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RobbieHe

Backcourse Mode

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Can someone please explain in plain English what the backcourse mode is for? I primarily use LDS-767 in Fs2004, not that it matters. But, in what situations do pilots use the backcourse mode? How important is it?RH

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Can someone please explain in plain English what the backcourse mode is for? I primarily use LDS-767 in Fs2004, not that it matters. But, in what situations do pilots use the backcourse mode? How important is it?RH
For a somewhat humerous but accurate explaination of what a backcourse is (with illustrations), try this link:http://stoenworks.com/Tutorials/ILS%20Back...Approaches.htmlI found it of value - hope you do also.

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The "localizer" portion of an ILS contains an array of antenna elements. The design of the elements is intended to produce a directional radio signal, with maximum radiated power in the direction of the runway centerline (or offset course if the localizer is not aligned with the runway). The nature of the antenna is that most of the radiated power is in one direction, termed the front or front course, but some signal will also radiate in the opposite direction, termed the backside or back course. The amount of radiated power in the back direction depends on the antenna element design. The older localizer antenna design still in service in some locations are termed v-loop, based on their appearance, and these transmit a significant back course signal. The more common (and modern) antenna elements are log-periodic, and these have a feature that not nearly as much power is radiated on the back course.With a sensitive enough receiver, the back side signal could probably be received at any localizer. The FAA and other certifying agencies don't test or approve the use of the back signal, except in certain instances. In these cases there will be a published approach procedure/SIAP for the backcourse. Limmitations in the approach should be adhered to, since even though the approach is published, in general the backcourse "service volume" (i.e., distance in which the signal is certified as valid) is less than the standard 25nm (ICAO) or 18nm (FAA) for a localizer.In FS MS only modeled the localizer with a "backcourse available" switch, with all default localizers having the switch set. I haven't really tested it, but I suspect the back course side of a localizer has the same range as the front course in FS. Note that the localizer is designed to radiate on the main frequency as listed on the charts, and the carrier is modulated by two different frequencies (from memory 90 and 150 Hz). The two modulations are decoded by the aircraft receiver, and the difference in amplitude of the signals causes the deviation needle or OBI to deflect left or right. Since the general rule of thumb is to turn towards the needle, when following the backcourse it is necessary to get the needle to deflect in the opposite direction for the rule of thumb to be valid, hence the "backcourse mode".scott s..

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Thanks for the explanation! I have copied and saved it in a word file in hopes of one day actually understanding what the everyday function of it is.RH

The "localizer" portion of an ILS contains an array of antenna elements. The design of the elements is intended to produce a directional radio signal, with maximum radiated power in the direction of the runway centerline (or offset course if the localizer is not aligned with the runway). The nature of the antenna is that most of the radiated power is in one direction, termed the front or front course, but some signal will also radiate in the opposite direction, termed the backside or back course. The amount of radiated power in the back direction depends on the antenna element design. The older localizer antenna design still in service in some locations are termed v-loop, based on their appearance, and these transmit a significant back course signal. The more common (and modern) antenna elements are log-periodic, and these have a feature that not nearly as much power is radiated on the back course.With a sensitive enough receiver, the back side signal could probably be received at any localizer. The FAA and other certifying agencies don't test or approve the use of the back signal, except in certain instances. In these cases there will be a published approach procedure/SIAP for the backcourse. Limmitations in the approach should be adhered to, since even though the approach is published, in general the backcourse "service volume" (i.e., distance in which the signal is certified as valid) is less than the standard 25nm (ICAO) or 18nm (FAA) for a localizer.In FS MS only modeled the localizer with a "backcourse available" switch, with all default localizers having the switch set. I haven't really tested it, but I suspect the back course side of a localizer has the same range as the front course in FS. Note that the localizer is designed to radiate on the main frequency as listed on the charts, and the carrier is modulated by two different frequencies (from memory 90 and 150 Hz). The two modulations are decoded by the aircraft receiver, and the difference in amplitude of the signals causes the deviation needle or OBI to deflect left or right. Since the general rule of thumb is to turn towards the needle, when following the backcourse it is necessary to get the needle to deflect in the opposite direction for the rule of thumb to be valid, hence the "backcourse mode".scott s..
Thanks! I have saved the link.RH
For a somewhat humerous but accurate explaination of what a backcourse is (with illustrations), try this link:http://stoenworks.com/Tutorials/ILS%20Back...Approaches.htmlI found it of value - hope you do also.

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If you are talking about a button on your autopilot, or a mode setting in the FMC, the purpose is to tell the autopilot that it needs to track the back course of a localizer. If the autopilot doesn't know it is tracking a back course, it will turn away from the track when it needs to turn toward the track.The back course mode is used only when making a back course approach. That means using a ILS localizer from the direction opposite it was designed to be used. Defining a back course approach saves the facility the cost of installing another set of equipment for an approach from the opposite direction. If you are hand flying a back course approach, "back course mode" has to be operating in your head, not as a mode in the autopilot. Turn away from the needle to center it.

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