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traffic requirements in addition to weapon system employment. To handle these conditions at high
speeds more effectively, the navigator uses a navigation system.
16.3. Types of Systems. Navigation systems can be classified according to many criteria. Systems can
be classified by capability such as VFR-only or all-weather. They can be classified by mission type such
as ground-attack, air-to-air, or combat support. They can be classified as either self-contained or
externally-referenced. They may also be classified as to whether they emit signals or are passive. Each
system has advantages and disadvantages, but we will confine this discussion to self-contained and
externally referenced systems.
16.3.1. Self-Contained Navigation Systems. Self-contained systems (radar, celestial, INS) are complete
in that and they do not depend upon externally transmitted data. Weapon systems equipped with selfcontained
navigation systems can operate anywhere in the world without the assistance of ground- or
space-based transmitters.
16.3.2. Externally-Referenced Navigation Systems. Externally-referenced aids (GPS, NAVAIDs)
include all aids that depend upon transmission of energy or information from an external source to the
aircraft. Externally-referenced navigation systems provide information to anyone, which in time of war
includes the enemy as well as friendly forces. Another disadvantage of externally-referenced aids is their
vulnerability to attack, jamming, or exploitation. While externally referenced aids have enormous
installation and operating costs to the system administrator, they have much lower equipment and
maintenance costs to the user.
AFPAM11-216 1 MARCH 2001 327
16.4. The Ideal System. Every navigation system has certain advantages and disadvantages. A
particular navigation system is selected for use in an aircraft when its advantages outweigh its
disadvantages. In some cases, several components are included in a system to provide adequate,
redundant information for all possible mission taskings. The ultimate navigation system should have the
following characteristics:
16.4.1. Groundplot DR Information. The system must indicate the position and velocity relative to the
ground.
16.4.2. Global Coverage. Capable of positioning and steering the aircraft accurately and reliably any
place in the world.
16.4.3. Self-Contained. It must not rely on ground or space transmissions of any kind.
16.4.4. Passive Operation. It must not betray the position of the aircraft by transmitting signals of any
kind.
16.4.5. Immune to Countermeasures. The system must not be susceptible to countermeasures of any
type.
16.4.6. Useless to Enemy. It must not provide navigation information or intelligence of any kind to
enemy forces.
16.4.7. Flexible. Works well despite unplanned deviations. The system must work well at all altitudes
and speeds.
16.5. Components. The navigational system consists of three parts: (1) the computer or central
processing unit (CPU), (2) data-gathering sensors like astrotrackers, GPS, ground mapping radar, or
NAVAIDS; and (3) an operator input/output (I/O) interface. The CPU takes in all available data and
converts it into usable navigation information. Control panels or computer keyboards allow the operator
to control and make inputs to the computer. Data is displayed for the operator on display panels, radar
screens, or computer screens. Additional software components might be capable of air-to-ground
delivery, air-to-air intercepts, weapons employment, threat avoidance, and rendezvous. Additional
hardware components could include terrain following radar, television cameras, or threat detection
receivers.
16.6. Computer Unit. Most navigation systems are hybrids of the two basic computer types: analog and
digital.
16.6.1. Analog. Analog computers are more specific in design and function than digital computers.
While analog computers process vast amounts of similar data they are not very flexible and cannot be
used for multiple purposes. Radar scan converters efficiently process collected radar signals into video
images. Video processors collect and process images into video displays. Other examples of analog
computers are terrain-avoidance computers and terrain-following computers.
16.6.2. Digital. Digital computers are lighter and more compact than analog computers. Hand-held
calculators and laptop computers are two examples of the miniaturization possible with digital
computers. You can put a great deal of computing power and capability into a small box; the biggest
328 AFPAM11-216 1 MARCH 2001
limitation is increased cost. An analog radar scan converter is very efficient at processing radar data, but
it cannot be used for other applications. On the other hand, digital computers can be loaded with
　
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