Air Traffic Control
How Controllers Separate Airplanes.

RADAR

Separation by use of Radar

Separation of aircraft as expressed in the previous page is known as Procedural Separation. However a more efficient and expeditious method of separating aircraft is by means of Radar. Many countries in modernizing their air traffic control systems have moved to separation of aircraft by use of radar.

Radar is short for Radio Detection and Ranging and as used in air traffic services, is an electronic method of determining the location and direction of aircraft from the airport or radar station, once those aircraft are within the serviceable range of the equipment.

If you remember, longitudinal separation is the method applied to provide a required spacing between airplanes flying at the same level or altitude and along the same route. Radar separation is the most expeditious method of separation in any of two dimensions, laterally and longitudinally.

Using radar, the controller can now literally "see" the location and determine the actual distance of aircraft from the airport. He can also determine the distance between the airplanes themselves and can make use of the information to separate airplanes longitudinally or laterally (side by side). The separation applied is usually a minimum of 3 or 5 nautical miles between airplanes depending upon circumstances.

As aircraft approach to land in an active radar environment, the radar controller will instruct aircraft to adjust their airspeed and their direction of flight in a manner which will safely position aircraft 3 to 5 miles apart longitudinally, and place them on an imaginary extended straight line about 8 to 10 miles from the runway. From this position there will then be continuous movement of airplanes towards the runway, with each aircraft separated from the one in front by the required 3 or 5NMs. Departing aircraft must also be separated laterally from arriving aircraft by the required 5 NM, if not possible at the time, then must be separated vertically by 1000 feet until they cross each other and are at least 5 NM apart.

Piarco airport is equipped with radar. Controllers can control most aircraft within approximately 200 miles of Mt. Catherine where the radar equipment is located.

In the light of modern electronic radar equipment, you may wonder then if procedural control is not an obsolete system. The problem is that there are still many areas of the world where it would be impossible, or not practicable to install radar equipment - like over the high seas. In some cases, where it may be practicable, it is not cost-beneficial.

While Piarco uses radar for separation, only approximately 10 % of the airspace under its control, 
(that area within the semi--circle in this diagram), can be covered by its radar. Consequently, procedural separation has to be applied within the remaining 90% of the airspace.

END