Air Traffic Control functions

Moderator Location : UK Spotter Watch Member : No

Courtesy Ranger 703 and Darkstar.

London Mil(Swanwick) and Scottish Mil(Prestwick)are both Area Radar units looking after primarily military aircraft,but also civil aircraft off route,in the middle and upper airspace.The units are split into sectors with controllers looking after their own bit of airspace.AAR areas are also generally supported by these units.Both have Distress and Diversion cells for aircraft in emergency or lost amongst other things.This is just the tip of the iceberg but I will cover it more later,unless of course another soul contributes.

At military airfields,commonly known as Terminal units,the number of radar positions depends primarily on airfield size and number of aircraft operating.Again a quick brief on the main positions:

Ground:Controls aircraft on the manouevering area and deals with warnouts,pre-notes etc.

Local:Controls the runway and visual circuit.Clears aircaft to take-off and land.

Approach:Controls aircraft within approx 40miles of an airfield requiring a radar service either on departure or within the vicinity.This is a very brief description,as this position can fulfill many radar roles.

Director:Directs aircraft to the airfield until they are either visual or able to conduct a Precision approach or Instrument landing.May also conduct surveillance radar approaches.

Zone:Gernerally controls aircraft operating below a certain level within the vicinity of an airfield such as GA under a Flight Information Service,this position varies greatly from airfield to airfield.Lyneham zone for example is very busy throughout the year,whereas Lossie is not generally so.

PAR(Precision Approach Radar):Guides aircraft down an imaginary centreline and glidepath for the last 10 miles or so before touchdown.

ILS(Instrument Landing System):Same as above,but the aircraft and computers determine the approach.At military airfields a controller will monitor these approaches.

Moderator Location : UK Spotter Watch Member : No

And added to by TONKS.

To add to what has been said above, there are 5 types of service provided by ATC that you may here asked for/offered:

a. Radar Control. A mandatory service where the pilot cannot change height or heading without approval.

b. Radar Advisory Service (RAS). Controller offers advice to maintain required separation, also passing range, bearing and alt (if known) of conflicting traffic plus action required to avoid a confliction. There are lots of rules {censored} with this, but a pilot will often use RAS if he/she is IMC and the airspace is quite busy. The flight has to be being flown under IFR (Instrument Flight Rules) but can be asked for if in VMC (Visual Meteorological Conditions) or IMC (Instrument Meteorological Conditions). The pilot must advise that they are changing ht and heading and is responsible for their own terrain avoidance.

c. Radar Information Service (RIS). A lower and less restrictive service, where ATC will pass info on conflicting traffic, but will not give advice on avoiding action. Generally used by pilots who are VMC (ie can see the ac around them) or during quiet periods of IMC. Again, there are lots of extra rule {censored} with this, but the pilot is responsible for using the information he is being given and avoiding other ac.

d. Procedural Service. Non-radar ATC. The pilot will fly a procedure based on beacons/navigation kit. Separation is given on the reported heights and positions.

e. Flight Information Service (FIS). Another non-radar service and can be used in conjunction with other services. Controller are not responsible for separating or sequencing aircraft, but will pass information on weather , serviceability of navaids and the like.

Often you will here the term Limited Radar Service. This will be given with a stated reason, such as poor radar performance, near the overhead of the scanner etc.