Example of VISCOM
The white light indicates that an aircraft has entered the ATC system and
is receiving RADAR service, is on a downwind or base leg, or is 15 miles
out on a straight-in approach.
The amber light indicates that the aircraft has reached a point 6 miles
from touchdown or the end of the runway, and clearance is requested to
The green light indicates that the aircraft is approaching 3 miles from
touchdown or end of runway, and clearance is requested for landing,
touch-and-go, or low approach, as applicable. The tower controller clears
the aircraft by activating the green light switch, causing the light to
become steady in both facilities.
The red light indicates that the aircraft is to discontinue its approach to
the runway. The tower controller activates the red light by depressing the
button, causing the light to flash in both facilities, and furnishes the
reason for denying or canceling the clearance.
Table 5-2 -- Examples of VISCOM
CONTROL TOWER EQUIPMENT
At any location where terminal air traffic control (ATC) operations are conducted, the
control tower is the hub of the ATC complex. From this hub, all clearances for landings
and takeoffs originate even though the aircraft may be under the direct control of a
RADAR approach control or ground controlled approach (GCA) facility. The tower local
controller provides final clearance for runway usage. As new methods and equipment
are installed at duty stations, every air traffic controller should study diligently--not only
the method of operation but also the capabilities and limitations of the equipment and
The Airfield Lighting Control System (AFLCS) (AN/FSN-7) allows control towers to have
remote control of airfield lighting circuits. The airfield lighting can be energized either
from the tower cab or a remote site (lighting vault).