight plan with the current status of the flight, including any recent changes to altitude or routing that may have been issued to the aircraft. Updating the flight plan at this stage helps maintain situational awareness for both the flight crew and air traffic control, minimizing the risk of confusion or discrepancies between what is planned and what is actually occurring in-flight.

Additionally, updating the flight plan too late, such as after takeoff or upon arrival, would not provide the necessary real-time adjustments that are vital for operational efficiency and safety. Updating it before the aircraft reaches the departure point would also not capture any changes that might have occurred during the flight preparation phase. Therefore, updating the flight plan in advance of track acquisition is the most effective approach to ensuring that all operational data is current and accurate.