What must departing aircraft that will be vectored immediately after takeoff be assigned?

Departing aircraft that will be vectored immediately after takeoff must be assigned initial headings before departure. This ensures that pilots are aware of their intended course right from the start of their flight, allowing them to prepare for any immediate maneuvers they need to make once airborne. By providing initial headings in advance, air traffic control facilitates a smooth transition from ground to air operations, ensuring safety and efficiency in the departure process.

Providing headings before departure also helps in creating a standardized protocol that aids in separation and sequencing of aircraft, particularly when immediate vectors are necessary due to traffic congestion or changing operational needs. It allows the pilot to follow the planned departure route without delay, thus improving overall air traffic flow.

Other options suggest assigning headings at various points in relation to the runway or altitude. However, these do not align with the procedure aimed at ensuring clarity and readiness for the aircraft as it takes off. Assigning headings after takeoff or based on altitude would not provide the same proactive communication required for immediate vectoring.