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Why use TACAN when ILS is available


tangodownNZ
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The areas of coverage are different. ILS only works along the extended centerline of the runway, while TACAN is omni-directional. For instance, if you're 100nm south of an airport with runways easy/west (09/27), you'd typically use enroute navaids like TACAN or VOR+DME (the civilian equivalent) to find the area where you can intercept the localizer, and then continue on an ILS approach/landing from there.

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For the specially interested, here is a diagram showing the specified localizer coverage in the horizontal plane for FAA (right) and ICAO (left).

 

The light green ±10° area is the main course guidance signal, while the dark green ±35° area is the clearance signal, which basically just gives you a full FLY RIGHT or FLY LEFT indication in the CDI until you intercept the main course signal.

 

attachment.php?attachmentid=170289&stc=1&d=1507149595

(diagram borrowed from an old Norwegian CAA handbook)

1394573997_ilscoverage.PNG.83eb59bac56edd415e134a627075d34a.PNG

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In real life things breakdown. You need more than one navigational aid to insure you can land at an airport. Also, many airports don't have ILS.

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TACAN or VOR+DME is not a backup for ILS. These systems can guide you down to visual minima, but they are not landing aids, as they do not provide any horizontal or vertical guidance signals for landing. Simply put, they can help you find the airport, but if you can't see the runway lights when you get down to the decision height for non-precision approaches, you'll need to find somewhere else to land.

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TACAN is an area navigation facility. ILS is a landing aid. ILS is never, ever used by itself.

 

You see most simulation pilots treat ILS as sole reference blindly wandering into the beams with an improvised technique. This is not how it is done in reality.

 

As far as that single vector you get from the automated ATC on initial contact, it's of low quality. There is no terrain or traffic clearance, no monitoring, no allowance for wind, turn radius, or even magnetic variation. If the turns can be approximated by 0 radius and the other problems are avoided then this vector can suffice to steer you into the beams. The real life analog is radar vectors to intercept no later than FAF.

 

The bearing pointer in the A-10 does not point toward the ILS. Maybe you have bearing to an INS waypoint which is at the same place but this is a coincidence. No part of the ILS gives bearing information.

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TACAN is an area navigation facility. ILS is a landing aid. ILS is never, ever used by itself.

 

You see most simulation pilots treat ILS as sole reference blindly wandering into the beams with an improvised technique. This is not how it is done in reality.

 

As far as that single vector you get from the automated ATC on initial contact, it's of low quality. There is no terrain or traffic clearance, no monitoring, no allowance for wind, turn radius, or even magnetic variation. If the turns can be approximated by 0 radius and the other problems are avoided then this vector can suffice to steer you into the beams. The real life analog is radar vectors to intercept no later than FAF.

 

The bearing pointer in the A-10 does not point toward the ILS. Maybe you have bearing to an INS waypoint which is at the same place but this is a coincidence. No part of the ILS gives bearing information.

You are right! I was using the divert page which automatically creates a waypoint. I thought that was ILS doing that.

 

Thanks everyone.

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Decision Height (DH) is used for ILS precision approaches while Minimum Descent Altitude (MDA) is used for non-precision approaches, (TACAN, LOC, VOR, ILS with G/S out).

 

Thanks for the correction regadring MDA. Being in the ILS business, I just automatically think and speak in "ILS terms".

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  • 1 month later...
Thanks for all the helpful info. But I can be way off the center line of the runway like perpendicular and 20Nm out and my bearing pointer still points to the airfield with only ILS, no TACAN. Thats why I thought whats the point of TACAN

 

Learn the use the full capabilities of the HSI, specifically the CDI in conjunction with setting a course using the course knob.

 

Spoiler

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The real ILS does not give you bearing to station, only localizer and glideslope deviation. If you see bearing to station then it's a bug in DCS. Or the bearing info comes from different system.

 

The ILS itself also does not give you range to the station, but it is usually collocated with VOR/DME or TACAN station, so the range readout comes from that.

 

In real life it's also highly directional and sensitive to obstructions. Not usable for area navigation.

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The real ILS does not give you bearing to station, only localizer and glideslope deviation. ......

 

....The ILS itself also does not give you range to the station, but it is usually collocated with VOR/DME or TACAN station, so the range readout comes from that.

 

Let’s be more precise. ILS stands for instrument landing system. It’s purpose is to provide alignment and descent on final approach to a runway.

 

It has three parts.

 

The first is GUIDANCE INFORMATION. These are mainly what you guys have been talking about... both localizer and glideslope.

 

The second is RANGE INFORMATION. This would be from a marker beacon or DME.

 

The third is VISUAL INFORMATION. Approach lights, centerline and touchdown lights, and runway lights.

 

DME can be installed with the ILS and be part of the associated procedure (e.g., ILS or LOC/DME Rwy 11). If this is the case then DME can substitute for the OM, BC FAF, or other fixes along the localizer path).

 

It would be incorrect to suggest DME is typically only from VOR or TACAN.

 

Also, another compenent of the ILS, the Outer Marker, can provide the FAF for non precision approaches using the localizer. So, we actually do use ILS components to determine range.

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Yes, you're right, I've been thinking about one thing and wrote about the other. If ILS has a DME, then it's a separate installation, usually placed at or near the glideslope beacon and working on the ILS frequency (well, not really, but it's the same for the pilot).

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Yes, you're right, I've been thinking about one thing and wrote about the other. If ILS has a DME, then it's a separate installation, usually placed at or near the glideslope beacon and working on the ILS frequency (well, not really, but it's the same for the pilot).

 

Correct. DME channels are paired to the VHF frequencies of VORs and localizers.

 

Note that it is possible to receive VOR guidance from one station and DME distance from another station under certain conditions, so do be sure you can verify the Morse code of both the VOR and the DME. The DME ID makes sense if you are at high altitude and are getting unexpected DME values.

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Hi my friends and sorry for my english

 

in FSX when u want to adjust the instrument for ILS u must have frequency and course but in DCS when u look on the map for the airport ( base ) just u can see the frequency for ILS and there is no number for the course .

 

so how i can find what,s the course and then adjust my course on the course selector indicator ?

 

And the other thing that i,m not sure is...... in fsx u can see the number of the runway from the sky but in DCS I can,t see the number so i,m not sure this is the right run way that i have to use for landing or wrong ?

 

plz help ma and thanks

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You have to look on the map in the mission editor or use one of the maps from the download section. Unfortunately the exact ILS courses are not visible on the F10 map.

 

Runway number can be checked on the map by clicking on the airport icon.

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TACAN/VOR/DME/Fixes/Airways/NDBs are used for navigation. Charts used in IFR and VFR have at least one nav fix in order to help get in landing pattern. So essentially, navaids pass you to the landing. Also, TACAN is used in AAR to home on the tankers in the A-10C. A tactical reason is you want to minimise radio chatter across so the enemy is not aware where you are or friendlies are.

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You have to look on the map in the mission editor or use one of the maps from the download section. Unfortunately the exact ILS courses are not visible on the F10 map.

 

Runway number can be checked on the map by clicking on the airport icon.

first those runway numbers on runway are not accurate enough, second some of those numbers on charts are totally incorrect!!! faced lots of issues using these numbers as course, the ways I usually use are 1-setting the course when the plane is lined up or 2-using ruler (and using those numbers to update the charts) otherwise you're probably gonna be landing right into dirt or ramp:joystick::joystick:.

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Hi my friends and sorry for my english

 

in FSX when u want to adjust the instrument for ILS u must have frequency and course but in DCS when u look on the map for the airport ( base ) just u can see the frequency for ILS and there is no number for the course .

 

so how i can find what,s the course and then adjust my course on the course selector indicator ?

 

And the other thing that i,m not sure is...... in fsx u can see the number of the runway from the sky but in DCS I can,t see the number so i,m not sure this is the right run way that i have to use for landing or wrong ?

 

plz help ma and thanks

 

FLIP for Georgia, Russia, and Nevada that we made in the 476th may help. We didn’t do all the airfields in Georgia just the ones we use the most.

 

http://www.476vfightergroup.com/downloads.php?do=cat&id=44

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And the other thing that i,m not sure is...... in fsx u can see the number of the runway from the sky but in DCS I can,t see the number so i,m not sure this is the right run way that i have to use for landing or wrong ?

 

Not sure whether or not real pilots actually check the numbers on the runway, but as a rule of thumb... let's say you're on final approach runway 27 and your course is between 260 and 280, I'd say you're roughly in the right spot. If your course is anything else, you probably aren't. :music_whistling:

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