Communication - Lesson Three
- ATC Positions, Control Areas and Functions -
ATC Positions
When you fly Online
you'll communicate with several ATC stations, like Shannon Control
(EISN_CTR), Dublin Approach (EIDW_APP), Dublin Tower (EGAA_TWR), Cork
Ground (EICK_GND), etc. Each control station name consist of a
geographical name (Shannon, Dublin, Cork, etc.) and a position name
(Center, Approach, Tower, etc.) that reflect the station's - geographical and functional - area
of responsibility. So, by knowing the name of an ATC station you'll
know the airspace it controls and the duties it performs. In this
article we'll describe the area of responsibility and typical functions of each ATC position. The ATC positions in
hierarchical order are:
CTR = Center Controller - responsible for controlling traffic outside the TMA*
APP = Approach Controller - responsible for arriving traffic inside the TMA*
DEP = Departure Controller - responsible for departing traffic inside the TMA*
TWR = Tower Controller - responsible for traffic within sight of the active runway and traffic on the runways
GND = Ground Controller - responsible for aircraft movements on the ground - except traffic on the runways
DEL = Clearance Delivery - responsible for issuing IFR clearances to aircraft on the ground, before departure
FSS - Flight Service Station - responsible for providing weather data to and communicating with VFR traffic
* TMA = terminal movement area (airspace around a busy airport), see below for details
Control Areas
Air Traffic Control is a
worldwide network of ATC stations. Each ATC station is responsible for
the traffic within a certain segment of airspace. When you cross an
airspace boundary you must terminate contact with the controller of the
airspace you are leaving and establish contact with the controller of
the airspace you are entering. This process is called a "HANDOFF".
Airspace is segmented horizontally and vertically. Horizontally,
airspace is divided into contiguous segments called Flight Information
Regions (FIR's). A FIR is usually divided into smaller Control Areas
(CTA's). FIR's adjoin like the peaces of a puzzle. Within each FIR,
however, around busy airports, there are packets of airspace that require special attention. Such packets of airspace known
as "Terminal Movement Areas" (TMA's) fall under the supervision of
another group of controllers, specialized in controlling airport
traffic. Therefore control areas around airports are concentrically overlapping, like
coins laying on each other, creating a vertical segmentation. Higher
ranking controllers control the higher and bigger layers (coins closer
to the top of the heap) that contain
several lower ones. For example, a FIR may contain several TMA's with
several Approach Controllers and a TMA may contain several airports
with several Tower Controllers.
ATC Functions
In league with the vertical segmentation described above, different ATC positions have different functions:
- DEL - Clearance Delivery: The
main task of Delivery is to verify and - if needed - modify
flight plans and give permission for IFR flights. In the real world
aviation there is a separate person dedicated to this task. In our
virtual reality, the Delivery position is rarely manned. If you fly
Online and there's no Delivery, you should always request clearance
from the lowest ranking controller Online. Clearance for IFR flight includes:
- Destination airport
- Flight plan modifications (if there is any)
- Departure instructions (SID, initial climb)
- Transponder (Squawk) Code
- GND - Ground Controller: Ground control is responsible for safe aircraft movements
on the ground, except on the runways, and for the effective use of the
airport's gates and taxiways. Ground gives clearance to taxi from the
gate to the runway or back, approves startup and shutdown, etc.
- TWR - Tower Controller: The
main duty of Tower is, generally, to manage aircraft movements on the
runways and give takeoff/landing clearance to departing/arriving
aircraft when the runway is free or instruct them to hold
short/go-around when it is not. Tower controls aircraft in the
immediate vicinity of the airport (usually within 10 nm and below 5000
ft). Tower usually hands over departing aircraft to Departure or
Approach at an altitude of 2000 ft and takes over arriving aircraft
when they are established on the Glide Slope.
- DEP - Departure Controller: Departure
and Approach are responsible for the separation and fluent flow of
traffic around the airport. At most large airports (except in the USA)
departing aircraft usually fly Standard Instrument Departure (SID)
routes and so require little attention. Therefore, a separate Departure
controller is usually available only at peak times. During the more
quiet hours, Approach handles departing aircraft as well. Departure
usually hands over aircraft to the Center controller at the border of
the TMA or when it's reached its first waypoint, usually an airway
intersection.
- APP - Approach Controller: Approach
guides aircraft down from the last waypoint of their flight plan, or
the boundary of the TMA to the airport and lines them up with the
runway for the final approach. Arriving aircraft are usually given
vectors and speed instructions during approach to ensure separation and
a fluent flow of traffic, even when a STAR (Standard Terminal Arrival
Route) is used. In case of congestion, Approach will ask you to enter a
holding pattern or make left/right orbits (360 degree turns). Once
lined up with the runway, Approach will clear you for the approach and
hand you over to the Tower.
- CTR - Center Controller: The
main duty of the Center controller is to provide radar service
(separation) to all en route traffic. Center monitors all flights
within its airspace, enforces compliance with the flight plans, gives
clearance for altitude and route changes on pilots' request or when the
weather or traffic requires, and occasionally gives vectors or holding
instructions. In our world of virtual aviation Center often substitutes
other unmanned (Offline) stations within its control area provided his workload permits it.
|