The obvious difference between RADARs used on board ships and RADARs used
ashore is that shipboard RADARs are on a continuously moving airfield. For this reason,
most shipboard RADARs are gyroscopically and/or computer stabilized. These features
allow the presentation you see on the RADAR repeater to remain oriented (magnetic
north at the top of the scope) even though the ship is in a turn. There is also a ship
heading marker/cursor displayed on the RADAR scope that changes automatically as
the ship changes course.
The RADAR repeaters used aboard ship have the same features as those used ashore:
variable range control, off-center sweep and cursor, and range marks.
Precision Approach and Landing System
Precision approach and landing system (PALS) (formerly called the Automatic Carrier
Landing System) includes the AN/SPN-46 and associated systems that enable pilots to
perform precision instrument approaches to the aircraft carrier. To provide continuous
capability to the pilot and controllers, PALS has a precision tracking RADAR that is
coupled to a computer data link.
PALS Modes of Operation
PALS have three general types of control. They differ on the basis of type of control
(automatic or manual) and source of information (display or voice):
Fully automatic approach (Mode I/IA)
Manual controlled approach with PALS glide slope and lineup information
provided by pilot cockpit display (Mode II/IIT)
Conventional manual CCA in which the controller provides glide slope, azimuth,
and range information by voice (Mode III)
AN/SPN-46
The AN/SPN-46 has two consoles, each of which can track (lock on) two aircraft at a
time. The SPN-46 also interfaces with the CATCC DAIR. This interface is used to select
the display of aircraft being tracked by the CATCC DAIR. This interface causes aircraft
symbols and side numbers of DAIR-tracked aircraft to appear on the console display.
Automatic Landing System
Besides providing precision tracking RADAR, the AN/SPN-46 has the capability of
providing a completely automatic landing. When an aircraft approaches a carrier, the
precision tracking RADAR monitors the aircraft's progress and feeds the position
information to a computer. The computer measures the aircraft's position in relation to a
preselected approach path. To maneuver the aircraft to the desired path, the computer
determines what corrections are necessary. The corrections are then transmitted by
radio to the aircraft. Equipment in the aircraft feeds the commands through an autopilot
5-49
