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4 red but on glide slope

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4 red but on glide slope

Old 26th Jul 2022, 11:15
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Originally Posted by Capn Bloggs View Post
PelicanSquawk , IMO you have been unjustly criticised. We need some more info though.

- You say "the chart says MEHt 738 61ft". What chart was this? If it is an official, state chart, I'm surprised it says 738. MEHT for a PAPI/VASI is not contingent on an aircraft type. The PAPI will merely place the eyeballs of who is looking at it at 61ft over the threshold, nothing more. It doesn't matter if it is a Concorde or a Cessna 172.

- What does your ops manual say about transferring to the Visual Aim Point off an ILS? Any mention of transitioning to the PAPI? Mind you, such a thing is, IMO, a stupid idea because it would severely destabilise your approach below the ILS DA. Can your instructor imagine you hauling back on the stick at 200ft AGL to correct the 4 reds you saw?

- What's your stabilised approach criteria? Does it mention that the PAPI overrides the ILS GS?

- What airport was this at? Perhaps the "61ft" is incorrect. It is quite easy to use Google Earth to verify the MEHt if the PAPI can be seen.

- In any case, if the FDAP shows you were on the GS the whole way down, anybody who criticises you or worse, marks you down, is on shaky ground, in my view.

Flight Detent , I don't expect the Yanks to have ICAO markings but the runway above, 05L, has got incorrect markings as well. There should be markings at 150m, 300m then the aiming point markings at 400m. Where is that airport?
Thanks for the reply. I’ll attach below a screenshot from google earth of the runway.

tbh it was a case of me really focussing on nailing the GS because I was getting a bit of criticism before for not maintaining in the last 300ft or so the glide path…but in this case it resulted in 4 reds…I must admit I was much more focused inside and not enough outside…but I feel at a bit of a loss because all the data suggests I couldn’t have maintained the path better, but I’ve been written up as getting low on 4 reds. I really don’t want to have this situation again…and I don’t want to make a big deal of one approach with my instructor because I should just move on.

The chart is navtech and it definitely says 61ft and then a note saying that it’s the MEHT for B738.






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Old 26th Jul 2022, 11:34
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Without wishing to plough through all of the very learned data on this thread, PAPIs are only as good as their last flight check, and that is a very variable standard! As pointed out previously, they are unreliable, at best, below CAT 1 minima, and also depend upon which Aircraft Cat they are calibrated. For instance, NCE 04L is set for Cat D, presumably to prevent them digging their tail into the Med. On my Cat C aircraft, the GS equates to 3 red/1 white.
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Old 26th Jul 2022, 11:40
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Originally Posted by PelicanSquawk
but I feel at a bit of a loss because all the data suggests I couldn’t have maintained the path better, but I’ve been written up as getting low on 4 reds. I really don’t want to have this situation again…and I don’t want to make a big deal of one approach with my instructor because I should just move on.
You should feel aggrieved. Perhaps you guys operate differently, but there is no way I'd let this slide. If for no other reason, to find out exactly what your training captain wants you to do when you reach the DA (at 200ft). This is precisely the point where most people come unstuck these days, with undershoots and overshoots, early flares, late flares, overcorrecting, floating a big cause of prangs. He is your instructor. He's paid for it. It's his job to know this stuff and as importantly, teach you what you need to know to fly safely from 200ft to touchdown.
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Old 26th Jul 2022, 12:09
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Missing the elephant in the room. The ILS GP might not give accurate guidance below 200’ on a CAT 1 ILS, dragging you low if you follow it.
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Old 26th Jul 2022, 12:29
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Originally Posted by Bula View Post
Missing the elephant in the room. The ILS GP might not give accurate guidance below 200’ on a CAT 1 ILS, dragging you low if you follow it.
I guess this is what I was potentially thinking, and trying to establish…the plate does say no cat2 below 100ft though…

any way thanks all for your input and thoughts…I guess I just need to scan better outside if that’s available.

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Old 26th Jul 2022, 13:37
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This is a bit of a bęte noir of mine.
My company was training newbies to fly PAPIs to touchdown-and then wondering why we had so many long landings! Hardly surprising when so much of the TDZ was being wasted.
As mentioned, screen height at the beginning of the TDZ is 50 feet AGL, which in my cat C aircraft pretty much means that when the white line passes directly beneath my gonads (other genital organs are available), the RadAlt should be saying ‘50….’. Usually, at this point the PAPIs show three reds if set to 3 degrees.
So, as Capt Bloggs says, your trainer is erroneous in his assessment if you were in the correct position. I would clarify prior to your next training flight precisely how the trainer expects you to approach this.
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Old 26th Jul 2022, 14:31
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Policy at every airline I have been at is to transition to visual aids when visual. No one needs to be looking in the cockpit at 61 feet or 5 seconds to touchdown other than a peak at airspeed entering the flare.
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Old 26th Jul 2022, 14:50
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PelicanSquawk: The simple answer to this is to ask your instructor to DEMONSTRATE how he wants it done! That may be quite telling......................
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Old 26th Jul 2022, 16:02
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#21 shows it's been recently re-painted - wait for it - from the FAA to the ICAO standard? Hahaha. Just look at the picture. PAPI at 400 m and GS antenna at 330.

With 4 reds, the OP was below glide. That is not a good thing and was called properly, only using the wrong scale.

Being correct and 4 reds happens only on PAPI <> GP 150 m difference (had it on my last flight which we discussed, hence the keen interest today) and this was only 70 m.

Here:
(time stamp 2:50)

Last edited by FlightDetent; 26th Jul 2022 at 17:48.
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Old 26th Jul 2022, 16:59
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Originally Posted by Capn Bloggs View Post
I don't expect the Yanks to have ICAO markings but the runway above, 05L, has got incorrect markings as well. There should be markings at 150m, 300m then the aiming point markings at 400m. Where is that airport?
That was my point. That 05L is called "FAA runway" because it follows the FAA standard of putting the APMs at the second location (300 mtrs) instead of 400 (or even 450 as some others do).

Comes from a country which learned their aviation from the nice coherent FAA regulatory set but then recent years saw a drive of super-aligning with ICAO. Consequently, some runways (all 3000+) are marked with APMs at 300 mtrs, some at 400 mtrs and some even at 450 mtrs. Kid you not, during today's reading I found an airport that has all three choices and the last remaining runway's threshold is yet different as it is displaced by 600 m .

They do keep the PAPI aligned with the markers though. The duality of these being either 300 or 400/450 is nothing new for an 'ICAO' pilot who faces the same two options depending on runway length (2400+ / <.)

When I looked at LAX to see an 'FAA runway' in actual FAA land, markings were as expected. The heart-break moment was seeing the PAPI not aligned with the 305 m/ 1000 ft APM but rather way beyond at 440.
The explanation for this is a) the FAA never said they need to align b) it is provided for large airplanes. I still understand the big jets of Airbus are uniqe to have the GP antenna at cockpit station. Hence my comment the A380 looks specifically designed to exactly match the standard PAPI<>GP offset (as per your drawing).


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Old 26th Jul 2022, 17:31
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Originally Posted by Bula View Post
Missing the elephant in the room.
Depends on the elephant.

Mine's what the acronym stands for.



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Old 26th Jul 2022, 17:42
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Not just the big airbus jets, FD-the 320 has a 6 foot displacement between pilot and antenna…
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Old 26th Jul 2022, 17:42
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Originally Posted by FlightDetent View Post
There is a strong correlation of posts saying the instructor has a wrong idea what needs to be done.

Need the location for AIP charts to prove it.

Yes, the GP can be off. 94% chance this is a case of normal GP and short aim, resulting at 4 reds where 3 reds were geometrically correct. 2W2R for flare would also wrong.




​​​​​
well I think the instructor was right that I shouldn’t have got into 4 reds…as this wasn’t crossing the threshold, it was before. I had my head in the instruments too much, and was trusting the GA indicator. Just confused how it happened when I was on the glide. Interestingly the ofdm data suggests I crossed the threshold at 36ft so that is low…but also that I was on glide.
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Old 26th Jul 2022, 17:44
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fish

I am a much simpler man than some of the evidently big brains who have posted already so despite my experience and age I've found this thread educational but in a way a little inconclusive.

I have been often baffled by the desire of other pilots (usually with little experience on type) to try and hand fly the jet on the glideslope when visual sometimes below minima. Surely it is easier to look out? I note from other posts that the PAPIs aren't terribly accurate and will likely be set to result in touchdown further down the runway than the G/S but I would advocate having an aiming point on the runway which should not move up or down the windshield, isn't that one purpose of the runway markings also discussed above?

In sympathy with the OP's Trainer, maybe (s)he was concerned that once you get to 4 reds and maybe aren't looking at the G/S anymore, then how do you know how much below the 3deg slope you are? I'd be doubtful too about the accuracy of data monitoring information the OP has referred to. What is the sample rate apart from anything else? The trainer has at least succeeded in getting you to think about your technique.

Standing by to be torn apart.
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Old 26th Jul 2022, 18:22
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Have to agree with Alfaalfa.
It was depressing to watch newbies ruin a perfectly good approach below 200ft by looking out of the window and flying the aircraft to what would have been a good landing until they glanced at the needles then either, mainly dived, or climbed to regain the ILS.
When asked why they said it was how they were trained!
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Old 26th Jul 2022, 18:31
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The conclusive and geometrically correct way out of this is
a) figure out the distance of a 3 deg aiming point (300 m or my type)
b) learn to read the different markers and standards to identify the physical location

===== the result just cannot get any easier =====

Field guide A320:
​​​​​​Fly the plane at the front edge of the 2nd marker.

Field guide A330/340
Fly the plane at the far edge of the 2nd marker.

===== if your antenna is within 3 m from pilot eye, use the same ======

(note the absence of any reference to PAPI or GS, FAA or ICAO or other's regulatory reference and runway length considerations).

​​​​​

Last edited by FlightDetent; 26th Jul 2022 at 19:48.
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Old 26th Jul 2022, 19:42
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Originally Posted by alfalpha View Post
I am a much simpler man than some of the evidently big brains who have posted already so despite my experience and age I've found this thread educational but in a way a little inconclusive.

I have been often baffled by the desire of other pilots (usually with little experience on type) to try and hand fly the jet on the glideslope when visual sometimes below minima. Surely it is easier to look out? I note from other posts that the PAPIs aren't terribly accurate and will likely be set to result in touchdown further down the runway than the G/S but I would advocate having an aiming point on the runway which should not move up or down the windshield, isn't that one purpose of the runway markings also discussed above?

In sympathy with the OP's Trainer, maybe (s)he was concerned that once you get to 4 reds and maybe aren't looking at the G/S anymore, then how do you know how much below the 3deg slope you are? I'd be doubtful too about the accuracy of data monitoring information the OP has referred to. What is the sample rate apart from anything else? The trainer has at least succeeded in getting you to think about your technique.

Standing by to be torn apart.

I think this was my issue, basically too much inside on the instruments, and then baffled by what was written because I was too busy not looking outside. I suppose whatever I saw on the instruments isn’t that relevant if I was low just by reference to looking outside…my confusion is how both could have been true. At another runway I guess it would have worked out 2w2r but for whatever reason not at this one…
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Old 27th Jul 2022, 07:50
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An interesting sim exercise we did a few years ago was to set up a generic runway in CAVOK with all the electronic and visual aids available (ILS, DME, VNAV, PAPI, etc.), then keep repositioning onto short finals, failing them one by one until there was nothing but concrete left. This forced people to use a visual aiming point and to refresh the skills that were required on light aircraft, but had fallen into semi-disuse over thousands of hours of precision approaches into major airports.

The whole point of any approach aids, excepting CAT III NDH, is to get you to a position where you can continue visually using an appropriate reference on the runway itself.

It does make me wonder, in the situation that the OP describes, if the PAPIs had been U/S, would his approach and landing been commented upon adversely?
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Old 27th Jul 2022, 08:05
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Originally Posted by FullWings View Post
It does make me wonder, in the situation that the OP describes, if the PAPIs had been U/S, would his approach and landing been commented upon adversely?
Possibly not - but once you are in 4 reds on the VASI then there are no more clues if you get any lower.
Due to different wheel to eye heights on different types, there will always be a mismatch between ILS glide slope indications and VASI indications when very close to the runway - but you should never see 4 reds without comment.
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Old 27th Jul 2022, 08:21
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Originally Posted by Fullwings
It does make me wonder, in the situation that the OP describes, if the PAPIs had been U/S, would his approach and landing been commented upon adversely?
I have no doubt, no. And had he been flying down the 2W2R PAPI with the ILS tuned, he would have been outside tolerance above the glideslope below 200ft.

Pilots should not be jumping from one reference to the other below 200ft.

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