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هل من يشرح لي و يعطيني لمحة عن هذا النظام الملاحي : Tls ؟؟؟ Tranponder Landing System



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[DUBAI ATCO]

عليكم السلام ورحمة الله وبركاته

A New Approach Using Familiar Radios
by Gary Picou

Airplanes are supposed to take people where they want to go. If where they want to go is in a small town and under the weather, airplanes can't get there. That situation is changing rapidly. There are at least two schemes around. GPS or Differential Global Positioning System (DGPS) is one idea that uses our celestial radionavigation system. Coupled with new and exotic gear in the cockpit it can make a near CAT 1 (or better) approach into remote locations.

Just when you think that the world is looking to orbit for all their needs, a company hands you a very Earthly mousetrap that is elegant, simple, effective and affordable. Advanced Navigation and Positioning Corp. is a company that has such a rodent snare. Precision instrument approaches into airports without the hectares of vacant ground around them, or airports without the economic benefit of thousands of flights each day.

This system is the Transponder Landing System, developed by Advanced Navigation and Positioning Corp. of Hood River, Ore. The concept is simple, the ground installation easy, and the potential applications are endless.

The Problems

The conventional Instrument Landing System has been around for a very long time. According to the book "Manual of Avionics", ILS was developed in 1946, and was finally deemed completely developed in 1973, when the solid state systems were deployed.

We all know that the current ILS transmits a VHF localizer and UHF glideslope signal, modulated with 150 and 90 Hz audio tones. The modulation of these tones provides a measure of the deviation from the extended centerline of the runway, and a 3-degree sloped beam ending at about the runway threshold.

By the very nature of the signals, the approach must be straight, and the landscape over which the beam passes must be electrically compatible with UHF and VHF Amplitude Modulation. By the time you invest in the electronics, real estate and illumination, you've spent well over a million dollars just for the installation. Then it must be maintained.

As a result, the number of ILS-equipped runways is relatively small--about 1,000, compared to the more than 5,700 public airports in the United States. If you figure that each of those airports has two possible approaches, at least 91 percent of the runways do not have an ILS.

System Description

The Transponder Landing System is so very simple in design to be among the more elegant solutions in this world. Here is how the system works. Ground stations interrogate the standard ATCRBS Transponder. The replies are received by an antenna array that processes the signals and determines the position and altitude of the aircraft within the airport traffic area (actually out to about 22 nm). Altitude is independent of Mode C; the 3-D position is derived from the received signals much like a DF.

Once the TLS has the position information, it transmits a signal to the aircraft that provides steering on the localizer and glideslope to touchdown. This can be curved, dog leg, step down--you name it. The ultimate goal is to steer the aircraft from where it is to the runway.

Where a conventional ILS send out a fixed beam that the pilot aligns himself with, TLS actually adjusts the beam to bring in the airplane. In the cockpit. the instrument presentation is the same, just keep the needles centered.

Origins

John Stoltz, president, CEO and chairman of the board for Advanced Navigation and Positioning Corp. is the brains behind the system. A military aerospace engineer, Stoltz stayed in the West when the F22 program moved east, preferring the peaceful Northwest to the packed Northeast.

When he contemplated leaving the world of military aviation, he had to see a future for the civil aviation industry. In his vision he saw 17,000 under-served airports, and 130,000 (by FAA account) aircraft equipped with conventional localizer and glideslope systems. His vision was cloudy when it came to Microwave Landing Systems, LAAS and WAAS DGPS systems. He could see the many popular resort destinations, like Sun Valley, Idaho, losing customers because of difficult access by air (with impossible access by land).

The idea to put the existing systems together in a new way was first hatched in the early 90s, and in 1992, Advanced Navigation and Positioning Corp. was launched to make it happen. In these last six years the system has worked and been proven ever more robust in many situations. Systems have been installed in Madras Ore., (south of the ANPC headquarters in Hood River) and at Watertown, Wis., where the EAA dignitaries can see the system in operation.

The next fully commissioned system won't be in the United States, however. Federal Express has a system installation at Subic Bay, The Philippines, to serve the Asian hub. The terrain makes the approach ILS unfriendly; yet for FedEx, it absolutely, positively must be accessible.

In fact, Stoltz says that internationally the TLS market could be two to three times as large as the United States. The system can be delivered in a crate, set up and certified very easily. There are no site problems and the system is self contained. Add a generator and the system can provide precision approach capability into any village, anywhere. Nepal? Stoltz has done that, in an A300 with a six-degree glideslope.

One of the beauties of the TLS system, from Stoltz's view, is that the documentation already exists. The FAA and ICAO are familiar with what it takes on the aircraft side for an ILS approach. The TERPS (terminal instrument flight procedures) are commonly used.

System details

There are few components in the TLS system. The most visible are four units mounted in a 50 meter radius alongside the runway. There is a base station unit. a Calibration/Built-in-Test (BIT) unit that monitors station accuracy and integrity, and two angles of arrival antennas. The localizer and glideslope angle of arrival AOA sensors are used to define the flightpath from the transponder system as it nears the runway.

A central processor in the base station computes the aircraft position in three dimensions, calculates where it should be in relation to the approach, and transmits corrections to the aircraft over the localizer and glideslope transmitter.

Because the system can be programmed precisely for the location, the approach can be curves, segmented, dogleg, or whatever is necessary to avoid any obstacle along the approach path. These obstacles, can be political, too. Some airports are considering TLS as a way to avoid noise sensitive areas on the approach.

The glideslope is adjustable as well. Some airports, like Aspen, want a steep glidepath. For helicopters anyway, even steeper approaches are possible.

The basic TLS can provide guidance in an area that extends 45 degrees from the runway centerline. However, we think most airports would opt for some additional receivers that would extend the service area to 360 degrees around the runway , and 22 miles out.

The system is capable of tracking 25 aircraft (or even equipped ground vehicles as a way to prevent runway incursion accidents). One of the limitations of a single TLS system is that only one aircraft could be "on the beam" at a time, because the TLS generates a correction based on its position. However, the system isn't intended to replace the ILS at Denver International or DFW, with the constant parallel approaches. The TLS is a low traffic volume system.

CFIT

Since the TLS is smarted than the average beam, it can easily keep the pilot and aircraft out of trouble with the terrain. In recent history, Controlled Flight into Terrain (CFIT) has accounted for a staggering 50 percent of the air transport fatalities. With TLS, terrain avoidance is natural, because the system is communicating directly with the airplane on the approach. It knows the displacement from the runway, as well as the obstructions. The monitoring and safety functions are inherent in the TLS, and don't have to be fitted into the cockpit, like the Enhanced GPWS systems.

GPS?

If the FAA is so set on having GPS approaches available for the masses, where does the TLS fit in? According to Stoltz, it fits perfectly as a combination second source back-up and integrity monitor. Adding differential correction and data link capability, particularly with the Mode S transponders that will be available, the TLS can provide corrections as well as approach guidance. As a monitor, it can take over at a moment's notice if the constellation should lose integrity. In the sorts of areas where the TLS thrives, mountainous and obstructed, the GPS constellation doesn't have the horizon to horizon view it ought to have for signal availability. As a local system, the TLS is impervious to the problems associated with pushing a 1.5 GHz signal across 11,000 miles.

Military applications

As you might imagine, the military loves TLS. The whole thing can be loaded up in a HMMMWV (that's "hummvee" to you and me), delivered with a towed generator, set up by two men, and provide CAT I approaches to a dirt strip in four hours. Such a system, if deployed by the military in Dubrovnik, Croatia, could have prevented the crash that killed Secretary of Commerce Ron Brown, and all who perished on that flight.

Since the system is capable of data link, it offers lots of battlefield tactical capabilities that we don't have to know about. One important capability though involves non-ILS equipped aircraft. While most military aircraft carry conventional ILS systems, some, like the Marine AV-8B Harriers, don't. For an airplane with 90-degree approach capability, perhaps a three-degree glideslope is a bit silly. Instrument approaches in these aircraft types are made using Precision Approach Radar (PAR). This is where a ground operator "talks down" the airplane. With TLS, it is just as easy as the conventional system. An operator reads the position display, and relays guidance to the pilots as before. Like the TLS, the cockpit environment doesn't change, only the ground segment. In this case, a powerful PAR radar system is not required.

The military transportable TLS was developed on a Defense Advanced Research Projects Agency (DARPA) contract and was tested at an exercise on January 20, 1998. The USAF, USMC and Navy flew examples of every kind of aircraft against the TLS. Besides Harriers, there were helicopters, fighters and transports. They made straight approaches, they made curved approaches, and they made steep approaches. The boys with brass buttons were pleased and satisfied.

Future expansions

The future is bright for the TLS, especially as the WAAS image in the crystal ball grows cloudier. Besides the Subic Bay installation Advanced Navigation and Positioning Corp. plans to deploy the system in Seattle at Boeing Field, Sun Valley, Naples Fla. and internationally in Guatemala City as well as Tegucigalpa Honduras, to name a few.

We mentioned the data link capability of the system. The sky is virtually the limit for data link applications, but a few would be traffic and ground surveillance in the terminal area, remote traffic monitoring by ATC, messages transfer, and other military-related applications.

Take care of those localizer and glideslope systems, folks. They may be with us for a long time, and be much more useful in the future.

Note: This article has been reprinted with the permission of AVIONICS NEWS magazine, a monthly publication of the Aircraft Electronics Association.

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