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Where to teach touchdown

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Where to teach touchdown

Old 15th Jan 2022, 19:47
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Where to teach touchdown

An interesting debate is occurring amongst us since I brought back feedback regarding where instructors teach their students to touchdown.

This may seem obvious however CPL students have been taught to use the PAPIs as guidance down the approach and to touch down on the markers adjacent to the PAPIs.

Since attending a standardisation course where it was explained why this is incorrect, I have been gradually retraining students and instructors.

For the benefit of those on here who were not part of the conversation the reasons that I give are:

1. Performance calculations are completed. The quotes LDA is measured from the threshold, not the PAPIs.
2. Students are not landing at a particular point and float down the runway so even less runway is available.
3. PAPIs are for instrument precision approach not visual approaches.
4. PAPIs are not accurate for small light aircraft in the last part of an approach.

The major problem I have is trying to get any student to complete a successful precision landing. This is clearly seen when using an airfield like Shobdon where there is not the luxury of a full length runway.

The problem gets even more complicated when examiners request 2 reds/2 whites and to land on the TDZ

Myself and a colleague who also attended a standardisation course are having difficulty justifying the above and we are struggling where to reference the requirement. Our good work is undone when another senior FI disagrees and tells the students we are talking *ollocks. He is still a friend though!

I would appreciate any help. I am rewriting the courseware which will have a dedicated section to give a full explanation.

Thanks for any feedback.
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Old 15th Jan 2022, 21:12
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Originally Posted by Broadlands View Post
1. Performance calculations are completed. The quotes LDA is measured from the threshold, not the PAPIs.
Yes. But the figures for LDR (landing distance required) in the aircraft manuals are calculated for a screen height of 50ft above the threshold which will result in a touchdown 1000ft down the runway i.e. right next to the PAPI. So both LDA and LDR take into account that the first 1000ft / 300m of the runway are "wasted". Which is not really true because that "waste" of runway is factored into the obstacle clearance. Therefore in my eyes (and in those of my flying school superiors and those of every examiner I have ever flown with) it is a mistake to fly below a PAPI when one exists on the landing runway - independently of the flying conditions.
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Old 16th Jan 2022, 13:12
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To teach the approach using the PAPI, as the standard, to ab initio students is not a good idea. If you are to use the PAPI as a guidance it is important to understand them. Some are just two lights (APAPI) and not four: in which case you are either right or wrong, there is no graduation. The most important thing to understand is that the PAPI is not required to be set at a fixed distance from the threshold, such as 300m nor provide 50 ft above the threshold. The height given at the threshold (MEHT) must be published however and meet defined limits if they are approved for instrument approaches. For these reasons it is most important that the student learns to use the visual clues always available, such as the runway shape, and also be aware of the obstacle heights of the approach and departure profiles.

What is important is that the student learns to assess the touch down from the POH/AFM and factored, for the given conditions on the day, and therefore that the correct airspeed is maintained on the approach. PAPI/APAPI are of course invaluable at night although not essential. The runway lights can give you all that you need regarding the runway shape as guidance.

I think the term "ollocks" is correct.
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Old 16th Jan 2022, 13:47
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Loose thoughts:

Not sure where the confusion that PAPIs are for instrument approaches comes from, but it also needs weeding out.

The concept of TDZ being within the first 1000m or 1/3 runway if shorter is hopefully dead already, good.

PAPI spells 'approach' and not 'landing', well observed.

PAPIs being 'unreliable' down low always souned strange to me. A poor excuse, it's a light beam. Now 'misaligned' or 'inappropriate to use' sounds better.

Following the POH to assure LD matches the published numbers is prime necessity.

Licence applicants should know where and how to land without PAPIs at all, really.

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Last edited by FlightDetent; 16th Jan 2022 at 14:36.
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Old 16th Jan 2022, 14:16
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My question would be - Why would anyone want to drag a light aircraft down a 3 degree glideslope when a steeper approach may be far more appropriate. My base airport has PAPI on two runway ends. I am always well above it on approach and, if I need a short landing, descend though it before touchdown. My approaches are always far steeper than a PAPI glideslope unless I'm flying an ILS or LPV approach.

Fly the aircraft you are in, not the airliner you aspire to fly one day. Touchdown point should be pilot selected based on more factors than where the PAPI would take you.
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Old 16th Jan 2022, 17:54
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Slot of good point that are valid, thanks.
The PAPIs I have calibrated in the past are rarely within spec, and overseas it’s even worse, so I have a fairly healthy sceptical trust in them in any case. Putting the accuracy aside, the issue is students not being able to touch down on a chosen point. By following the lights they will not be at the correct height above the runway at the reference point thereby the flare is later and the touchdown much further down the runway. Yes, instructors are at fault here for not teaching correct use of a reference point.

The AFM data for LDR does allow for the screen height, but on checking Diamond and Piper,, some say the LD must take into account a 50ft obstacle, so although it might be a slight variation in wording, the interpretation is different.

zEhich comes back to the question that with different interpretations and opinions, the correct reference must be quoted to the candidate. A Part NCO flight in a Seneca/42/Arrow does not have to land on the TD, but trawling the specifications and Annex’s I am struggling to give a coherent answer one way or the other.
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Old 17th Jan 2022, 19:41
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Originally Posted by Broadlands View Post
Slot of good point that are valid, thanks.
The PAPIs I have calibrated in the past are rarely within spec, and overseas it’s even worse, so I have a fairly healthy sceptical trust in them in any case. Putting the accuracy aside, the issue is students not being able to touch down on a chosen point. By following the lights they will not be at the correct height above the runway at the reference point thereby the flare is later and the touchdown much further down the runway. Yes, instructors are at fault here for not teaching correct use of a reference point.

The AFM data for LDR does allow for the screen height, but on checking Diamond and Piper,, some say the LD must take into account a 50ft obstacle, so although it might be a slight variation in wording, the interpretation is different.

zEhich comes back to the question that with different interpretations and opinions, the correct reference must be quoted to the candidate. A Part NCO flight in a Seneca/42/Arrow does not have to land on the TD, but trawling the specifications and Annex’s I am struggling to give a coherent answer one way or the other.
Do you teach CPL/ATPL(F)/MPL students to become GA pilots flying C206s etc. in the bush (or anywhere else!), or do you teach them with the aim of flying as AoC/Airline pilots. If it´s the latter, then you should teach them to use the PAPIs/VASIS as we do - and of course teach the variety and the pitfalls of the various systems. Understanding license requirements vs objective is not simple. Depends on the ATO primary objective I guess. Good question.
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Old 17th Jan 2022, 19:52
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Surely the PAPIs are aligned with eye height. Therefore they are bound to have different clearance limits depending on whether you are flying a 737/747 or a light aircraft. The problem compounds when you are teaching future airline pilots to land a typical light aircraft abeam the PAPIs hence using up considerable runway behind you. It is obviously important to be disciplined with touchdown aiming points when flying swept wing jet transports with finely calculated landing performance versus plonking it down on the numbers in a general aviation machine. Incidentally even in airline world we teach to ignore the PAPIs below 200 feet (within reason!). Interesting debate though.
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Old 17th Jan 2022, 21:02
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Do you teach CPL/ATPL(F)/MPL students to become GA pilots flying C206s etc. in the bush (or anywhere else!), or do you teach them with the aim of flying as AoC/Airline pilots.
What on earth is the difference? The PPL phase teaches the basic skills. If the ab initio training has been completed correctly then adding complexity and all else, that has special skills, should be a straightforward addition of skills. I'm baffled how we could teach 'bush flying' in middle England or anywhere similar.

Incidentally even in airline world we teach to ignore the PAPIs below 200 feet (within reason!)
And so it should be in a C150 and mostly it is.
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Old 18th Jan 2022, 13:58
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Originally Posted by Fl1ingfrog View Post
What on earth is the difference? The PPL phase teaches the basic skills. If the ab initio training has been completed correctly then adding complexity and all else, that has special skills, should be a straightforward addition of skills. I'm baffled how we could teach 'bush flying' in middle England or anywhere similar.



And so it should be in a C150 and mostly it is.
Well you can obviously teach whatever you feel like. However for the aspiring student, with one primary goal in front of him, the relevance of learning to use PAPI/VASI on the visual segment (when available) is sensible. Airports with this type of visual aid available, likely won´t create any great concern with landing performance in a light aircraft. Teach the skills that will benefit the student in the future, not just for passing the issuing of the license. Good habits and general understanding of the benefits and pitfalls of available aids are long term benefits.
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Old 18th Jan 2022, 14:06
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Originally Posted by olster View Post
Surely the PAPIs are aligned with eye height. Therefore they are bound to have different clearance limits depending on whether you are flying a 737/747 or a light aircraft. The problem compounds when you are teaching future airline pilots to land a typical light aircraft abeam the PAPIs hence using up considerable runway behind you. It is obviously important to be disciplined with touchdown aiming points when flying swept wing jet transports with finely calculated landing performance versus plonking it down on the numbers in a general aviation machine. Incidentally even in airline world we teach to ignore the PAPIs below 200 feet (within reason!). Interesting debate though.
Your point is valid, however you could equally consider that you´ve got plenty of runway ahead of you, on an airfield that is equipped with PAPIs, when you arrive in the typical light aircraft. Whatever the aircraft performance handbook is based on, is ultimately going to be a good argument to follow.
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Old 18th Jan 2022, 16:01
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Agreed Klimax!
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Old 18th Jan 2022, 18:04
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Well you can obviously teach whatever you feel like.
No, you cannot.
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Old 18th Jan 2022, 20:06
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Originally Posted by Fl1ingfrog View Post
No, you cannot.
Roger that.
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Old 20th Jan 2022, 07:38
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Brakedwell

One solution is to teach both techniques are appropriate depending on the circumstances. So for the ab initio phase keep it simple. Aiming point technique etc and don’t waste useable runway behind you on landing. Emphasise that if landing on a limiting runway care is needed eg excessive approach speed, longer than normal float.

Of course the student needs instruction on how to use and interpret landing data. Is the data for the ground roll or assumes 50 ft above the threshold? Those are the two I’m familiar with perhaps there are others. Always happy to be informed, corrected etc.

For an aspiring CPL holder explain the techniques employed on a jet transport may, or may not, be the same. In that context explain that landing “on the numbers” is not correct in this type of operation but it might be necessary flying a light aircraft onto a short runway. In particular I would suggest any “ducking under” will likely lead to swift admonishment from the trainer! In that context I always understood that if PAPIs are available then they should be used. I don’t recall an official height below which they can’t/shouldn’t be used but as Olster said 200 feet seems reasonable. Of course that generally corresponds to Cat 1 decision height. Anyway, hope that helps. Interesting discussion.

ps to further confuse matters some approach plates tell that you that the visual guidance and instrument procedure don’t coincide.
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Old 20th Jan 2022, 08:44
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I'm with the frog on this one. In light aircraft 4.5 to 5 degrees for the slope during basic training, using the runway shape to judge height on base or final. At night, the runway edge lights and threshold lights at each end should give the same picture. Any PAPI (or LITAS which we still have) to be a back up to the picture.
Teaching 3 degree approaches should be during the commercial training phase, or as advanced training for PPLs, at a suitably long runway. If we used 3 degrees on our prevailing straight in, we'd be around 700 feet above a built up area outside our ATZ, in Class G, and we don't have any instrument approaches as an excuse for being so low. That would also put us too close to the trees and steel rugby posts on very short final, culminating in a long landing on our relatively short tarmac.
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Old 21st Jan 2022, 06:54
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Originally Posted by MrAverage View Post
I'm with the frog on this one. In light aircraft 4.5 to 5 degrees for the slope during basic training, using the runway shape to judge height on base or final. At night, the runway edge lights and threshold lights at each end should give the same picture. Any PAPI (or LITAS which we still have) to be a back up to the picture.
Teaching 3 degree approaches should be during the commercial training phase, or as advanced training for PPLs, at a suitably long runway. If we used 3 degrees on our prevailing straight in, we'd be around 700 feet above a built up area outside our ATZ, in Class G, and we don't have any instrument approaches as an excuse for being so low. That would also put us too close to the trees and steel rugby posts on very short final, culminating in a long landing on our relatively short tarmac.
Totally with you on the PPL training - which is, as far as I´m concerned, purely a license training phase, on the track to become an airline pilot (if that´s the goal).
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Old 21st Jan 2022, 14:23
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Originally Posted by MrAverage View Post
I'm with the frog on this one. In light aircraft 4.5 to 5 degrees for the slope during basic training
Got me thinking that in the early days on SEP trainer A/C the target V/S was 3 mps = 600 fpm at 140 km/h indicated.

How come the same V/S gives me two-white/two-red these days at 120 knots over the ground? I certainly don't remember the PAPI showing all white then.

Touché, quick check with AIP reveals it is still set for 4,5 deg, twenty years later since my last visit. .

Last edited by FlightDetent; 22nd Jan 2022 at 09:45.
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Old 21st Jan 2022, 16:33
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Originally Posted by FlightDetent View Post
Got me thinking that my SEP trainer was V/S 3 mps = 600 fpm at 140 km/h. Today I do the same for 130 KIAS with 10 kt HW. How come the PAPIs were not all white, IIRC? Touché, quick check with AIP reveals PAPI set at 4,5 deg.
The V/S varies from day to day depending on many variables - the bloody PAPI or glide slope or visual aims don´t. Rules of thumb are great for basic training, but later on in life (airline world) the resources are better invested focusing on other more important things, I´m sure we´ll all agree on that. There are PAPIs/VASIS and a hole lot of other aids to be used, and they are all used by professionals, so they should be taught to be utilized accordingly. CPL and forwards, towards the ME-IR and subsequent Type Rating, is a great time to create good habits.

Last edited by Klimax; 22nd Jan 2022 at 08:05. Reason: talking about tombs instead of thumbs.. ;-)
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Old 21st Jan 2022, 20:18
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Lost in translation, my bad. But I like your 'rules of tombs'. Try to edit the post now.


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