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flight planning within published guidelines. The Free
Flight program allows dispatchers and pilots to choose
the most efficient and economical route for flights operating at or above FL 290 between city pairs, without
being constrained to airways and preferred routes.
Free Flight is a concept that allows you the same type of
freedom you have during a VFR flight. Instead of a NAS
that is rigid in design, pilots are allowed to choose their
own routes, or even change routes and altitudes at will
to avoid icing, turbulence, or to take advantage of
winds aloft. Complicated clearances become unnecessary, although flight plans are required for traffic planning purposes and as a fallback in
the event of lost communication.
Free Flight is made possible with
the use of advanced avionics, such
as GPS navigation and datalinks
between your aircraft, other aircraft, and controllers. Separation is
maintained by establishing two airspace zones around each aircraft, as
shown in Figure 6-12. The protected zone, which is the one closest to the aircraft, never meets the
protected zone of another aircraft.
The alert zone extends well beyond
the protected zone, and aircraft can
maneuver freely until alert zones
touch. If alert zones do touch, a
controller may provide the pilots
with course suggestions, or
onboard traffic displays may be
used to resolve the conflict. The size of the zones is
based on the aircraft’s speed, performance, and equipment. Free Flight is operational in Alaska, Hawaii, and
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
　
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