How air traffic control approach radar works

A plain-English guide to the approach (APP) controller's job — and how you do it in the simulator.

Approach control is the radar unit that handles aircraft in the busy airspace around an airport — the terminal area (TMA/CTA). It sits between the en-route area control centre (ACC), which works high-level traffic between airports, and the aerodrome tower, which owns the runway. The approach controller's job is to take a stream of arrivals descending from the airways, turn them into a tidy, safely-spaced line for the runway, and to climb departures away from the field and hand them up to the ACC.

The radar picture

You work on a PPI (plan-position indicator) — a top-down radar scope with the radar site at the centre and a sweep rotating around it. Every aircraft appears as a target with a data block showing its callsign, altitude, speed and destination, and a short history trail of where it has been. Range rings and a compass scale help you judge distance and bearing at a glance.

Separation and STCA

The controller's first duty is separation: keeping aircraft apart. In a terminal area the standard minimum is 3 nautical miles horizontally or 1,000 feet vertically (5 NM en-route). If two aircraft are predicted to lose separation, the Short-Term Conflict Alert (STCA) warns you visually and aurally so you can act in time.

Radar vectoring

The main tool is vectoring — assigning headings to steer aircraft. You turn arrivals onto a downwind leg, then a base leg, then onto the extended runway centreline for the approach, spacing each one behind the last. Departures are usually turned onto their SID track and climbed out of the way.

Levels, QNH and the transition level

You climb and descend aircraft by clearing them to a level. Below the transition level aircraft fly altitudes set on the local pressure (QNH) in feet; at or above it they fly standard pressure flight levels (e.g. "flight level one zero zero"). Every instruction is read back and numbers are spoken digit-by-digit to avoid mistakes.

Speed control

Assigning speeds fine-tunes the spacing in the arrival stream without constant turns — slowing a leading aircraft or an aircraft that is catching the one ahead, so the whole sequence arrives evenly spaced at the runway.

The ILS approach

Most arrivals finish on an ILS (Instrument Landing System). The localizer gives lateral guidance along the runway centreline and the glideslope gives the descent path (typically 3°) to the touchdown zone. You vector the aircraft to intercept the localizer, clear it for the approach, and it captures the localizer and then the glideslope down to the runway. Where there is no ILS, aircraft fly an RNP/RNAV approach to a similar final path.

SIDs, STARs and holding

STARs (Standard Terminal Arrival Routes) funnel arrivals from the airway boundary toward the approach; SIDs (Standard Instrument Departures) take departures from the runway out to the airways. When traffic backs up, you can send an aircraft into a holding pattern — a racetrack over a fix — until there is room in the sequence.

Handoffs and phraseology

When a flight leaves your airspace you hand it off: arrivals to the tower, departures and overflights to the next sector. Everything is done in standard R/T phraseology so it is unambiguous over a noisy radio.

Try it yourself

The ATC Radar Simulator models all of this — real airports, radar vectoring, ILS approaches, SIDs and STARs, holdings, separation/STCA and live R/T audio — free in your browser. Pick an airport and take the approach controller's seat.