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victorlima01

IAN approaches and the Approach Reference Page of the CDU

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Lately I´ve been trying to do some reading regarding Integrared Approach Navigation since I believe this is something that will become quite common in the near future with the multiplication of Rnav approaches with ever decreasing RNPs which modern airlines such as the NGs are capable of satisfying. From my understanding, IAN basically is a pretty clever way of taking all available navigation data that is fed into the FMCs to generate an artificial glideslope which can be coupled to non-precision instrument approaches. In other words, you take an airplane-generated glidepath, marry it to a localizer, vor, ndb or rnav approach and thus end up with an ILS-like approach that makes vertical navigation easier. Ever since I saw that green G/S in the CDU´s APP REF page I knew it had something to do with IAN. I looked it up in the FCOM (vol. 2) and sure enough, according to page 11.43.30: "Glideslope (G/S) [Option – With QFE/QNH selection, alternate destination prediction, and integrated approach navigation] Toggles glideslope on and off for the selected or active approach. When a localizer based approach is selected or active, and an FMC generated glidepath (G/P) is to be flown, glideslope (G/S) must be turned off. " That´s what I don´t get. Seems counter-intuitive. Or maybe I simply haven´t grasped the concept behind IAN yet. But wouldn´t it work the other way around. I mean, if you want to have glidepath to the rwy when you do not have a glideslope available (i.e, flying a LOC app) shouldn´t you activate the G/S on the APP REF page of the CDU? I think I need help either from Ryan or some of our RW counterparts!


Cheers,
Victor M. Lima
 

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See FCOM vol 2.....pages 232/233 !! It is well explained there.
Thank you Jason, this did help. However there still is no explanation for what I mentioned earlier. Guess I'll have to play with it and see what happens.

Cheers,
Victor M. Lima
 

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When a localizer based approach is selected or active, and an FMC generated glidepath (G/P) is to be flown, glideslope (G/S) must be turned off. " That´s what I don´t get. Seems counter-intuitive. Or maybe I simply haven´t grasped the concept behind IAN yet. But wouldn´t it work the other way around. I mean, if you want to have glidepath to the rwy when you do not have a glideslope available (i.e, flying a LOC app) shouldn´t you activate the G/S on the APP REF page of the CDU?
I think it's quite logical. If you fly a localizer approach you are already provided with a radio based glideslope that the aircraft can fly. The calculated glideslope from the FMC is superfluous in such a case and might even be in conflict with the localizer glideslope.

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You are selecting the radio glideslope on/off. Not sure about the real aircraft (which actually has descent angles programmed in the database), but this also displays the final approach descent angle on the legs page (over the runway fix). You should make sure that this is OFF for IAN and VNAV approaches.


David Zhong

 

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If you fly a localizer approach you are already provided with a radio based glideslope that the aircraft can fly.
Huh? Why? If it's a true LOC app you certainly don't have a physical G/S, right? sig.gif

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You are selecting the radio glideslope on/off. Not sure about the real aircraft (which actually has descent angles programmed in the database), but this also displays the final approach descent angle on the legs page (over the runway fix). You should make sure that this is OFF for IAN and VNAV approaches.
Oh I see now. If it's the radio glideslope you're selectiong off than it makes oerfect sense. I thought it was in reference to the FMC computed glideslope (which by the way is glidepath, not slope, and I should've thought of that). Do you guys know about a good tutorial or read out there that teaches about IAN approaches and Rnav approaches in the NG? I mean other than and deeper than the FCTM. Thanks
Huh? Why? If it's a true LOC app you certainly don't have a physical G/S, right? sig.gif
Right, I think he meant a full ILS approach with localizer and glideslope radio beams. There's no physical g/s in loc approaches

Cheers,
Victor M. Lima
 

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A localiser approach is any one where you do not use a radio glideslope for guidance. Almost all ILS approach charts have "ILS or LOC RWY XX" as the title to reflect the fact that a localiser approach may be conducted with the equipment.


David Zhong

 

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Huh, alright then. This got me really confused now as well, so thanks for bringing it up to confuse me. LOL.gif Tests reveal something unexpected (for me):There seems to be a difference between "true" LOC approaches and ILS approaches that can be flown as a LOC. Observations:"True" LOC runway (NO physical glideslope): Selecting G/S ON will make G/P possible for IAN. G/S OFF can be flown with VOR/LOC/VNAV as usual. Nothing spectacular here, just like any good old NPA. "Full ILS" runway, but flying a LOC app (so it HAS a physical glideslope): G/S ON will fly the ILS with VOR/LOC/G/S (go figure). G/S OFF however, will enable IAN capability and VOR/LOC/G/P (contrary to everything else and all other NPAs!). Anyone who has time to confirm is more than welcome to do so. sig.gif

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So, if I understand what you all have concluded, the G/S ON or OFF selection is ONLY relevant in the case of a full ILS approach being flown without using the published GS either by choice or because it is out of commission. With all non-precision approaches this should always be selected to OFF then so that FMC will generate a flight path. Is that correct? The difference then between flying the non-precision as a Lnav/Vnav and an IAN would be whether or not the APP is used to intecept the inbound course. If that is correct, then I have experienced some unexplained anomalies. First, off, the GP info on the legs page is only for the segment from the last fix to the runway threshold whereas the FCOM seems to imply that GP info must be generated for the full approach or at least from the FAF inbound to qualify for an IAN. I have tried various combinations and sometimes "fac" and "gp" are displayed on the annunciator panel and other times I only get "Lnav" and "Vnav" and I can't seem to determine what causes the difference. The Fcom states that a nav frequency must be active on at least one radio in order to allow an IAN, but the RTM NGX version I am using will allow an IAN even on a visual approach ( by presetting an inbound fix prior to the runway) with no nav radio frequency selected. I then get either "fac" or "fmc" as roll mode and "gp" as pitch mode on the annunciator. And I can then fly a full IAN approach using the PFD bars for GS and the ND display for "localizer"! I think I have always been setting the GS to ON for these. I agree with Victor. We need to find a more detailed step-by-step or tutorial to shed positive light on this exciting new feature.


Craig Williams

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With all non-precision approaches this should always be selected to OFF then so that FMC will generate a flight path. Is that correct?
No, I think quite the opposite is. Select G/S to ON in order to get IAN capability (FMC generated G/P), and FAC/G/P indications when selecting APP. Otherwise you'll be using LNAV/VNAV (without G/S selected, that is).
The difference then between flying the non-precision as a Lnav/Vnav and an IAN would be whether or not the APP is used to intecept the inbound course. If that is correct, then I have experienced some unexplained anomalies. First, off, the GP info on the legs page is only for the segment from the last fix to the runway threshold whereas the FCOM seems to imply that GP info must be generated for the full approach or at least from the FAF inbound to qualify for an IAN. I have tried various combinations and sometimes "fac" and "gp" are displayed on the annunciator panel and other times I only get "Lnav" and "Vnav" and I can't seem to determine what causes the difference.
Well yes, G/S deselected means no IAN, means you'll be using LNAV/VNAV. Set G/S to ON however, you can still use LNAV/VNAV if you wish, but otherwise you could hit APP and enter FAC/G/P modes.
The Fcom states that a nav frequency must be active on at least one radio in order to allow an IAN, but the RTM NGX version I am using will allow an IAN even on a visual approach ( by presetting an inbund fix prior to the runway) with no nav radio frequency selected. I then get either "fac" or "fmc" as roll mode and "gp" as pitch mode on the annunciator. And I can then fly a full IAN approach using the PFD bars for GS and the ND display for "localizer"! I think I have always been setting the GS to ON for these.
I just tried twice but IAN on a visual certainly doesn't work for me. In case you mean visual by selecting only a runway on the DEP/ARR page (no approach), then add a runway extension. Doesn't work for me. I can select G/S, but neither do I get any indications nor would VOR/LOC or APP arm let alone engage in FAC or G/P. sig.gif

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Huh? Why? If it's a true LOC app you certainly don't have a physical G/S, right?
Sorry, misread the question! rolleyes.gif

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Thanks, actually I just posted a follow up question over there. Noticed some weird things happen with LOC approaches recently. sig.gif

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Did you notice you can also fly an ILS (!) using IAN? Just retune your NAV radio to some wrong frequency and hitting APP will happily arm FAC/G/P. So IAN seems to be some sort of fallback mode there. Not sure if the real thing would allow that. Kinda weird methinks. sig.gif

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