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part of the Pacific Ocean, using about 2,000 aircraft. Full
implementation is projected to take about 20 years.
As the FAA and industry work together, the technology
to help Free Flight become a reality is being placed into
position, especially through the use of the GPS satellite
system. Equipment such as ADS-B allows pilots in their
cockpits and air traffic controllers on the ground to “see”
aircraft traffic with more precision than has previously
been possible. The FAA has identified more than 20
ways that ADS-B can make flying safer. It can provide a
more efficient use of the airspace and improve your situational awareness.
DEVELOPING TECHNOLOGY
Head-up displays (HUDs) grew out of the reflector
gun sights used in fighter airplanes before World War
II. The early devices functioned by projecting light
onto a slanted piece of glass above the instrument
panel, between the pilot and the windscreen. At first,
the display was simply a dot showing where bullets
would go, surrounded by circles or dots to help the
pilot determine the range to the target. By the 1970s,
the gun sight had become a complete display of flight
information. By showing airspeed, altitude, heading,
and aircraft attitude on the HUD glass, pilots were
able to keep their eyes outside the cockpit more of the
time. Collimators make the image on the glass appear
to be far out in front of the aircraft, so that the pilot
need not change eye focus to view the relatively
nearby HUD. Today’s head-up guidance systems
(HGS) use holographic displays. Everything from
weapons status to approach information can be shown
on current military HGS displays. This technology has
Figure 6-11. Prototype Data Link Equipment. This display
shows a radar image of weather within 50 NM of the Seattle-
Tacoma International Airport (KSEA).
Figure 6-12. Free Flight.
6-13
6-14
obvious value for civilian aviation, but until 1993 no
civilian HGS systems were available. This is changing, and application of HGS technology in airline and
corporate aircraft is becoming widespread.
[Figure 6-13]
A large fraction of aircraft accidents are due to poor
visibility. While conventional flight and navigation
instruments generally provide pilots with accurate
flight attitude and geographic position information,
their use and interpretation requires skill, experience,
and constant training. NASA is working with other
members of the aerospace community to make flight
in low visibility conditions more like flight in visual
meteorological conditions (VMC). Synthetic vision
is the name for systems that create a visual picture
similar to what the pilot would see out the window in
good weather, essentially allowing a flight crew to see
through atmospheric obscurations like haze, clouds,
fog, rain, snow, dust, or smoke.
The principle is relatively simple. GPS position information gives an accurate three-dimensional location,
onboard databases provide detailed information on terrain, obstructions, runways, and other surface features,
and virtual reality software combines the information to
generate a visual representation of what would be visible
from that particular position in space. The dynamic image
can be displayed on a head-down display (HDD) on the
instrument panel, or projected onto a HGS in such a way
that it exactly matches what the pilot would see in clear
weather. Even items that are normally invisible, such as
the boundaries of special use airspace or airport traffic
patterns, could be incorporated into such a display. While
the main elements of such a system already exist, work is
continuing to combine them into a reliable, safe, and practical system. Some of the challenges include choosing the
most effective graphics and symbology, as well as making
the synthetic vision visible enough to be useful, but not so
bright that it overwhelms the real view as actual terrain
becomes visible. Integrating ADS-B information may
make it possible for synthetic vision systems to show
other aircraft. [Figure 6-14]
A natural extension of the synthetic vision concept is the
highway in the sky (HITS) program. This technology
adds an easy-to-interpret flight path depiction to an electronic flight instrument system (EFIS) type of cockpit
display, which may be located on the instrument panel
or projected on a HUD. The intended flight path is
shown as a series of virtual rectangles that appear to
stand like a series of window frames in front of the aircraft. The pilot maneuvers the aircraft so that it flies
“through” each rectangle, essentially following a visible
　
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