Air Traffic Skills Assessment (ATSA) Test 2025 – 400 Free Practice Questions to Pass the Exam

The standard longitudinal separation minima required between two IFR (Instrument Flight Rules) aircraft is typically 10 nautical miles (DME) or 20 minutes in time. This standard ensures that there is a safe distance and timeframe between aircraft to prevent any risk of collision, especially during ascent, descent, and en route flying.

Using 10 DME as a measure allows air traffic controllers to maintain effective separation when aircraft are flying on similar routes. The time-based separation of 20 minutes is particularly important in scenarios where the ground speed of the aircraft may vary, providing a more flexible and reliable means to ensure safe spacing in controlled airspace. This combination of distance and time helps to mitigate the risks associated with air traffic congestion and enhances overall flight safety.

The other options present varying amounts of distance and time, which do not align with the established standards for longitudinal separation in IFR operations.