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ILS Flight Director Influenced by Course Selector


Joni
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[EDIT] You put in a course that's published on the approach plate and your aircraft calculates the CDI deviation based on your course input. Since magvar changes, you may see published approach plate courses change over time.

 

First thing they teach us in IFR school: published courses are for situational awareness only.

 

 

Think of an ILS like it's just a NAVAID like a VOR/TACAN but confined to a precise cone - if you change the course and center the CDI, you'll change your ground track radial just like you would on a VOR/TACAN.

 

No, ILS is exactly NOT "just like" a NAVAID, specially VORs. The computer or instrument itself doesnt recognize where you want to fly to, it just knows where the BEAM is!

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One other thing to help you understand the system. When you change the selector knob the HSI deviation DOESNT change for the exact same reasons ive been presenting here. Why would the director change? Pls explain :)

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It looks like there are two different discussion going on here, hence the diverging opnions.

- Is the course value needed for an accurate LOC capture? Yes - but maybe not on all A/C types, on my side I can only guarantee it is need for airliners.

- Is the HSI course value used for that? Probably not, that's a different instrument - On airliners again, the only places you can tune that course is through the radio management panel (in manual mode) or through the FMS (in managed mode).

 

So, I'm not saying Piston85 is wrong about saying HSI course selector should not affect ILS' autopilot, I'm just saying that you can't justify this by saying no ILS autopilot ever uses a course value, this is something that depends on the A/C.

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There is no value whatsoever in the airplane voluntarily deviating from the captured localizer in order to satisfy some erroneous inbound course setting. I can't say for certain that every aircraft and avionics manufacturer feels the same way, so it's conceivable that maybe an A320 will wonder off...but the A-10 doesn't.

I saw that happen (veering off due to incorrect course setting, then correcting back to compensate for the deviation it generated), I think it was on a A320 but not sure :)

Not real airplane, a simulator, but using a real autopilot software (I think it was before capture, but it's been a while, I don't remember the test conditions).


Edited by PiedDroit
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built on a SINGLE beam that the reciever (aircraft) gets. Therefore it is not affected by course selector since it is acquiring ONE signal

 

One doesn't determine the other. VOR is a single antenna receiving a single signal as well. Rather it is two signals mixed but so is localizer. There's nothing preventing a design that has as input the lateral error, heading, and manual course and spit out a flight director needle movement. A-10 doesn't and you're totally right about that. I don't have real experience with flight directors relating to ILS signals. Some (most? all?) designs figure things out from trend-history data or are there (were there) designs that required manual data input for course? I don't know.

 

The localizer and glide path(-slope for the non-ICAO folks) are two separate systems

 

In total there are 4 distinct signals, two for localizer and two for glide. If you want to define a "beam" as a mixture of 2 or 4 signals then that's up to you.

 

CRS knob means that VOR must be possible in the real AC right

 

TACAN and INS navigation use the CRS knob. No VOR A-10 capability.

 

Name one system that uses course selection please. After 15 years ive never seen one.

 

Closest thing I know of is F-16 ILS HUD cues has a caret mark on the heading HUD tape for wind-corrected heading. This requires manual entry of the inbound course (not via crs knob, a text entry into a menu) to direct correctly. There are other ILS steering cues on the HUD (I think) function irrespective of input course as the A-10 does.

 

You put in a course that's published on the approach plate and your aircraft calculates the CDI deviation based on your course input.

 

For INS and TACAN/VOR yes, but not for ILS. CDI deflection when hooked up to ILS signal deflects based on relative mix of the two signal modulations. Turning the CRS knob on a traditional ILS instrument only orients the instrument visually. The CDI deflection won't depend on a selected course of this I'm 101% certain.

 

The electronic beams point you in the direction by comparing deviation

 

Position data is from the deviation of the two signal modulations but FD must display different commands even for the same instantaneous position. For FD to function only with localizer data it must also know a history of localizer data. Instantaneously it cannot tell apart "established center" and "transiting center" for example.

 

On center + history of changing to the right = bank left

On center + history of remaining on center = zero bank

On center + history of changing to the left = bank right

 

ILS is certainly a radio navigation aid. But certainly all radio navigation aids do not respond to a course selection equally (VOR, A-N, ADF, ILS, Lorenz, PRMG, MLS, etc.).

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Apparently IRL 9/10 VORs are broken and ATC assumes everyone operates on GPS nowadays.

 

In my experience, the inop rate (of the VORs that are part of the protected set) is less than 5%. Downtime typically lasts less than a week when they fail.

 

ILS will give you deviation based on what course you put in because magnetic variation changes. ILS is modeled correctly in the A10: you must input the correct CRS for ILS to be accurate.

 

Not true. A localizer is fixed to the ground, transmits a beam with a fixed orientation. Your navigation antenna detects the relative strength of the left and right signals and uses that to determine your position left or right of the beam center. That relative position is displayed on the CDI.

 

The heading knob on a CDI is only used when you're using a VOR for navigation, since a VOR transmits timed pulses in all directions (360 different radials) and you have to determine which one you want to show as centered.

 

Now the problem is that there are many different precision/non-precision and types of ILS so its kind of hard to define ILS in general since they vary.

 

I would say there are many types of approaches, but only one ILS.

 

[EDIT] Direct from him "I've got a few hours in both /G aircraft' date=' and /A single-engine jet and I'm instrument rated. You put in a course that's published on the approach plate and your aircraft calculates the CDI deviation based on your course input. Since magvar changes, you may see published approach plate courses change over time. Think of an ILS like it's just a NAVAID like a VOR/TACAN but confined to a precise cone - if you change the course and center the CDI, you'll change your ground track radial just like you would on a VOR/TACAN. This is very important for approaches such as LDA - Localizer-type Directional Aid. An LDA approach is a non-precision approach that uses the localizer beam of an ILS to offset the final approach course to maintain obstruction (or noise abatement) clearance."[/quote']

 

Your brother is mistaken. LDA, LOC and ILS approaches all use the same localizer hardware. An LDA simply has the hardware at an angle more than 3° different than the runway heading. Your navigation radio knows its an ILS (localizers and VORs don't share frequencies) so it displays finer-resolution CDI guidance, as long as you're within the 30 degree cone. (A localizer beam width is about 30 degrees within 10 miles, however, that's where the NAV flag disappears. To actually see the CDI needle move, you need to be within 2.5° degrees of centerline.)

 

None of them are affected by the CDI heading knob.

 

This is actually a useful property when a waypoint on an ILS approach is identified by the cross radial of a VOR, because you fly the ILS and periodically swap to your alternate frequency on your nav radio to confirm your current VOR radial. This swap and confirm only takes 2-3 seconds, so it can be done while flying an ILS by hand if you don't have a second CDI.

 

--gos

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In my experience, the inop rate (of the VORs that are part of the protected set) is less than 5%. Downtime typically lasts less than a week when they fail.

 

 

 

Not true. A localizer is fixed to the ground, transmits a beam with a fixed orientation. Your navigation antenna detects the relative strength of the left and right signals and uses that to determine your position left or right of the beam center. That relative position is displayed on the CDI.

 

The heading knob on a CDI is only used when you're using a VOR for navigation, since a VOR transmits timed pulses in all directions (360 different radials) and you have to determine which one you want to show as centered.

 

 

 

I would say there are many types of approaches, but only one ILS.

 

 

 

Your brother is mistaken. LDA, LOC and ILS approaches all use the same localizer hardware. An LDA simply has the hardware at an angle more than 3° different than the runway heading. Your navigation radio knows its an ILS (localizers and VORs don't share frequencies) so it displays finer-resolution CDI guidance, as long as you're within the 30 degree cone. (A localizer beam width is about 30 degrees within 10 miles, however, that's where the NAV flag disappears. To actually see the CDI needle move, you need to be within 2.5° degrees of centerline.)

 

None of them are affected by the CDI heading knob.

 

This is actually a useful property when a waypoint on an ILS approach is identified by the cross radial of a VOR, because you fly the ILS and periodically swap to your alternate frequency on your nav radio to confirm your current VOR radial. This swap and confirm only takes 2-3 seconds, so it can be done while flying an ILS by hand if you don't have a second CDI.

 

--gos

 

Gospadin,

 

You being on the testers team, have you brought up ILS being affected by the CRS knob?

 

 

Happy Simming,

Monnie

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You being on the testers team, have you brought up ILS being affected by the CRS knob?

 

No, I only have access to NS430-related stuff for testing.

 

I'll PM someone who does, though.

 

FWIW, the UH-1H CDI and HSI hardware works as I am used to in real life, if people want to compare behaviors.

 

--gos

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No, I only have access to NS430-related stuff for testing.

 

I'll PM someone who does, though.

 

FWIW, the UH-1H CDI and HSI hardware works as I am used to in real life, if people want to compare behaviors.

 

--gos

 

Gospadin,

 

Thank you for the quick response and forwarding this to the appropriate tester contact. Please suggest the contact post in this thread any information about/confirmation/updates and if any thing is needed to expedite this issue.

 

 

Happy Simming,

Monnie

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  • 2 weeks later...

Gospadin,

 

 

Any update on if you brought this to the attention of the appropriate tester?

Has that person initiated a internal report?

Do we need to give any additional information to expedite this?

 

 

Happy Simming,

Monnie

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So who has shared A-10C specific documentation to say it is 100% wrong? All I see is people saying it works a different way in aircraft x, y, and z.

 

ED isn’t going to change anything unless they have specific A-10C documentation.

 

Not saying y’all are wrong but I have been digging through A-10 tech orders and can’t find anything one way or another.

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So who has shared A-10C specific documentation to say it is 100% wrong? All I see is people saying it works a different way in aircraft x, y, and z.

 

ED isn’t going to change anything unless they have specific A-10C documentation.

 

Not saying y’all are wrong but I have been digging through A-10 tech orders and can’t find anything one way or another.

 

Snoopy,

 

Would you be able to just ask a hog driver if the course knob ( say set to 90° off) affects / effects the ILS?

 

Would that information if answered be able to be forwarded?

 

 

Happy Simming,

Monnie

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Snoopy,

 

Would you be able to just ask a hog driver if the course knob ( say set to 90° off) affects / effects the ILS?

 

Would that information if answered be able to be forwarded?

 

Happy Simming,

Monnie

 

I’m reading through the ILS portion of the C-2-1-1 now and post what i find later this evening.

 

But ED won’t change things based on interviews either.

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Snoopy,

 

Thank you so much for taking the time to read through it. You are a great help to the community.:thumbup:

 

I would think a real hog driver, a USAF / Marines Commissioned Officer with flight hours in a A-10C would be a SME to say the least.

 

 

 

Happy Simming,

Monnie


Edited by MonnieRock

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Who are you referring to?

 

A pilot you come in contact with during duty hours.

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A pilot you come in contact with during duty hours.

 

:huh:....Marines don't fly A-10s :doh:

 

I can't find anything specific in the 2-1-1 but in another real world training document (and I can't share with anyone or ED) part of the ILS approach verbage states that you must dial in the localizer course using the HSI Course set know and select the ILS button the NMSP.

 

I take this to mean it is modeled correctly in DCS A-10C.

A-10C LIDS Check.

L(ocalizer station); select ILS on NMSP and ensure correct frequency on ILS control panel, tune, identify, and monitor

I(inbound course); Set course using HSI course knob

D(ME); set for localizer

S(low); to final approach speed


Edited by Snoopy
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Shows you what I know :doh:

 

I was just an Army guy :music_whistling:

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  • 4 months later...

Well IMHO, there is difference between the HSI course deviation bars and ADI flight director bars.

 

The deviation bars works only with the ILS signal. But IMO the flight director can not operate properly without knowing the runway direction. Because when there is the crosswind and the system does not know the runway course, it will navigate you with the deviation caused by crosswind. But when the system knows the runway course, it can compensate this deviation caused by wind.

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I don't uderstand then. Because this is how it in DCS works for years. You just set the runway course into HSI and the flight director bars on ADI are compensating the deviation caused by the crosswind. Just like I've wrote. That makes landings much easier. And that is how flight director should work.


Edited by AJaromir
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Well IMHO, there is difference between the HSI course deviation bars and ADI flight director bars.

 

The deviation bars works only with the ILS signal. But IMO the flight director can not operate properly without knowing the runway direction. Because when there is the crosswind and the system does not know the runway course, it will navigate you with the deviation caused by crosswind. But when the system knows the runway course, it can compensate this deviation caused by wind.

 

Piston85 is right. The flight director can (and does) operate without knowing the localizer course. I had the same mistake of thought originally too, that command output cannot function without comparing heading or track to some pilot-input course info. Localizer signal mix is not enough info to reach a solution and display command output. The error is thinking that this is the only info it has.

 

The flight director knows more than just the current localizer signal; it also knows rate. Position is not enough but position and rate is enough info to calculate bank to command without knowing the course of the localizer.

 

The proof is right in Figure FO-7, row HSI COURSE SET Control, column ILS; it's a big empty square. The CRS knob has no function for ILS.

 

ADI steering bars are initially out of view. Bank bar unstows when localizer is captured which is within 2.6 dots CDI displacement. Pitch bar unstows when glide slope is captured of GSI 0.5 dot from center initially showing -2 pitch command (presumably until GSI crosses centered indication) and then normal intercept command. Bank command is limited 30 degrees pre-GS-capture and 15 degrees post-GS-capture.

 

Certain EGI failures may cause ADI bank steering errors with STR PT or ANCHR but such is not the case for ILS because the ILS operates independently of EGI (it's not comparing the CRS knob setting to anything regarding EGI heading or track). Similarly TACAN, TISL, and FM homing are unaffected since they too do not rely on EGI.

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