Figure 4-1.—The shipboard Link-4A CDS system.
After the aircraft receives the transmitted data, it
may respond by transmitting data to the controlling
station. This is the reception cycle. The receiver
removes the carrier frequency and forms the serial
data pulse train. The pulse train is sent to the data
terminal set via the switchboard. The data terminal
set converts the serial pulse trains into parallel data
and sends the data to the CDS computer.
In a typical aircraft carrier system, the four distinct
modes of operation in the Link-4A system are
intercept vectoring, air traffic control, automatic
carrier landing system, and precision course direction.
Intercept Vectoring
Intercept vectoring enables the controlling ship to
guide an aircraft to an intercept point. The two types
of data sent to the aircraft during intercept vectoring
are command data and situation data. Command data
provides direct steering and control information,
whereas situation data provides the aircraft with an
overall picture of the tactical situation with respect to
its target.
This data is used to guide the aircraft within
striking range of its target at optimum position and
altitude for an attack. The messages also contain
instructions to the pilot, such as target identity, break
engagement, and return to base.
Air Traffic Control
In the air traffic control mode, Link-4A is used to
control the aircraft in the carrier’s traffic pattern. The
control station transmits data to the aircraft to
maintain safe flight patterns and assigns priority for
landing approach. As each aircraft enters the landing
pattern, it is transferred to the automatic carrier
landing system for final approach and landing.
Automatic Carrier Landing System
The automatic carrier landing system selects
aircraft in the order of priority from the pattern and
enters them into the final approach. During the final
approach, a precision radar tracks the aircraft. Correct
information pertaining to the approach is transmitted
to the aircraft’s autopilot. When conditions are
unfavorable for a landing, the wave-off control is
initiated and the aircraft is guided through a short
pattern and the landing approach is repeated.
Precision Course Direction
The precision course direction mode is used in the
remote guidance of bomber and reconnaissance
aircraft, and drones. The guidance messages contain
pitch, bank, heading, altitude, and airspeed commands
to permit very precise control of the aircraft’s flight
path.
4-2
