LOC, APPR and descent altitudes.

[Liam123 1]

1. When exactly do I arm the LOC button? Can I activate it too early or can I just press it when I'm descending so I know it'll capture it eventually?

 

2. If I capture the localizer, how long after do I activate the APPR switch? Is it once the lower diamond is in the middle, meaning the plane is on line with the runway?

 

3. After following a flight plan on my MCDU, when I get to the top of descent, how do I know which altitude to descend to so I'm at a good altitude to capture the localiser? 

 

Appreciate the help! I've made 4 ILS landings and I feel confident in what I'm doing up until the descent, at which point it becomes more or a guessing game and hoping for the best, rather than actually knowing what I'm doing. 

[pgreenwo 117]

Hi Liam

 

Well worth taking the time to do the training flights. You learn the system inside out in a couple of hours.

 

Also some brilliant vids on the forum here

 

 

[skelsey 103]

Hi Liam,

11 hours ago, Liam123 said:

1. When exactly do I arm the LOC button? Can I activate it too early or can I just press it when I'm descending so I know it'll capture it eventually?

You should arm LOC once you are on a closing heading to the localiser. The localiser in the sim is very reliable, but in real life there are lots of different radio propagation effects that can lead to "false" localiser and glideslope beams: therefore it is best to not to arm the mode until you are a) on a closing heading and b) have been cleared to intercept the localiser by ATC, if applicable.

 

11 hours ago, Liam123 said:

 

2. If I capture the localizer, how long after do I activate the APPR switch? Is it once the lower diamond is in the middle, meaning the plane is on line with the runway?

Once you are established on the localiser (i.e. the localiser diamond is centred, or very nearly so), you can arm APPR. You are quite correct in waiting for localiser capture prior to arming APPR: the glidepath is only certified to be obstacle and terrain-safe within a quite narrow corridor either side of the localiser, and therefore you really shouldn't have the aeroplane in GS mode before you are established on the localiser.

 

There are a couple of ATC provisos to arming APPR (and thus GS mode): you must have been cleared for the approach, as opposed to just localiser capture -- "cleared for the ILS"/"cleared for the approach" implies clearance to establish on both the localiser and the glideslope, whereas "report localiser established" implies that you can capture the localiser but must wait for further clearance before descending below your cleared altitude -- in some places this is important for separation against other traffic (landing westerly at Heathrow, for instance, London City departures route underneath the approach path: therefore the controller needs to guarantee that you're not going to start descending until you are clear of that traffic). In this case you will be told "descend with the glide", at which point you can arm APPR. (Hint: if you've not been cleared for the approach or to descend with the glide and you are localiser established with the glideslope needle starting to move down, it's worth a nudge to the controller who has more than likely simply forgotten, rather than waiting until you get too high!).

 

11 hours ago, Liam123 said:

3. After following a flight plan on my MCDU, when I get to the top of descent, how do I know which altitude to descend to so I'm at a good altitude to capture the localiser? 

This will depend on where you are in the world -- terrain (especially) and obstacles will affect the altitude to which you can descend and whereabouts you can descend. The only reliable way of making sure you don't fly in to a mountain is to check the charts and follow the altitudes published on them (if you have selected a STAR and approach in the MCDU, the relevant profile should be loaded in the form of altitude constraints, but this should always be checked against the chart as database coding errors can and do happen). 

 

Having said that, broadly speaking 2500-3000ft above airfield elevation, 10NM out is generally a good starting point if terrain/obstacles are not a factor. The standard glidepath is three degrees -- this means for each nautical mile horizontally across the ground you descend (about) 300ft (this is also a good crosscheck when you are established on the ILS to make sure that you are on the correct profile and have not captured a false glideslope lobe etc). Therefore, 1NM out you should be at around 300ft above the runway elevation; 2NM out 600ft; 3NM 900ft; 10NM out 3000ft, 20NM out 6000ft and so on.

[Liam123 1]

1 hour ago, skelsey said:

Hi Liam,

You should arm LOC once you are on a closing heading to the localiser. The localiser in the sim is very reliable, but in real life there are lots of different radio propagation effects that can lead to "false" localiser and glideslope beams: therefore it is best to not to arm the mode until you are a) on a closing heading and b) have been cleared to intercept the localiser by ATC, if applicable.

 

How do I know I'm closing in on the localiser? Is there something on the navigation display which shows me where about the localiser is? I can see my next waypoint fine as it's indicated by the green line, but it'd be great if I could see the localiser too. If there is, I will just arm the LOC button once my plane is facing the localiser.

 

1 hour ago, skelsey said:

Having said that, broadly speaking 2500-3000ft above airfield elevation, 10NM out is generally a good starting point if terrain/obstacles are not a factor. The standard glidepath is three degrees -- this means for each nautical mile horizontally across the ground you descend (about) 300ft (this is also a good crosscheck when you are established on the ILS to make sure that you are on the correct profile and have not captured a false glideslope lobe etc). Therefore, 1NM out you should be at around 300ft above the runway elevation; 2NM out 600ft; 3NM 900ft; 10NM out 3000ft, 20NM out 6000ft and so on.

 

On the MCDU, there are waypoints and just to the right, altitudes corresponding with each waypoint. On the last few waypoints there's a purple star with something like FL050 etc. I believe this is the 'platform altitude'. Are these altitudes the one I'm supposed to descend to?

 

Here's a tutorial I was watching. At 35:25 he goes down to the MCDU and finds the 'platform altitude of the ILS'. There was two altitudes with purple stars next to them - 4000 and 2340. He didn't say how he knew it was 4000 feet. How can I determine the altitude for each airport?

 

https://youtu.be/XsDnkynT-Rc?t=2126

[skelsey 103]

If you have selected the approach in the MCDU, the runway itself will be displayed on the ND and should be connected to a CIxx/FIxx waypoint 6-10NM back from the runway -- this effectively gives you an extended centreline, which is where the localiser beam is radiating. 

 

On that note, it is also worth mentioning that it is often good practice to intercept the localiser in selected heading rather than managed nav. Whilst the latter is not completely verboten these days in GPS-equipped aeroplanes, there is still a risk that if the navigation system has drifted slightly during the flight or there is a small mismatch between the final approach track as defined in the navdata by connecting CI/FIxx to the runway threshold co-ordinates, the aeroplane could "parallel" the localiser track in NAV mode whilst descending on the glideslope: as previously mentioned, because the glideslope is only required to be terrain-safe within a small margin either side of the localiser beam itself, this could be dangerous. Either way, it is important to verify using the FMA that you are in LOC | GS once established, not NAV | GS or any other combination of modes!

[Liam123 1]

30 minutes ago, skelsey said:

If you have selected the approach in the MCDU, the runway itself will be displayed on the ND and should be connected to a CIxx/FIxx waypoint 6-10NM back from the runway -- this effectively gives you an extended centreline, which is where the localiser beam is radiating. 

 

 

Is this the letter "D" (I least I think it is) in a circle I'm seeing on the ND? It's all in purple. I remember it disappearing once I got to a certain point, so I'm guessing it's the localiser. Do you think I'd be good arming the LOC switch once I get close to this?

 

Sorry if I'm keeping it basic, I'm not an expert on the Airbus X, though I do appreciate all the help you've given!

[skelsey 103]

57 minutes ago, Liam123 said:

On the MCDU, there are waypoints and just to the right, altitudes corresponding with each waypoint. On the last few waypoints there's a purple star with something like FL050 etc. I believe this is the 'platform altitude'. Are these altitudes the one I'm supposed to descend to?

Yes.

 

To be accurate -- the "platform altitude" for an instrument approach procedure (i.e. the ILS) is the official published altitude for intercepting the glidepath: you find it on the charts (here's an extract from the Zurich ILS rwy 16 chart, showing the 4000ft platform altitude at ENUSO): 

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The other altitudes before that are intermediate altitude constraints on the STAR or in the intermediate approach, and they could exist for a number of reasons: airspace constraints, terrain, minimum navigation altitudes, vertically separating the route from other routes and so on.

 

You determine the altitude for each airport using the charts (see above), and the MCDU navigation database should include the relevant restrictions and altitudes for each procedure if you load it from the database (but be aware that the navigation database can be wrong).

 

10 minutes ago, Liam123 said:

Is this the letter "D" (I least I think it is) in a circle I'm seeing on the ND? It's all in purple. I remember it disappearing once I got to a certain point, so I'm guessing it's the localiser. Do you think I'd be good arming the LOC switch once I get close to this?

No -- that is the "deceleration" point, which is where the Airbus will automatically transition to the Approach Phase.

 

Watching the video, if you look at around 43:20 as the final turn is made, you should be able to see the runway at top left (the white rectangle labelled LSZH 16) and the green line connecting it to IZH03 and ENUSO -- this essentially shows you the extended centreline of the runway. The localiser, by definition (usually!) will be radiating along that path, so you can either leave it in managed nav (which would fly you towards ENUSO and if you had armed LOC at some point approaching ENUSO the likelihood is that LOC mode would become active at some point before ENUSO and turn you on the to the localiser) or, as the person doing the video has done, you could go in to selected heading and position yourself so that you end up on a track towards the extended centreline with the aim of intercepting it some 10-12NM out from the runway.

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[DaveCT2003 2553]

Liam,

 

I want to reiterate what pgreenwo said above.  The Tutorial Flights are designed to answer most all the questions you've been asking and even better they will do so at your own pace.  It's not that we mind you asking questions, not at all.  It's just that you're likely missing a lot of info on things you're not seeing because you don't know they exist, and the Tutorial Flight will help to make you aware of them.  They are really worth going through.

 

My very best.

 

 

 

 

[Liam123 1]

I'll take a look at the videos provided by @pgreenwo above.

 

By the way, that chart is extremely helpful. Where am I able to find such charts with the platform altitudes for intercepting the LOC for each airport? 

[Tom A320 4915]

No, these are the ones:

 

 

 

 

 

 

 

 

 

 

[skelsey 103]

1 hour ago, Liam123 said:

Where am I able to find such charts with the platform altitudes for intercepting the LOC for each airport? 

Navigraph offer a chart subscription, and Aerosoft's chart product is due to be released later this month. Both of these are the LIDO chart format (like the extract above). It's a payware service, but the advantage is that all your charts are in a consistent format and have been optimised for pilot usage.

 

In Europe, charts are published by Eurocontrol (actually, by the state navigation providers) and are available at https://www.ead.eurocontrol.int/eadcms/eadsite/solutions/eadbasic.html (registration required). They're free, but the downside is that the format is not necessarily consistent and the charts themselves are not particularly well-optimised for pilots -- they're provided as a reference for all sorts of users, including procedure designers, ATC, airport planners and so on, so they contain a lot of "raw" data that would normally need to be processed in some way before it's useful to a pilot, and the charts themselves are often cluttered with a lot of extraneous data that's not necessarily relevant or useful to an airline pilot.

[Liam123 1]

Cheers, @skelsey, you've been a big help. I was on approach to LPPT (Lisbon) earlier on, runway 03. I turned just after the "TROIA" waypoint towards the next one and activated the LOC, then started turning towards another airport in the area and completely off-course from my intended arrival airport. I wasn't sure what was going on and the plane was deviating off course, although the diamond on the lower panel was centred. Is it possible I captured the LOC from another nearby airport and simply activated it too early?

[Liam123 1]

Grr, I've been having so much trouble going from Faro (LPFR) to Lisbon (LPPT). Each time it's always the approach. I'm never sure when to activate the LOC, and I'm having trouble deciding which STAR to use on approach for Runway 3. Routefinder gives me " LPFR SID ODEMI A5 TROIA STAR LPPT " Once I get closer to the airport, I activate the LOC switch and even heard the co-pilot say "localiser captured". The plane keeps flying in circles and going to different waypoints. This is really annoying.

 

Could anybody perhaps do a flight from Faro to Lisbon using the above route and tell me where I'm going wrong? 

[Tom A320 4915]

I am sure that you missed the IAF and therefore also the FAF, because still being too high and/or too fast. 

 

Watch your descent closely, use the speed breakes if necessary (or the FMA tells you). Make sure to be at the required altitude according to the maps when getting to the IAF and FAF. 

 

Only if you match both required values correctly the AP is able to capture localiser and glide slope and also follow them. 

[Liam123 1]

One last question before you may close this (I truly do appreciate all the help for a newbie like me!), if you take a look at the airport chart for LPPT (Lisbon), is it telling me that at waypoint "Netvo", I should be at 3000 feet on 26 degree heading to intercept the LOC? Or am I reading it wrong?

 

In addition, what does "P" mean at waypoint Netvo, then the "F" shortly after?

 

By the way I'm using Navigraph.

[FraPre 89]

Hi,

 

P = FAP (Final Approach Point)

F = FAF (Final Approach Fix)

The LOC you must intercept before NETVO for establisht the airplane on the LOC before GS allive/intercept, the GS your airplane intercept at 3000 ft in NETVO.

The LOC can you intercept with an vectoring (ATC HDG instruction), for example +/- 30° to the LOC Course.

 

This is an manual for understand LIDO Charts

 

 

understand_lido_charts.pdf

[Liam123 1]

I'm understanding the tutorials I'm watching, but I just can't get this ILS landing at Runway 03 at LPPT.

 

Here's what I'm doing...

 

F-PLN before take off: LPFR (Faro), take-off runway 28. Route: ODEM8U, A5, TROIA.

 

During cruise, inputting ILS runway 03 at LPPT (Lisbon), gives me some new waypoints so the autopilot follows them. I start descending to 3000 feet and turn the LOC switch on. "LOC *" appears on the PFD in green, the plane keeps flying towards the airport, but at a weird angle and doesn't align with the runway. Once I'm a few miles out, it captures the LOC and begins flying in circles and doesn't align properly. No idea where I'm going wrong.

 

By the way, after I input "Runway 03" and it gives me a STAR, I'm pressing "ESP 8A", although the approach charts on Navigraph says it should be "ESP 9A", not sure if this is contributing to my problem.

 

 

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[DaveCT2003 2553]

Based on 2016-6-12_17-4-55-26...

 

You've armed the Localizer over 20 miles away (over 40 miles, actuially). The Localizer doesn't work that far out.  Wait until you are less than 15 and see how that works.  And follow those waypoints to the next one after ESP before arming the localizer.  That would correct your problem.

 

By the way, I don't think the tutorials specifically discuss ranges (been a long time), but you can see when the arm the LOC and the assocaited range.  Each airport is a little different, but I think the maximum range for a LOC is roughly 20 miles or closer.

 

 

 

[skelsey 103]

Hi Liam,

 

Something is not quite right. Check the ILS ident and frequency displayed in magenta in the bottom left of the PFD:

 

LPST

109.1

12.4NM (in the last screenshot).

 

Looking at the ILS 03 chart at Lisbon, the frequency is indeed 109.1 but the ident should be ILI (as displayed in the box at the top right of the chart). Also, the airfield is clearly within the 10NM range ring on the ND (in fact, at about 6NM) but the DME is reading 12.4. We have a mantra in instrument flying -- "Tune, Identify, Test, Set" (TITS!). After tuning any navaid, you should always identify it by checking the ident (the Airbus conveniently gives you it visually instead of having to listen to the morse!) against the chart and make sure that you are receiving the correct aid. Test (not necessarily so important in a glass cockpit, but if you had a traditional CDI you'd spin the OBS to check the needle moves correctly -- but generally speaking, make sure that the indications make sense. In this case - check the DME against the distance you know you are from the airfield) and then set the correct inbound course. The idea is to avoid (for whatever reason -- either due to equipment unservicability or tuning the wrong frequency etc) accidentally following incorrect indications.

 

At about 12NM on the ND (in your 10 o'clock) is an airfield labelled LPST - Sintra Airbase. It would appear that for some reason the aircraft is picking up an ILS from Sintra, rather than the ILS at Lisbon.

 

What (if any) scenery are you using for Lisbon? Could you try manually force-tuning the ILS through the MCDU NavRad page (use the ident -- ILI -- rather than the frequency and inbound course from the chart). Alternatively -- what happens if you try a different runway? (Maybe try the flight the other way around, departing Lisbon and arriving Faro?)

[Liam123 1]

I'm using Megascenery Earth Portugal which also covers Faro. I completed a flight from EGGP (Liverpool) to LPFR (Faro) a week ago and landed on the ILS perfectly fine on Runway 28. I'm not going to lie, your fourth paragraph threw me off, I'm honestly not sure how to identify by checking the ident, or even understand what you're saying here, haha. I'm not too sure what a DME is or how I pick it up (no offence, it's a problem on my half!).

 

Truth be told, the majority of my successful ILS landings have been mostly through luck rather than definitive knowledge. Usually when I'm approaching an airport, I'll activate LOC when I get within 15 miles, then APPR once I'm lined up. 

 

It did actually cross my mind that I could have been picking up the ILS frequency from a different airport, which is actually quite comical and a slight relief because I was certain I've been messing up somewhere. I honestly must've tried this flight at least 6 times over the past few times, each one having the same result.

 

If I'm able to tomorrow, I'll try Faro to Lisbon using a different runway and post here with the outcome. I can't stress enough how grateful I am to everybody for their help. 

[skelsey 103]

13 minutes ago, Liam123 said:

I'm not going to lie, your fourth paragraph threw me off, I'm honestly not sure how to identify by checking the ident, or even understand what you're saying here, haha. I'm not too sure what a DME is or how I pick it up (no offence, it's a problem on my half!).

 

No problem! We all had to start somewhere. In general, I would recommend you do some reading on basic instrument flight techniques and radio navigation -- it's applicable to all aircraft types and will help you understand better what's going on!

 

TITS (Tune, Identify, Test, Set) is a routine used in instrument flying to make sure that you are receiving the correct VOR/NDB/ILS etc, that it (the ground station) is functioning correctly and also to confirm that your instruments are working properly as well (in an aircraft with mechanical "steam-powered" gauges, the needles could stick, for instance). Any time you use a radio navaid, you should follow that routine:

 

Tune - tune the navaid. The Airbus may auto-tune for you, or you can tune manually in the NavRad page. Check the frequency on the chart (top right panel) and enter it.

 

Identify -- now we have tuned the navaid, we need to check that we are a) receiving it (the ground station could be out of service or faulty, for instance) and b) that we are receiving the correct station. To enable us to do this, each navaid broadcasts its identifier (the three or two-letter code -- on a Navigraph/Lido approach chart, given with the frequency in the top right panel) in Morse Code. You can listen to the ident by turning up the VOR/ILS/NDB (etc) volume on the audio control panel (the morse is given in the top right panel of the chart if you don't know it), and in a smaller/less advanced aeroplane this would be the only way to hear the ident -- but the Airbus (and most modern glass cockpit airliners) "listens" to the audio morse ident for you and decodes it in to its letters, which it displays on the ND (for VORs and ADFs, if you have selected the VOR/ADF switches on the EFIS control panel) or in the bottom left corner of the PFD for ILSs. You should check this identifier against the chart to make sure it matches -- if not, you are receiving the wrong station.

 

Test -- so we've tuned the receiver and checked the ident to ensure that we are receiving the correct station. Now we test to make sure that our instruments are functioning properly. In a glass-cockpit aircraft, this is not so critical because the 'needles' are digital and therefore won't stick (and if there was a problem with the display, we'd probably get some other indication of it) but we can use this step to "sanity check" the information that we have -- in this case, the DME (Distance Measuring Equipment) which is often co-located with a VOR or ILS (and tunes automatically when you tune the VOR/ILS), and tells you how far you are from the station, is showing 12NM but we know from looking at the ND that the airfield is only 6NM away. This should sound some warning bells.

 

Set -- now we have confirmed that we are receiving the correct station, and that our equipment is functioning properly, we move to the final stage -- setting the course we want to follow (for instance, setting the OBS (omni-bearing selector) to the course we want to follow in a "steam powered" aircraft, or entering the radial in to the VOR "CRS" box in the MCDU in the Airbus). For an ILS, we can check that the correct inbound course (compared to the chart) is displayed on the MCDU NavRad page (bear in mind in FS there may be a few degrees difference on an ILS as the magnetic variation has changed over the years).

 

By following this routine each time you use a radio aid -- whether it's an ILS, VOR or NDB -- you should pick up any errors in tuning or problems with receiving the wrong navaid (for instance, it's not impossible for a navaid to not be in the FS database, for the frequency to be wrong or for there to be other issues). However, as I say, what you really need to do is look in to some basic instrument flying principles which should help you understand what's going on!

[Liam123 1]

I understand all of that, thank you ever so much for taking the time out to explain it all! Definitely appreciate it.

[Liam123 1]

Good lord. Finally. What @skelsey said was absolutely correct - the aircraft was somehow getting caught up in the ILS from Sintra Airport whenever I tried to land on Runway 03. I began my seventh flight out of Faro, but this time I planned for a landing on Runway 21 and programmed my flight plan. There was no problem capturing the ILS and I succeeded first time. I'm clueless as to why it was having difficulty capturing the ILS for Runway 03, but I'm just relieved to know it was not all entirely my fault (I'm sure some of it was, but I was certain I was doing the LOC phase wrong!). 

 

Landed successfully from the north on Runway 21. Thank you all, this may be closed!

 

 

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On 9 June 2016 at 11:15 AM, skelsey said:

Hi Liam,

You should arm LOC once you are on a closing heading to the localiser. The localiser in the sim is very reliable, but in real life there are lots of different radio propagation effects that can lead to "false" localiser and glideslope beams: therefore it is best to not to arm the mode until you are a) on a closing heading and b) have been cleared to intercept the localiser by ATC, if applicable.

 

Once you are established on the localiser (i.e. the localiser diamond is centred, or very nearly so), you can arm APPR. You are quite correct in waiting for localiser capture prior to arming APPR: the glidepath is only certified to be obstacle and terrain-safe within a quite narrow corridor either side of the localiser, and therefore you really shouldn't have the aeroplane in GS mode before you are established on the localiser.

 

There are a couple of ATC provisos to arming APPR (and thus GS mode): you must have been cleared for the approach, as opposed to just localiser capture -- "cleared for the ILS"/"cleared for the approach" implies clearance to establish on both the localiser and the glideslope, whereas "report localiser established" implies that you can capture the localiser but must wait for further clearance before descending below your cleared altitude -- in some places this is important for separation against other traffic (landing westerly at Heathrow, for instance, London City departures route underneath the approach path: therefore the controller needs to guarantee that you're not going to start descending until you are clear of that traffic). In this case you will be told "descend with the glide", at which point you can arm APPR. (Hint: if you've not been cleared for the approach or to descend with the glide and you are localiser established with the glideslope needle starting to move down, it's worth a nudge to the controller who has more than likely simply forgotten, rather than waiting until you get too high!).

 

This will depend on where you are in the world -- terrain (especially) and obstacles will affect the altitude to which you can descend and whereabouts you can descend. The only reliable way of making sure you don't fly in to a mountain is to check the charts and follow the altitudes published on them (if you have selected a STAR and approach in the MCDU, the relevant profile should be loaded in the form of altitude constraints, but this should always be checked against the chart as database coding errors can and do happen). 

 

Having said that, broadly speaking 2500-3000ft above airfield elevation, 10NM out is generally a good starting point if terrain/obstacles are not a factor. The standard glidepath is three degrees -- this means for each nautical mile horizontally across the ground you descend (about) 300ft (this is also a good crosscheck when you are established on the ILS to make sure that you are on the correct profile and have not captured a false glideslope lobe etc). Therefore, 1NM out you should be at around 300ft above the runway elevation; 2NM out 600ft; 3NM 900ft; 10NM out 3000ft, 20NM out 6000ft and so on.

 

Hiya, I'm afraid I'm going to have to disagree with/add to your first 2 answers. For clarity, I fly the Airbus for a major European airline.

 

1. While you are correct that you should only arm Localiser when cleared to do so and when on an intercept heading, I will make two further points:

 

a - you must be within 25nm of the localiser before arming it. This helps to avoid false capture.

b - if you are within 17nm and have been cleared for the approach and are on an intercept heading, there is no need to arm the localiser at all. You should arm the Approach, but pressing the APPR push button instead. This leads me to your answer for point 2.

 

2. You should arm the Approach (push the APPR push button) when within 17nm of the ILS, cleared for an approach and on an intercept heading. There is no need to arm the localiser by pressing the LOC push button. The Airbus logic works as such that no glide path intercept is possible unless the localiser is already intercepted. G/S will appear in blue, meaning that it is armed, but the arming criteria requires the LOC* or LOC is achieved. By pressing LOC first unnecessarily, you are committing yourself to a higher-than-necessary workload during a critical stage of flight. If you already have LOC armed or established because you were more than 17nm but less than 25nm out, the APPR push button should be selected at 17nm, regardless of whether or not you are established on the localiser.

 

This is standard operating procedure on the line flying the Airbus.

[skelsey 103]

Fair enough and thank you for the clarifications! I wasn't sure whether the Airbus inhibited GS capture prior to LOC* -- as I am sure you will be aware, some types will capture the glideslope before the localiser and so in these cases it would be wise to be cautious of arming GS mode prior to localiser capture. Thank you for the detail on the ranges and the Airbus logic!