Head-Up Display (HUD)

The HUD is a display system that provides a projection of
navigation and air data (airspeed in relation to approach
reference speed, altitude, left/right and up/down GS) on a
transparent screen between the pilot and the windshield. Other
information may be displayed, including a runway target in
relation to the nose of the aircraft. This allows the pilot to see
the information necessary to make the approach while also
being able to see out the windshield, which diminishes the
need to shift between looking at the panel to looking outside.
Virtually any information desired can be displayed on the
HUD if it is available in the aircraft's flight computer, and
if the display is user definable. [Figure 7-44]

Figure 7-44. Example of a Head-Up Display (top) and a
Head-Down Display (bottom). The head-up display presents
information in front of the pilot along his/her normal filed of view
while a head-down display may present information beyond the
normal head-up field of view.

Radar Navigation (Ground Based)

Radar works by transmitting a pulse of RF energy in a specific
direction. The return of the echo or bounce of that pulse from
a target is precisely timed. From this, the distance traveled
by the pulse and its echo is determined and displayed on a
radar screen in such a manner that the distance and bearing to
this target can be instantly determined. The radar transmitter
must be capable of delivering extremely high power levels
toward the airspace under surveillance, and the associated
radar receiver must be able to detect extremely small signal
levels of the returning echoes.

The radar display system provides the controller with a map-
like presentation upon which appear all the radar echoes
of aircraft within detection range of the radar facility. By
means of electronically generated range marks and azimuth-
indicating devices, the controller can locate each radar target
with respect to the radar facility, or can locate one radar target
with respect to another.

Another device, a video-mapping unit, generates an actual
airway or airport map and presents it on the radar display
equipment. Using the video-mapping feature, the air traffic
controller not only can view the aircraft targets, but also can see
these targets in relation to runways, navigation aids, and
hazardous ground obstructions in the area. Therefore, radar
becomes a NAVAID, as well as the most significant means
of traffic separation.

In a display presenting perhaps a dozen or more targets, a
primary surveillance radar system cannot identify one specific
radar target, arid it may have difficulty 'seeing" a small target
at considerable distance - especially if there is a rain shower
or thunderstorm between the radar site and the aircraft. This
problem is solved with the Air Traffic Control Radar Beacon
System (ATCRBS), sometimes called secondary surveillance
radar (SSR), which utilizes a transponder in the aircraft. The
ground equipment is an interrogating unit, in which the beacon
antenna is mounted so it rotates with the surveillance antenna.
The interrogating unit transmits a coded pulse sequence that
actuates the aircraft transponder. The transponder answers die
coded sequence by transmitting a preselected coded sequence
back to the ground equipment, providing a strong return signal
and positive aircraft identification, as well as other special data
such as aircraft altitude.

Functions of Radar Navigation
The radar systems used by ATC are air route surveillance
radar (ARSR). airport surveillance radar (ASR), and precision
approach radar (PAR) and airport surface detection equipment
(ASDE). Surveillance radars scan through 360° of azimuth
and present target information on a radar display located in
a tower or center. This information is used independently or
in conjunction with other navigational aids in the control of
air traffic.