Go Around decision with B737

[Marc Sieffert]

Hi, a few days ago I landed with my B737 Zibo in EGKK (Gatwick). I am using Noaa weather and there was a terrible fog... Actually I started to see the rwy when I was at 45-50 meters height... but I switched on autoland... So my question is, I read that actually the decision height for Go around is 200 feet with autoland or without autoland (I think there is no difference in the decision height...). Would it have been correct to Go around without seing the Rwy at 200 feet?

[Andreas Fuchs]

Please search for "Low Visibility Procedures", "ILS category II", "ILS category 2", "ILS category III", "ILS category 3". Should give you all the answers.

[Joshua Jenkins]

(Disclaimer: I'm not a real-world pilot so this post is just from my understanding and research. I'm sure one or more of the many actual pilots on VATSIM will probably correct something or the other with my response.)

Depends on if you were on a CAT I, CAT II, or CAT III ILS approach (not sure which ones Gatwick has). A CAT I is not suitable for autolanding and generally has a DA (decision altitude) of 200 feet, although it may be slightly different at various airports. If you don't see the runway by this altitude, you execute a go-around. If you see the runway you disconnect the AP and hand-fly it in. A CAT II ILS, on the other hand, is suitable for autoland.  If you were flying the CAT II approach you still will have a DH (decision height). The difference between a DA and DH is the DH uses the radio altimeter rather than the baro altimeter so in theory it should be more accurate. Again, if you don't see the runway by the DH on a CAT II approach you go around, however if you do see the runway or runway lighting you can continue with an autoland (typically the minimums on a CAT II or CAT III approach are too low to safely disconnect the AP and hand-fly the landing). That brings us to a CAT III approach which has even lower DH, or depending on the airport, no DH at all. Again, same principle applies to these as the others, if there's a DH you need to see the runway or approach lighting by then, if there's no DH then just let the plane do it's thing (as long as you're monitoring it of course). Often, an airport will have both CAT I and CAT II (and/or CAT III) all on the same NAV frequency, so it's just a matter of briefing the approach and having the right equipment on your plane to fly it.

 

Edit: Here's an excellent video on the topic 

 

Edited March 5, 2021 at 09:30 PM by Josh Jenk

[Torben Andersen]

You don't mention which runway you used.

Descition height is 100' (rwy08R) or radioaltimeter 96'. 45-50 meters is like 135'-150' , so you should be good. If your altitude was 45-50 FEET the you should do a go-around for a CAT II. If you cand do a CAT IIIa approach you just might be able IF the altitude was 50'

 

[Lauri Uusitalo]

On 3/5/2021 at 10:28 PM, Torben Andersen said:

If you can do a CAT IIIa approach you just might be able IF the altitude was 50'

 

In real life you can not do CAT II/III approaches unless the airport is currently using Low Visibility Procedures. I am not sure if these are in use Vatsim.

[Joshua Jenkins]

6 minutes ago, Lauri Uusitalo said:

In real life you can not do CAT II/III approaches unless the airport is currently using Low Visibility Procedures. I am not sure if these are in use Vatsim.

Yes they are used on VATSIM to what extent we can when needed. For example, you can absolutely use CAT II/III approaches or special taxi routes, but you might not be able to simulate things like follow-me cars and whatnot. Also, IRL pilots can (and do) use CAT II/III ILS approaches even when the airport is not under low vis procedures because they need to remain proficient (there's a number per time period needed but I'm not sure what it is off the top of my head). The only thing is, you need to inform/request permission from ATC if you plan on using a CAT II/III approach under regular conditions because of the increased separation needed and different holding points on the ground, etc. etc...

Also, there is no rule to fly with real life weather on VATSIM so a pilot may be flying with thick fog and need to autoland where the weather IRL might be CAVOK.

[Torben Andersen]

18 minutes ago, Lauri Uusitalo said:

In real life you can not do CAT II/III approaches unless the airport is currently using Low Visibility Procedures. I am not sure if these are in use Vatsim.

Josh just beat me to it 🙂 Anyways, ATC isn't always present, so then you can do whatever...Don't know if that was the case?

Edited March 8, 2021 at 07:48 AM by Torben Andersen

[Lauri Uusitalo]

29 minutes ago, Josh Jenk said:

The only thing is, you need to inform/request permission from ATC if you plan on using a CAT II/III approach under regular conditions because of the increased separation needed and different holding points on the ground, etc. etc...

And this permission may not be provided if the airport is busy and can not accommodate e.g. increased separation.

Of course we can do what we want as this is a virtual environment. But I assumed OP wanted to simulate real life situation when asking if missed approach would have been correct thing to do, as it would have been.

If you have briefed the landing as CAT I, and at 200' you find that the clouds are lower, you are not allowed to "aaah bugger, let's do CAT III autoland".

Edited March 8, 2021 at 08:14 AM by Lauri Uusitalo

[Torben Andersen]

@Lauri: I agree with you per se, however in our virtual environment the weather is set by the pilot. If ATC was present and LVP was not in use, you can't as controller see, if the pilot did an CAT III autoland. I would probably make a go-around. If I was pressed for time (wife calling or whatever) or fuel I would perhaps do a CAT III.

cheers

[Joshua Jenkins]

10 minutes ago, Lauri Uusitalo said:

And this permission may not be provided if the airport is busy and can not accommodate e.g. increased separation.

Of course we can do what we want as this is a virtual environment. But I assumed OP wanted to simulate real life situation when asking if missed approach would have been correct thing to do, as it would have been.

If you have briefed the landing as CAT I, and at 200" you find that the clouds are lower, you are not allowed to "aaah bugger, let's do CAT III autoland".

Agreed. But as Torben mentioned, that's up to you as a pilot to follow those restrictions and execute a go-around or land anyways. Unfortunately (or fortunately depending on how you look at it), an ILS signal can't get interrupted by another aircraft on the ground in any of our simulators, and we don't have hundreds of lives in our hands relying on us not making a mistake, despite often imagining we do.

[Tobias Dammers]

Aircraft getting in the way don't interrupt an ILS signal IRL either - otherwise, having multiple aircraft on the same ILS approach at the same time would not be possible.

[Andreas Fuchs]

3 hours ago, Tobias Dammers said:

Aircraft getting in the way don't interrupt an ILS signal IRL either - otherwise, having multiple aircraft on the same ILS approach at the same time would not be possible.

Oh yes, they do! I see fluctuating LOC and GS indications all the time in the real world.

That's why LVPs have to be in force, before CAT II or even CAT III approaches can be flown in the real world. Aircraft near the antennas definitely do affect the beams of localizers and glideslopes. LVP means that "protected areas" are created to avoid aircraft obstructing the signals, especially of the glideslope atenna. And that's also the reason why you need bigger lateral separation on finals when LVPs are in force: the preceding aircraft must be well clear of the runway before the succeeding plane comes close to the ground.

[Simon Kelsey]

5 hours ago, Tobias Dammers said:

Aircraft getting in the way don't interrupt an ILS signal IRL either - otherwise, having multiple aircraft on the same ILS approach at the same time would not be possible.

As Andreas says, interference from aircraft (or vehicles) can very much affect the localiser and glideslope beams -- this is why the CAT II and CAT III holding points are much further back from the runway. At Heathrow I seem to recall it is/was standard for aircraft following an A380 on approach to be given the RNAV (weather permitting) rather than the ILS as a matter of routine because for whatever reason the size of the A380 was causing disturbances to the ILS for following aircraft (whether during the approach or maybe whilst vacating etc, I'm not sure).

This video is an excellent demonstration of the dangers of autolanding when the airfield is not in LVPs:

The B777 crew had performed an autoland/rollout -- the cause of the excursion was, I believe, determined to be due to a BAe 146 which had departed ahead passing over the localiser array which caused the beam to deform...

[Andreas Fuchs]

Some facts for the Singapore mishap: http://avherald.com/h?article=445873f3/0001&opt=0

Luckily we don't simulate this in any of our FS software.

[Tobias Dammers]

Oh boy... yes, now that I think about it, that does make sense, after all an aircraft is a big metal tube...

Though technically the signal doesn't get interrupted, "only" disturbed, so the NAV equipment will still pick up *something*, it will just be a bit wrong.

[Andreas Fuchs]

A bit? I have seen several types doing strange things...believe me.

[Andrew McCabe]

Interesting thread and really good to get the perspective of the RW and the experienced simmers.  Out of interest, does FSX or P3D actually model the effect of obstructions to the LOC or ILS beams ?

 

Andrew

[Andreas Fuchs]

46 minutes ago, Andrew McCabe said:

Out of interest, does FSX or P3D actually model the effect of obstructions to the LOC or ILS beams ?

No, I never heard about this being simulated.

[Robert Shearman Jr]

6 hours ago, Andrew McCabe said:

Interesting thread and really good to get the perspective of the RW and the experienced simmers.  Out of interest, does FSX or P3D actually model the effect of obstructions to the LOC or ILS beams ?

 

Andrew

No, nor X-Plane nor MSFS2020.  To do so would require not only a high degree of radio-wave physics modeling, but, also the proper AI to read the weather and understand that CAT II and III approaches may be in place, and to direct AI aircraft to hold short of the ILS short-lines accordingly -- and/or to determine a reasonable (or user-defined) threshold for AI aircraft who would fail to do so.  Remember, these sims at their cores are not designed with VATSIM in mind.  Maybe some industrious fellow would go out of their way to create an add-on or plugin to model this, but, it comes into play so infrequently that I can't see the development and testing time being worth it.

[Andrej Lippay]

This obstruction that was stated here can be nicely seen on a following video. This is CAT I landing, and there is an airplane taking off from the same runway. You can see how "wobbly" LOC is, that is caused by airplane taking off. Hence why LVPs are in place.

 

Best!

Edited March 23, 2021 at 12:32 PM by Andrej Lippay