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ILS FPM


Joni
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Hi!

 

I noticed that the closed box during ILS approaches behaves like a localizer/glideslope indicator rather than a director as stated in the manual. Therefore placing the FPM inside the box makes no sense as the box will always be deviated as long as the localizer is; same for the vertical component (GS).

 

Does anyone know if this is a bug or a missconception of the real system?

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Example here although it is the obvious way to behave like in every plane.

 

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Everything looks good,

 

The manual clearly states that the box shows glideslope and course deviation.

 

It indeed says that for a perfect approach you have to place the FPM inside the box, but you have to read this as "you have to maneuver so the FPM is inside the box".

The box is not a flight director (also no flight director would work by using the FPM as pointer anyway, it would be a fixed point in the HUD).

 

1. ILS Guide

Visible only when both localizer and glideslope have been captured. It moves in

relation to the FPM showing both glideslope and course deviation. To maintain a

perfect approach, you have to place the FPM inside the box.

 

If the deviation from either glideslope or course is too large, a flashing triangle (not

shown) will appear indicating that a course/elevation change is required.

 

Therefore placing the FPM inside the box makes no sense as the box will always be deviated as long as the localizer is; same for the vertical component (GS).

Actually the box is displayed relatively to the FPM, so when the FPM is in the box, deviation is exactly zero, so you're on flight path.


Edited by PiedDroit
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Ive been flying (real life career + air force) for more than 15 years and this is the first time I hear something like this :)

 

Have you ever seen a plane that behaves like you say? It goes against the conception of a HUD.

 

THanks anyway for your kind reply.

What I mean is that you will not have the FPM used as a pointer for a fixed point in the HUD.

You will have either:

- a fixed point in the HUD matched against HUD-centric cues, or

- the FPM matched against FPM-centric cues.

Not a mix of both.

 

Your mileage may vary I guess (mine in that case). I also saw my share of flight directors, HUDs and stuff alike (I work with avionics, not for as long as you did though), never saw anything that requires you to put the FPM into something that is not relative to the FPM.

 

Anyway, for the ILS we're talking about, what I'm saying is that the box is FPM-related, so asking to put the FPM in the box to obtain zero deviation is normal.


Edited by PiedDroit
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What I mean is that you will not have the FPM used as a pointer for a fixed point in the HUD.

You will have either:

- a fixed point in the HUD matched against HUD-centric cues, or

- the FPM matched against FPM-centric cues.

Not a mix of both.

 

Your mileage may vary I guess (mine in that case). I also saw my share of flight directors, HUDs and stuff alike (I work with avionics, not for as long as you did though), never saw anything that requires you to put the FPM into something that is not relative to the FPM.

 

Anyway, for the ILS we're talking about, what I'm saying is that the box is FPM-related, so asking to put the FPM in the box to obtain zero deviation is normal.

 

Sorry, I just realized that Razbam already agreed this was a bug https://forums.eagle.ru/showthread.php?t=172120&page=3

 

There is a video of the same system and how it is supposed to behave (already posted that video in the first post)

 

 

:)

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The video you posted above is a good example of what I'm talinkg about, in the attached picture I just highlighted some elements, in red some that are attached to the HUD frame, in blue some that are mapped to the actual flight vector.

But I'm just stating the obvious anyway.

 

I never said it's not fpm related, actually it should be. If the box is in relation to FPM then it must act as a director (otherwise we would be talking about apples and oranges). If the box is not FPM related then it could act as loc/gs deviaton indicators; Period, there is not really much to discuss in that regard.

This is where there is a confusion I think.

"If the box is in relation to FPM then it must act as a director" - why must?

Flight director and deviation indicator are two different things, the flight director show deviation between flight path computed by the flight guidance versus actual flight path, where deviation is a raw value that shows the angular difference between the localizer beam (and g/s) versus your current position.

 

So having the box, let's say on the right of the FPM could very well mean two things: in case of a flight director implementation, it would be a command from the flight guidance to go right in order to catch the computed flight path.

In case of a deviation indicator, it would simply tell you that the localizer beam is on the right.

 

If the FPM is on top of the box, it just means deviation is 0. lets says you are on a 90° course in relation with the runway, and your position is right on the runway axis (runway in your 3/9 O'clock).

In that case the deviation indicator will show zero (FPM on top of the box), but a flight guidance system would put the flight director to the left or right of its anchor because obviously you'd need to do a turn to catch the loc beam.

 

Sorry, I just realized that Razbam already agreed this was a bug https://forums.eagle.ru/showthread.php?t=172120&page=3

 

There is a video of the same system and how it is supposed to behave (already posted that video in the first post)

 

 

:)

 

If the real manual says it's a deviation from the LOC beam, then it is, it is not a flight director and you can't use another aircraft's footage to prove your point...

If RAZBAM acknowledged the above as bug, then I think it's a mistake (unless they have data that we don't have).

The only thing is that the manual is not 100% clear, I think this has been discussed in another thread, I'll to dig a bit to find it.

HUD2.thumb.png.153040d5ce46130255cadcf77a9ae037.png


Edited by PiedDroit
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Thanks, hope it gets corrected soon.

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Yet I fully understand the topic, take some time to think about it.

There is no conclusive data that goes one way or another (sorry but an A319 HUD footage doesn't prove anything), I'd love to see something more solid than that.


Edited by PiedDroit
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I feel sorry that PiedDroit tried to help you with this topic as you don't seem to value his time and knowledge.

 

Can we now keep the thread on topic that is the PFM behavior with the HUD in ILS mode ?

 

It would be bad to make the mods close a legit bug report for off-topic (again) :).


Edited by myHelljumper

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Ok, I deleted my posts in order to keep the discussion on track.

 

What other proof is needed? Im not sure if it was clear or something else is on the table.

 

We have Razbam acknowledge, a video of the same system, a word of a pilot, the nature of an FPM during ILS.

 

If the manual (written by Razbam not the real plane) says to actively put the fpm inside the box they are referring to FD, otherwise it would say put THE BOX in the center of the HUD and then keep the FPM inside.

 

Maybe i came too harsh on people who are not pilots, but the error exists.

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Good, very good, I prefer tackling problems rather than people :)

 

If RAZBAM have a SME that confirmed it, it's OK, but otherwise we have to rely on the manual.

I have attached the two pages on ILS I have from the real manual.

 

This is where I think the confusion is coming:

 

If the manual (written by Razbam not the real plane) says to actively put the fpm inside the box they are referring to FD, otherwise it would say put THE BOX in the center of the HUD and then keep the FPM inside.

 

You seem to be sure that if the indicator is relative to the FPM, then it is a flight director and if the box was a deviation indicator, it should be put in the center of the HUD, but I disagree here.

A deviation indicator is not necessarily to be put in the center of the HUD. It might be true for an Airbus, but we're talking about a different beast here. The deviation indicator could very well be tied to the FPM. There is no other indicator on the Mirage's HUD (the Airbus has the vertical deviation on the right of the HUD).

At the same time, for example, a flight director is not necessarily tied to the FPM. On an Airbus' primary flight display (not HUD), the fligh director is a green cross that you need to put in the center of the display, it's not tied to the FPM.

 

The real manual says:

"Put the aicraft model in the guiding window". That kind of sentence could apply to both a flight director (commands from flight guidance computer) or a deviation indicator (raw deviations from ILS receiver).

If you maintain the FPM in the box, then you're on path, it works for both.

 

There is also a little triangle on the picture that says "Excessive LOC deviation (flashing)". That kind of terminology is associated to a deviation indicator, not a flight director.

 

So, if the box is a deviation indicator and tied to the FPM, there is no need to put it in the center of the HUD. If the box is on the right of the FPM, then it means that you are to the left of the path, vice versa, same in vertical.

That works for both a flight director and a deviation indicator.

 

The proof that is needed is a SME that confirms either possibility.

What I'm saying is that the instruction to put the FPM in the box is not enough to decide this is flight director. Especially when this box can have a little triangle that says "Excessive LOC deviation".

M2000CILS1.PNG.ca32acfe2c0d184d5db95ba900731dc5.PNG

M2000CILS2.PNG.d34dd93a28ec60ee381f01f996b6bded.PNG


Edited by PiedDroit
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There is also a little triangle on the picture that says "Excessive LOC deviation (flashing)". That kind of terminology is associated to a deviation indicator, not a flight director.

 

That above is the one thing you're righr. Maybe that confirms everything about me being wrong.

 

What does the real manual say aboout the indications in the ADI? I find those to hardly be deviations, all yellow needles are directors for international convention.

 

Can you find that? I could not get to the real manual online, dont know where else to look.

 

 

Sorry for before.

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That above is the one thing you're righr. Maybe that confirms everything about me being wrong.

 

What does the real manual say aboout the indications in the ADI? I find those to hardly be deviations, all yellow needles are directors for international convention.

 

Can you find that? I could not get to the real manual online, dont know where else to look.

 

 

Sorry for before.

 

No problem, I'm a patient person and can deal with that, I apologize for my reaction.

 

The manual has no details about the ILS, the only thing are these pictures.

 

The fact that there is an autopilot that can follow a glislope would be a good argument to say that the box is fligth director, because after all, why not display the flight guidance commands when you have them? It's much better than a raw deviation.

 

The data from the manual is just too scarce to conclude anything.

I have been advocating for an ILS deviation indicator because of the way the drawing is done and the terms presented in the manual, but it is very thin. I'd love to have more data from a SME.

 

I don't have anything more to add here, next move is RAZBAM's choice, I only wanted to expose that because I had the feeling that this HUD footage from an Airbus had been taken too lightly.

I deal with avionics systems every day and even with a same type of aircraft you can have a lot of tiny differences to be looked at with a magnifying glass.

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Correct, almost all AP ILS capable planes display the commands, that's why I asked about the ADI, i find it very strange.

 

 

Thank you.

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I tried to re-read the manual more carefully and I found this:

 

"In the HUD, the presence of the star representing the commanded slope, indicates the pilot that the autopilot is connected".

Could that indicate that the flight director is the star?

 

The other picture I have attached is for the visual approach, the text in the box says that autopilot is connected, and we can see the star in the HUD, and that the FPM should be put on the star.

 

In comparison, the 2 pictures in the other post I made don't say that the autopilot is connected.

 

The manual I have (m2000c.pdf found on the net) is a scanned document with no OCR, so it makes looking for stuff a bit difficult.

The paragraph on the ADI ("spherical indicator") only state that it displays the ILS cues (Marker - LOC - Glide).

 

My best guess woud be:

* -> flight director

box -> deviation indicator

M2000CILS3.PNG.20ee8d29327c1f70c17fd9f78c25d4e8.PNG

M2000CILS4.PNG.e7051548095c8cfab8b3e398cb32a216.PNG


Edited by PiedDroit
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The star is actually the point in which you want the FPM to fly the plane to. Its controlled by the trim hat in hotas.

 

The director should indicate the pilot what to do during manual flight, not during automatic one. The star dissapears after disconnecting the ap.

 

I agree we need some mirage pilot to tell us how it was done ;)

 

Jeez I would really like to read something about the ADI!

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(maybe seeing how the approach autopilot flies the ILS slope might be insightful as to how to do it manually? ...unless it's not accurate, either)

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The data from the manual is just too scarce to conclude anything.

I have been advocating for an ILS deviation indicator because of the way the drawing is done and the terms presented in the manual, but it is very thin. I'd love to have more data from a SME.

 

To me, this is wrong idea, but we've already discussed it in another topic in length. To show deviation you need some sort of stable reference point, that shows you how much you've deviated from the center path. FPM is not a reference point, as it floats around constantly and there is no other indicator that can be used on the HUD. Hence, the deviation information displayed to the pilot by the box as we currently have in the sim is meaningless and counter-intuitive. Sometimes you have to steer the other way from where the box is displaced.

 

I don't know about any HUD system that works this way in real life, either American or European. They all show guiding information (flight director) on the HUD and instruct the pilot to keep the FPM superimposed over guiding cue all the time.

 

I don't understand French and its nuances, but to me "FENETRE DE GUIDANCE" sounds much more like a flight director would be labeled. ("guiding box" or something).


Edited by some1

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I don't understand French and its nuances, but to me "FENETRE DE GUIDANCE" sounds much more like a flight director would be labeled. ("guiding box" or something).

 

I agree, to me "fenêtre de guidage" would mean a flight director rather than a deviation indicator. Also the phrase "mettre la maquette avion dans la fenêtre de guidage" doesn't sound like a deviation indicator. It's then not just as simple as putting the FPM into the box, but rather navigating the airplane to align with the localizer and glideslope.

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I agree, to me "fenêtre de guidage" would mean a flight director rather than a deviation indicator. Also the phrase "mettre la maquette avion dans la fenêtre de guidage" doesn't sound like a deviation indicator. It's then not just as simple as putting the FPM into the box, but rather navigating the airplane to align with the localizer and glideslope.

 

This and the above make sense to me.

 

Plus I heard (grain of salt here, might not be reliable info) that pilots would rather use the ADI than the HUD for ILS approach, if the box was a deviation indicator it won't make a lot of sense as the info would be "almost" the same on the HUD and the ADI. OTOH if the box was a flight director the pilots might not like the way it commanded their approach and/or not find the info they wanted.

 

It was said previously but the landing autopilot would just have to follow the flight director.

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I think a bug report is almost useless now with Razbam. Too much effort on the Harrier and the Mirage's FM update.

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I think that if Dassault made the box a flight director then maybe DCS Mirage should also have it that way.

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Also, I just realized that the box DOES behaves like flight director on the GS part!! Its telling you exactly what attitude you should have to follow a perfect glide path.

 

So... ideas?

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