FBW Fly By Wire a320 ILS questions

Hi all! I have been flying the FBW a320 and have all the basics figured out. I put the DA baro ect. into the perf but a number of small problems have been occurring. One is that it often says that ILS cat 2 is engaged.

How do I make it cat 1? Another is that a couple of times I have been getting too low terrain warnings despite being perfect on the glidescope. Any idea why, and is this tied to the wrong cat of ILS being selected?

Also, a couple of times I’ve had the managed speed never recognize I was on approach and kept the speeds at 250 kts, though this seems to be more rare now…and anticipate it by bringing the speed down on selected speed if I suspect something is up.

One issue might be that I have been areas of high elevation such as Denver, but think I have full flaps and all the right switches have been correct outside the mcdu which I suspect I’m messing up. Maybe I forgot full flaps one time, but don’t think so. Any help would be great, especially on the first two issues.

You can’t make it CAT I and it wouldn’t make sense.
The AP automatically uses the lowest possible minimum for the current aircraft/runway combination.

The terrain warning can come on if you are e.g. flying too fast at a too low altitude and/or extending the flaps too late etc.

If the speed doesn’t drop below 250, the approach mode in the MCDU isn’t active.
If the activation doesn’t occur automatically, you have to activate it manually.

Don’t understand your Denver problem.

Ok got it on the first question. I thought cat II was autoland, but that are more of the cat III subcategories. Got them mixed up!

I’m pretty sure I’m getting the too low terrain alerts when I already have full flaps, but may have put them on too late…usually I am doing final at 140 kts. Hopefully didn’t forget full flaps.

One more question…on cat II I still use DA/baro and not DH/radio right?

Thank you both for your help…so on FAA charts I would select the second number to right on ILS column with no parenthesis right? So for LAX 25L (https://skyvector.com/files/tpp/2107/pdf/00237IL25L.PDF) DH would be 200, which I put in radio?

Again thank you so much!

Autoland and ILS Category aren’t connected in any way.
The AP can land on a CAT I runway as well and on some aircraft you can fly CAT III without AP.

The AP also doesn’t care if or what minimum you select.

Generally once the minimum is below 200ft, you are switching from baro minimum (altitude) to the much more precise RA minimum (height).

KLAX 25L is only a CAT I approach, hence you use the 304ft baro minimum DA, not 200ft DH.

For CAT I you don’t use DH.

The RA is only active below 2500ft and if it turns out at this height that it fails, you have to rebrief the and reset the minimum. This does increase the workload.

Even worse, many airlines prohibit resetting of the minimum below 1000ft.
If the RA fails below this altitude you need to go around.

The most important reason to use DA is the terrain.
CAT I approaches have much lower requirements concerning the terrain in front of the runway.
Using the RA and DH might trigger the minimum callout way too early.

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Have you read the part about the terrain?
I’m not aware of a CAT I RA minimum on an approach chart. Do you have an example?

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Which would require a premature ‘contact’ / ‘continue’ etc. callout, which would be rather distracting shortly before the flare.

PZL104 is right. When visibility is that low, requirements with regards to terrain avoidance are that high.

Ignoring the GPWS under such circumstances because you didn’t understand what the chart was telling you is not proper airmenship. That’s fine in a simulator, but repeating a faulty claim doesn’t make it right.

I suppose you’re right… it’s probably why I keep my flying to stay in MSFS… so many things to learn. Hahaha. My bad, I’ll retract my statements. then. Thanks for pointing it out.

I just got used to use the TERR radar on my ND when flying under low visibility with terrain hazard. If I see red, I know that I need to be aware of it to make sure I don’t fly too low and ignore any GPWS minimum callout, unless it’s a terrain warning. But yeah, all of my experience is only on MSFS really.

So as I get it, on an A320, I am using cat II or cat III (I’ll stick to cat II for this discussion). In most cases I use DH, but sometimes DA if there is terrain. Did I understand that right? How do I know when I need to use DA instead?

As for the “too low terrain” when I am perfect on the vertical glidescope and at about 140-150 kts, is this most likely due to flaps/speed or could it be something I put in wrong in the MCDU such as DA rather than DH?

I think if there’s a terrain hazard on the approach, the ILS Cat will never be certified to CAT II or CAT III in the first place. If it’s already certified with CAT II or CAT III, it’s usually clear of any terrain hazard on approach and you can safely use the DH.

If there are terrain hazard that requires you to have a DA as the minimum, then the ILS will never be certified for CAT II or III, always on Cat I.

If the approach chart says CAT II or III, then the terrain clearance is sufficient to use DH (but if you only fly down to a CAT I minimum you use DA)

If it’s CAT I only, as in your KLAX 25L example, you have to use DA.

The terrain warning has nothing to do with the minimum.

The advice already given here is spot on. I’d only like to add that on a real Airbus the autopilot runs a sequence during approach at which it is confirming to itself that the plane is in the process of landing (and hence being close to the ground is fine). It allows its internal systems to execute the phase of flare at the very end (which in terms of computing power is very complex, a staggering 18 million calculations and decisions per second, mind you).

Now when the AP is deciding that the plane is in landing configuration it needs to be absolutely sure because it’s also going to interpret pilot input on the sidestick differently than during other phases of flight. What you can do to help make this decision is getting the plane ready to land in the most obvious way. You approach it with slats extended (so flaps 1), confirm the MCDU activated approach phase, keep extending those flaps as you slow down, put your gear down in time. Arm spoilers and arm the autobrakes to medium. And after all that, press the Take-Off Configuration Test one more time, just as you do before take-off. The ECAM will give you a similar short checklist with all proper landing settings confirmed. My bet is you’re missing out on this last single action and the plane is unsure you want it to land before it rounds up its own internal safeguard calculations.

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You’re both wrong because you’re both focusing on the wrong hazard. It is indeed called a terrain radar, making you focusing on terrain which is only logically. However an approach path can also be cluttered with power lines, buildings or other obstacles that are too small to be picked up by your terrain radar. Hitting one of those however will kill you just as much as a mountain would. :wink:

Why would you use the TO CONFIG button on approach? That’s new to me and it doesn’t make sense.

Oh thanks, I did not know about TO config.

Skyvagrant, are you saying that I could be on the glidepath but getting a terrain warning because there is something like a powerline?

Also…how do I know that KLAX is cat I only (or any other cat) on an FAA approach chart…I don’t see CAT on the FAA chart?

Yeah I’ve always thought is a confusing button too. I guess you just have to remember it as a TOGA configuration test, but it serves indeed as a landing configuration test too. It will bring up a different checklist on your ECAM.

This doesn’t make any sense since a CAT I approach has the same vertical profile as a CAT II or III approach.

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