Separation Minimums (Air Traffic Control)
Overview
Separation minimums in air traffic control are prescribed vertical and horizontal distances maintained between aircraft to ensure safe operations within controlled airspace. These standards are established by national aviation authorities, based on ICAO Doc 4444, and ensure aircraft are separated from each other, the ground, and protected airspace.
Vertical Separation
Vertical separation is maintained by assigning aircraft different altitudes or flight levels, using a standardized altimeter pressure setting. According to ICAO, the minimum vertical separation for IFR flight is:
- 1000 ft (300 m) below FL290
- 2000 ft (600 m) above FL290
- When RVSM (Reduced Vertical Separation Minima) is applied, 1000 ft is used up to FL410.
Lateral Separation
Lateral separation ensures aircraft remain horizontally apart by:
- Position reports over different geographic locations
- Assigned tracks that diverge by specific angles depending on the navigation aid used, with at least one aircraft 15 NM from the facility
Longitudinal Separation
This ensures sufficient spacing between aircraft flying the same or diverging tracks. Methods include:
- Comparing position report times
- Speed control to prevent overtaking
- Reduced separation if the lead aircraft is faster
Surveillance-Based Separation
When radar, ADS-B, or MLAT systems are in use, separation minima vary:
- 5 NM standard (ICAO minimum)
- 3 NM if surveillance capabilities permit
- 2.5 NM between aircraft on final approach within 10 NM of runway threshold, with additional criteria
Wake Vortex Turbulence
Additional separation is required to prevent hazards from wake turbulence. Aircraft are categorized by MTOM, and greater spacing is required for lighter aircraft following heavier ones. The exact spacing depends on runway configuration and flight phase.
Emergency Separation
If standard separation cannot be maintained in an emergency, vertical separation may be temporarily halved:
- 1000 ft becomes 500 ft
- 2000 ft becomes 1000 ft
Flight crews must be advised if emergency separation is applied.
References
- ICAO Doc 4444 – Procedures for Air Traffic Management
- ICAO Annex 2 – Rules of the Air
- ICAO Annex 11 – Air Traffic Services
- SKYbrary: Separation Standards
