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S-based technologies are described below.
TRAFFIC ALERT AND
COLLISION AVOIDANCE SYSTEM
The traffic alert and collision avoidance system (TCAS)
is designed to provide a set of electronic eyes so the pilot
can maintain awareness of the traffic situation in the
vicinity of the aircraft. The TCAS system uses three separate systems to plot the positions of nearby aircraft.
First, directional antennae that receive Mode S transponder signals are used to provide a bearing to neighboring
aircraft ⎯ accurate to a few degrees of bearing. Next,
Mode C altitude broadcasts are used to plot the altitude
of nearby aircraft. Finally, the timing of the Mode S
interrogation/response protocol is measured to ascertain
the distance of an aircraft from the TCAS aircraft.
TCAS I allows the pilot to see the relative position and
velocity of other transponder-equipped aircraft within a
10 to 20-mile range. [Figure 1-14] More importantly,
TCAS I provides a warning when an aircraft in the vicinity gets too close. TCAS I does not provide instructions
on how to maneuver in order to avoid the aircraft, but
1-21
does supply important data with which the pilot uses to
evade intruding aircraft.
TCAS II provides pilots with airspace surveillance,
intruder tracking, threat detection, and avoidance
maneuver generations. TCAS II is able to determine
whether each aircraft is climbing, descending, or flying
straight and level, and commands an evasive maneuver to
either climb or descend to avoid conflicting traffic. If both
planes in conflict are equipped with TCAS II, then the
evasive maneuvers are well coordinated via air-to-air
transmissions over the Mode S datalink, and the commanded maneuvers do not cancel each other out.
TCAS and similar traffic avoidance systems provide
safety independent of ATC and supplement and enhance
ATC’s ability to prevent air-to-air collisions. Pilots currently use TCAS displays for collision avoidance and
oceanic station keeping (maintaining miles-in-trail separation). Recent TCAS technology improvements enable
aircraft to accommodate reduced vertical separation
above FL 290 and the ability to track multiple targets at
longer ranges. The Airborne Collision Avoidance
System (ACAS) is an international ICAO standard that
is the same as the latest TCAS II, which is sometimes
called “Change 7” or “Version 7” in the United States.
ACAS has been mandated, based on varying criteria,
throughout much of the world.
TRAFFIC INFORMATION SERVICE
Traffic Information Service (TIS) provides many of the
functions available in TCAS; but unlike TCAS, TIS is
a ground-based service available to all aircraft
equipped with Mode S transponders. TIS takes advantage of the Mode S data link to communicate collision
avoidance information to aircraft. Information is pre-
sented to a pilot in a cockpit display that shows traffic
within 5 nautical miles and a 1,200-foot altitude of
other Mode S-equipped aircraft. The TIS system uses
track reports provided by ground-based Mode S surveillance systems to retrieve traffic information.
Because it is available to all Mode S transponders, TIS
offers an inexpensive alternative to TCAS. The increasing
availability of TIS makes collision avoidance technology
more accessible to the general aviation community.
Beginning in 2005, the use of Mode S TIS is being discontinued at some sites as the ground radar systems are
upgraded. In all, 23 sites are expected to lose TIS capability by 2012.
TERRAIN AWARENESS AND WARNING SYSTEM
The Terrain Awareness and Warning System (TAWS) is
an enhanced ground proximity warning capability being
installed in many aircraft. TAWS uses position data from
a navigation system, like GPS, and a digital terrain database to display surrounding terrain. TAWS equipment is
mandatory for all U.S registered turbine powered airplanes with six or more passenger seats. FAA and NTSB
studies have shown that a large majority of CFIT accidents could likely have been avoided had the aircraft
been equipped with enhanced ground proximity warning systems.
GRAPHICAL WEATHER SERVICE
The Graphical Weather Service provides a graphical representation of weather information that is transmitted to
aircraft and displayed on the cockpit display unit. The
service is derived from ground-based Mode S sensors
and offers information to all types of aircraft, regardless
of the presence of on-board weather avoidance equipment. The general aviation community has been very
pro-active in evaluating this technology, as they have
already participated in field evaluations in Mode S stations across the U.S. The service is provided through
　
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本文鏈接地址：Instrument Procedures Handbook (IPH)儀表程序手冊上(30)