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FLIGHT THEORY
Konu: 8.Visual Navigation Fundamentals
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Global Positioning Systems (GPS)
Precise point-to-point navigation is possible using satellite navigation systems that
can compute aircraft position and altitude accurately by comparing signals from a
global network of navigation satellites. The first global positioning systems (GPS) were
designed for the U.S. Department of Defense, but in the early 1990s, GPS was made
available for civilian use. Later, full system accuracy was also made available.
Basically, three elements make up GPS:
1. a space element, consisting of a constellation of satellites orbiting the earth every
12 hours in six orbital planes, at an altitude of 11,000 NM (21,300 km);
2. a satellite control ground network responsible for orbital accuracy and control; and
3. a navigation receiver in the aircraft (many are small enough to be hand held)
capable of receiving and identifying several satellites at a time.
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Radar & ADS-B
In the high-volume traffic environment of today’s airspace, radar is the primary tool
used by Air Traffic Control to provide many vital services to IFR (and VFR) aircraft,
such as radar vectoring, radar separation and sequencing. The air traffic controller is
presented with an electronic map of the area of responsibility, showing the position of
aircraft within it. Among the advantages of this system are:
• reduced air-ground radio communication; for instance, there is no need for a pilot
to transmit regular position reports;
• an ability to handle an increased number of aircraft in the same volume of airspace,
with reduced, but still safe, separation distances;
• an ability to radar vector an aircraft along any desired course by passing headings to
steer directly to the pilot; and
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Using the Transponder
Most aircraft are equipped with a transponder (XPDR) that transmits a strong
responding signal to a secondary ground radar, which can provide ATC with additional
information such as aircraft identification and altitude. The theory of secondary
surveillance radar (SSR or ATCRBS) is discussed in detail at the end of this chapter.
The operating techniques are considered here.
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How Radar Works
The remainder of this chapter discusses the basic theory of radio waves, and of radar
in particular. It is not essential knowledge but it will help your understanding of radio,
radar and NAVAIDs.
Radio utilizes the ability to transmit electromagnetic energy, in the form of radio
waves, from one place to another. Radio has played a vital role in the development of
aviation — radar is an important type of radio system.
Waves of electromagnetic energy emanating from a radio transmitter can carry
information, such as speech, music, and Morse code out into the surrounding environment.
Radio receivers tuned to the same frequency may detect and utilize these
signals, often at quite long distances from the transmitter.
Important aeronautical uses of radio include:
• air/ground voice communication;
• navigation (the ADF/NDB combination, VOR and ILS); and
• radar.
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Traffic Awareness and Collision Avoidance Systems
There are several devices now available to alert pilots of potentially conflicting traffic
and the risk of collision. They work on one of two principles:
• active; and
• passive.
They use the same principle as SSR. The aircraft carries a device that receives
other airborne transponders. The active systems do not rely on ground radar to trigger
those airborne transponders. The aircraft carries its own interrogator. Passive
systems rely on the SSR to trigger a response, and they therefore only work within
ground radar coverage. In the U.S. where there is extensive radar coverage, the simple
and more economical passive systems work very well.
Active Systems
TCAS I Systems
TCAS II Systems
Passive Systems (TCAD, TPAS and ATD)
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Weather Detection and Avoidance
Weather alerting devices also use active and passive modes to detect and classify
significant weather. The active systems use a radar transmitter/receiver. The passive
systems detect electrical charges and discharges in the atmosphere (lightning).
These two types of systems for detection and avoidance of hazardous weather are
quite different in their principles of operation. They are:
• weather radar; and
• stormscopes.
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