Landing Performance on a sloping Runway

[Jwscud]

I fly fairly regularly into an airport with a shortish runway (2000m) and fairly steep upslope in the prevailing landing direction. I had a disagreement after landing with the Captain I was flying with regarding landing performance. I flew a stable approach aiming at the touchdown zone and on the glidesope/PAPI all the way. This led to the GPWS "50" callout after passing over the piano keys. He felt I was "high", despite me touching down abeam the PAPIs.

He said for landing performance in all cases one should cross the threshold at 50'. I am aware this is the standard screen height and landing performance is based on this. However, with a steep upslope and the 3° Glide/PAPIs leading you to the touchdown zone, my figures calculate for this particular runway on a 3° slope the threshold is 16' below a "flat" runway profile, so if making a 3° approach aiming at the TDZ, one crosses the threshold at 66'.

I have looked in my copy of Swatton, and it doesn't really broach the subject. I would welcome opinions and references as it is an area I could do to improve my knowledge on.

[JammedStab]

Usually transport aircraft are certified only for plus or minus 2% runway slope with special approval required for more. I seem to remember an Alaska L382 carrier having FAA approval for a much steeper runway slope at certain unique airports.

A lot depends on airport versus aircraft type. While not specifically about runways with a slope, we used to land turboprops on a fairly short snow covered runway and ignored the PAPIs close-in as the would have you land far down the runway. In fact on most of the shortish runways, we would "dip" the PAPIs when close-in. It was never a problem being less than 50 feet over the threshold in those types with a nose low attitude on approach.

No doubt some people will disagree on doing this.

[ZAZ]

Correct me if I am wrong but isn't that why we have P charts. You know the ones in the AFM marked Soft and wet, Dry and down slope, Dry and short. And in the end its all done by the Mk 1 eyeball and Type 2 brains, Given the optical illusory effects of a sloping runway that we are always warned to compensate for. 2c.The pap I sets u at 3 degree so if slope is 2 down u visually compensate keep sped correct and be aware going downhill will take longer to stop. If u did same thing uphill you would land very flat or maybe on the nose wheel so at flare u raise the node a bit more.

[compressor stall]

What is the MEHT for your aircraft and the PAPI on that runway?

The PAPI is usually set up for the largest ac type to use that Rwy.

[chimbu warrior]

It is all about bringing the aircraft to a stop safely in the landing distance.

Ask your "Captain" how he would handle the situation if he had to land at the same airport, but in the opposite direction; would he cross the piano keys at 50 feet and then float for 1000 metres - not such a good idea on a 2000 metre runway.

If you followed the glideslope and PAPI why would he think you were not on the correct profile?

I have landed on lots of sloping runways (although not in transport category aircraft) and none of them had PAPI or VASIS, and the technique you have described worked perfectly.

I would prefer to fly with you than him.

[cosmo kramer]

Much more important question is, why didn't he ask you to go-around, if he felt you were outside parameters??

Below 200 feet, you shouldn't follow any landing aids anymore (including PAPI), instead fixing the aim point in the windscreen and keeping it there until flaring. Which is what it sound like you did.

You don't specify your type. But dipping below the "visual profile", it NOT recommended by Boeing! Changing you profile in the last few hundred feet, may lead to a messed up flare and a long landing. Landing performance takes normal profile and flare into account, so it's not necessary at all.

From what you describe, it seems like you did it right. And if you didn't, the question remains why the captain in question didn't order a go-around.

[A Squared]

I seem to remember an Alaska L382 carrier having FAA approval for a much steeper runway slope at certain unique airports.

Yes, up to 8%

[Gysbreght]

From a performance engineer's perspective, the captain is quite correct.

The certification landing distance is measured from a height of 50 ft above the runway. Perhaps that is not so relevant because the procedure for determining the certification landing distance is not representative of normal landings in service.

When landing on a 'shortish' runway the threshold should be crossed at a height of between 30 and 50 feet. Ideally the Papi should be set to provide a threshold crossing height of 50 ft. On a runway with a 'fairly steep upslope' it should also be set at lower approach path angle to maintain (if possible) the same screenheight-flare-touchdown geometry and optical perception of the runway as on a level runway.

Just my opinion.

[JammedStab]

Yes, up to 8%

Any special techniques(or at least different from normal) used?

[vilas]

Jwscud
Below 50 ft. you go by what you see and feel. With a slope towards you, the rate of descent induced by flare is in effect reduced by rate at which runway is rising.you get a feeling that you have not flared enough as the runway rushes towards you so subsequent change of attitude needs to be sooner than normal runway. Opposite of this happens when it slopes away from you. You feel you have ballooned and there is a bit of unflare required. Ultimately you need to follow the slope during flare and landing. If you do not cater for this you are likely to get harder or firmer landings upslope and landing deep with downslope. IIRC Abu dhabi runway is an example of upslope. Bombay runway 14 has a downslope after some distance from threshold. If you do not touch down early it gives a feeling of ballooning.

[A Squared]

Any special techniques(or at least different from normal) used?

Not really. Just fly an normal approach to your touchdown point. Usually these runways don't have any kind of approach path indicators, so you're eyeballing your descent. One thing that's important is to be ready to come in with a handful of power after touchdown to keep your momentum going. Getting stopped is no problem, but you definitely don't want to stop until you're on the parking area. Getting started again after stopping halfway up the runway would be a challenge.

Taking off you want to keep in mind to not pitch to a normal climb attitude to briskly on lift off, as it's a lot easier to drag the tail. It's really pretty odd to see your VSI showing 1000+ fpm down as your breaking ground.

[A Squared]

On a runway with a 'fairly steep upslope' it should also be set at lower approach path angle to maintain (if possible) the same screenheight-flare-touchdown geometry and optical perception of the runway as on a level runway.

So on one of my 8% gradient (4.5 degree slope) runways You should start your approach below the touchdown and fly up to it at a 1.5 degree up "glide" path? :eek:

[Gysbreght]

In theory, yes. In practice, obstacles and terrain in the approach area may not allow it. Approaching in level flight would be equivalent to approaching a level runway on a 4.5 degree glideslope, i.e. still a steep approach requiring a greater flare height (relative to the runway) than a normal approach.

Vilas above expressed it perfectly in somewhat different words.

P.S.1
It should be obvious that I'm talking of the final stage of the approach to the runway.

P.S.2
Conversely (and perhaps less controversial), for landing on a downsloping runway, the PAPI should be steeper than for a level runway.

[A Squared]

In theory, yes.

Well, having actually done extreme gradient ops, I can tell you that's not the way it's done.

P.S.1
It should be obvious that I'm talking of the final stage of the approach to the runway.


Actually, if you look at what you wrote you were talking about how to set the approach slope guidance. That's not the "final stage" of the approach.

[glendalegoon]

READ THIS:

(c) Runway and terrain slopes illusion. An upsloping runway, upsloping terrain, or both, can create the illusion that the aircraft is at a higher altitude than it actually is. The pilot who does not recognize this illusion will fly a lower approach. A downsloping runway, downsloping approach terrain, or both, can have the opposite effect.


NOW, the above is from the USA FAA Aeronautical Information Manual. Illsusions of flight.

The captain felt high, it was an illusion. SEE ABOVE.

I knew this stuff before I had my private pilot checkride. Where are you flying?

Piano Keys? we call them threshold markings.

[Gysbreght]

I can tell you that's not the way it's done.Well, I read you: "Just fly a normal approach to the touchdown point".

[A Squared]

The captain felt high, it was an illusion. SEE ABOVE.

That could be, maybe it did contribute to his response.

Now we only have one side to the story here, but according to the OP, he was *on* the PAPI, and touched down *at* the touchdown markers. If all that is true, and he was on speed, there's really not a lot to (legitimately) criticize about the landing. To claim that an approach and landing which was on speed (an assumption), and nailed the PAPI, and touched down at the touchdown markers was somehow defective because the plane was 66 ft over the threshold vs 50 ft is inane.

[A Squared]

Well, I read you: "Just fly a normal approach to the touchdown point".

Right. By that I mean a descent which is inclined 3 degrees to the horizontal, not 3 degrees to the runway. Not sure how you infer that "normal approach" would be flying up toward the runway.

[Gysbreght]

Yes, I understand that. We're obviously not communicating on the same wavelength.

My concern is about flare height and required landing distance. I would like to understand how PAPI/VASI take account of runway slope. Perhaps the following is relevant (emphasis mine):

AIM Chapter 2. Aeronautical Lighting and Other Airport Visual Aids
Section 1. Airport Lighting Aids
(...)
2-1-2. Visual Glideslope Indicators
a. Visual Approach Slope Indicator (VASI)
1. (...)
2. Two-bar VASI installations provide one visual glide path which is normally set at 3 degrees. Three-bar VASI installations provide two visual glide paths. The lower glide path is provided by the near and middle bars and is normally set at 3 degrees while the upper glide path, provided by the middle and far bars, is normally 1/4 degree higher. This higher glide path is intended for use only by high cockpit aircraft to provide a sufficient threshold crossing height. Although normal glide path angles are three degrees, angles at some locations may be as high as 4.5 degrees to give proper obstacle clearance. Pilots of high performance aircraft are cautioned that use of VASI angles in excess of 3.5 degrees may cause an increase in runway length required for landing and rollout.

[cosmo kramer]

Quote Jwscud:
I would welcome opinions and references as it is an area I could do to improve my knowledge on.
As I was looking in the FCTM for other reason, I remembered this thread.
Here you go:
FCTM:
Threshold height is a function of glide path angle and landing gear touchdown target. ...
Special attention must be given to establishing a final approach that assures safe threshold clearance and gear touchdown at least 1,000 feet down the runway.
Also:
FCTM:
When visual contact with the runway is established, maintain the glide path to the flare. Do not descend below the glide path.

[rudderrudderrat]

Hi Jwscud,
He felt I was "high", despite me touching down abeam the PAPIs.
There are a couple of reasons your captain might have said that:
1) Airbus visual illusion awareness (http://www.airbus.com/fileadmin/media_gallery/files/safety_library_items/AirbusSafetyLib_-FLT_OPS-HUM_PER-SEQ11.pdf), page 6 "An uphill slope creates an illusion of being too high (impression of a steep glide path);" or

2) He may of been mindful of the landing distance available. e.g. If you look at CDG RW27L (http://www.blackholes.org.uk/PP/CDG.pdf) Difference between RWY 27L LDA (3,600m) and Distance beyond Glide Slope (3,256) = 344m. If you needed that extra 44m landing distance, due to aircraft performance, then you would have to plan to cross the landing threshold at 50 feet.

[cosmo kramer]

If you look at LGW 26L / 08R, LGWrunway there are two landing distances published for each runway. They depend on whether you follow the glide path to touch down, or deliberately fly below the glide path to cross the landing thresh hold at 50 feet on a 3 degree profile.
Long ago since using Jeppesen. Are you sure about this? A reference would be nice.

As far as I remember "beyond the glide slope", is simply a measurement of the distance from the glide slope antenna to the runway end. Which fit very well with the the antenna, in your example, is almost exactly 1000 feet down the runway or 50 feet crossing altitude of the threshold, being on the 3 deg glide slope.

[rudderrudderrat]

Hi cosmo kramer,

Please see https://www.vnv.nl/commissiepub/4450
"As discussed previously manufacturer data is normally based on a threshold crossing height of 50 ft and a touchdown point that may not be achievable in line operations."

The picture shows the increased Landing Distance by being 100 ft over the threshold = 300m.

All of our performance data is based on LDA (i.e. assumed from being 50 ft above the landing threshold.)
Please See Alicante ALC (http://www.blackholes.org.uk/PP/ALC.pdf) Difference between RWY 10 LDA (3,000m) and Distance beyond Glide Slope (2,650m) = 350m.
& CDG CDG (http://www.blackholes.org.uk/PP/CDG.pdf) Difference between RWY 27L LDA (3,600m) and Distance beyond Glide Slope (3,256) = 344m.
& Madrid MAD (http://www.blackholes.org.uk/PP/MADLDA.pdf) Difference between RWY 32R LDA (3,000m) and Distance beyond Glide Slope (2,722m) = 278m.

It would be interesting to learn from the OP what the difference in the published "LDA" and "Distance beyond the Glide Slope" was for his 2,000m airport.

[cosmo kramer]

It's NOT a correct calculation you are using:

50 feet height = 1000 feet or 300 meter
100 feet height = 2000 feet, 600 meter or 0.3 nm.

All in round numbers of course.

Height (feet) = tan(glide path angle) x distance (has to be same unit, feet too).

Unless you can provide a reference FROM JEPPESEN (don't have Jeppesen available to look it up), I'll maintain that "Beyond the glide slope", is just a measurement of the distance from the antenna to the end of the runway (landing roll available, so to speak).

"As discussed previously manufacturer data is normally based on a threshold crossing height of 50 ft and a touchdown point that may not be achievable in line operations."
Normally = unsloped (flat) runway. And 3 degs glide slope. Steeper glide and upslope you pass the threshold higher, but still touchdown 300 meter down the runway (assuming no flare). Touchdown point decides your landing distance, not threshold crossing height.

[cosmo kramer]

All those airports you mention are completely normal 50 feet crossing height (on the glide, give or take a few feet). Seriously, I'm speechless if you are of this belief and practice this in daily ops!!!

The picture, I believe you are referring to, shows an EXTRA distance of 300 meter for crossing the threshold 50 feet too high (= 100 feet high, on a flat unsloped runway).
https://www.vnv.nl/files/img/landing.gif
50 feet crossing height = 300 meter to touchdown, 300 meter for flare = 600 meter.
100 feet crossing height = 600 meter to touchdown, 300 meter for flare = 900 meter = an extra 300 meter.

[rudderrudderrat]

Hi ,
I'll maintain that "Beyond the glide slope", is just a measurement of the distance from the antenna to the end of the runway (landing roll available, so to speak).
Correct.

Steeper glide and upslope you pass the threshold higher, but still touchdown 300 meter down the runway (assuming no flare).
Not so, other wise all the above quoted examples would have a difference of 300m between the published LDA and the "Beyond the glide slope difference".
Please see MRS.pdf (http://www.blackholes.org.uk/PP/MRS.pdf) for Runway 31R. The difference between LDA and "Beyond the glide slope" is only 262m. (Due crossing the threshold at 50 feet but on 4 deg glide slope)

There is a spread from 262m (MRS 31R) to 344m (CDG 27L) of 82m.
The point I am trying to make (unsuccessfully it appears) is that our performance calculations are based on LDA, but the "landing roll available" (for braking etc.) can differ by around 82m from the LDAs published for different Runways.

[PEI_3721]

cosmo, rudderrat, the simple position ‘beyond the glideslope’ may not be that easy; the ILS GS normally involves a reflected beam off the ground some distance in front of the antenna. This distance may vary with antenna/beam type, height, and offset.

[cosmo kramer]

In my opinion it's all extremely theoretical what you say, borderline gibberish.
The point I am trying to make (unsuccessfully it appears) is that our performance calculations are based on LDA, but the "landing roll available" (for braking etc.) can differ by around 82m from the LDAs published for different Runways."Beyond the glide slope" (from memory) is just an information to you where the glide slope antenna is placed. Nothing more and nothing less. Someone with a Jeppesen may provide an exact definition. Nothing to do with LDA or LRA.

I agree there is a variation of a few meters, where the glideslope antenna is placed. It probably has to do with obstruction areas, aircraft categories and type expected to use the approach etc. Anyway, 344 meter equals a height above threshold of 59 feet (assuming 3 degs glide). Tell me how much do you need to go below the glide slope (dots) to be 9 feet lower 344 meters from the antenna? But more important: Who even flies the glide at that height? You should be looking at the big white squares on the runway (aim point markings).

I agree that if making an auto land, the aircraft may be 9 feet too high in CDG (3600 meter runway). In my EFB there is a selection for auto land which will cause an additive to the LDR, probably to cover such minor discrepancies and system performance.
Further, if your performance calculations to another airport are that tight, that 82 meters means the difference of going of the runway or not, maybe you should consider a diversion (lousy visibility and 82 meter margin at max braking is not a cocktail I would recommend, even if factored).

Anyway it has nothing to do with the point or what the poster was asking. If there is an upslope in the touchdown zone it normal to pass the threshold higher than 50 feet. I.e. if threshold is at 230 feet and touchdown at 240 feet, passing over the threshold at 60 feet is normal, and does not affect your landing calculations (because you are touching down on the runway where you are supposed to).

[Gysbreght]

Touchdown point decides your landing distance, not threshold crossing height.To a first approximation (no flare) that is correct (*). However, the flare will take the airplane above the glide path, and the touchdown point will be beyond the aiming point. How much depends on the length of the flare. For a given amount of "gee" in the flare arc, the length of the flare increases with the change of rate-of-descent (relative to the runway surface) between the start of the flare and touchdown, i.e. with the angle between the glide path and the runway.

The AFM landing distance is measured from "a point 50 ft above the landing surface" for standard temperature. It is corrected for altitude and wind, but not for runway slope so it is sufficiently conservative for uphill sloping runways to absorb some increase of the flare distance.

Therefore the pilot of the OP did nothing wrong, and the captain had no reason to reprimand him or to call for a go-around. But suppose the captain said something like: "Look here, your landing was good, but it would have been even better if you had managed to cross the threshold below 50 ft" - would you disagree with him?

For downhill sloping runways the AFM landing distance is unconservative. Would it be wrong to use a glide path angle of -4 degrees when approaching a runway with 1.7% downslope?

(*) You seem to refer to 'touchdown point' when you really mean 'aiming point', i.e. the rectangular runway markings at the intersection of the glide path and the runway.

[cosmo kramer]

But suppose the captain said something like: "Look here, your landing was good, but it would have been even better if you had managed to cross the threshold below 50 ft" - would you disagree with him?
If you are asking me, then yes I would disagree. First, you are eating away on one margin (obstacle clearance), to increase another that needs no increasing (landing distance). Second, you change your profile in the last seconds of the approach, which may lead up to a long flare = nothing gained.

Boeing directly advices against doing so, as quoted earlier:
FCTM:
When visual contact with the runway is established, maintain the glide path to the flare. Do not descend below the glide path.

For downhill sloping runways the AFM landing distance is unconservative. Would it be wrong to use a glide path angle of -4 degrees when approaching a runway with 1.7% downslope?
Any slope affecting the ground roll would need to have appropriate corrections applied to the total LDR. A slope in prior to the touchdown point (normally upslope) doesn't affect the LDR, as the aircraft still doesn't have contact with the runway - pretty logical I'd say.

[Kefuddle]

Therefore the pilot of the OP did nothing wrong, and the captain had no reason to reprimand him or to call for a go-around. But suppose the captain said something like: "Look here, your landing was good, but it would have been even better if you had managed to cross the threshold below 50 ft" - would you disagree with him?
I would heartily disagree with him. A 3 degree glide path to a 1% upslope would be 70' above the threshold for a 1,000' aiming point. If you try and make 50' over the threshold I reckon the only practical option is to increase the RoD of descent below 200' which isn't really buying into the spirit of a stabilized approach.

[Gysbreght]

If I may ask yet another ignorant question - if there is a PAPI/VASIS on a downsloping runway, would it be located 1000 ft from the threshold, pointing up at 3 degrees to the horizon, thus providing less than 50 ft threshold crossing height?

[Kefuddle]

There certainly seems to be some airfields with threshold crossing altitudes below 50'. As far as I can determine according to Annex 14, the maximum slope in the first 25% of the runway (essentially the touchdown zone) is 0.8%. This could mean a threshold height of as little as 30' for a 3 degree slope, which seems a bit extreme. This also makes the maximum crossing alt 66', so disregard the 1% example!!

However, from what I can determine the design of a non-precision approach, the glidepath is worked back from 50' above the threshold, so threshold crossing heights other than 50' seem to apply only to precision approaches.

[rudderrudderrat]

Hi Gysbreght,

if there is a PAPI/VASIS on a downsloping runway, would it be located 1000 ft from the threshold, pointing up at 3 degrees to the horizon, thus providing less than 50 ft threshold crossing height?
If you look at the ALC link I posted #23, the runway has a down slope of 98 feet in 3,000m (1%). The ILS glide slope transmitter is located 350m from runway threshold (difference between LDA (3,000m) and "distance beyond glide slope" (2,650m)).

The 3 deg glide slope would be 18.3m (60 feet) above the threshold on a level runway. Alicante's runway threshold is 11 feet higher than the glide slope transmitter, so the threshold crossing height is 49 feet.

The published LDA (no inset landing threshold) is 3,000 m, but the effective landing distance is 50m shorter (due to the down slope).
The converse would be true if you landed on the reciprocal runway and crossed the threshold at 50 feet.

Maybe that was the point the OP's Captain was trying to make?

[Gysbreght]

Hi rudderrudderrat,

Thanks for your reply which was most helpful. In your ALC example the treshold height of 50 ft and the glideslope of 3 degrees result in the glideslope/runway intersection being further from the threshold on a downslope runway.

The converse would be true if you landed on the reciprocal runway and crossed the threshold at 50 feet.
That's logical, isn't it? Therefore it is perhaps worth repeating: It would be interesting to learn from the OP what the difference in the published "LDA" and "Distance beyond the Glide Slope" was for his 2,000m airport.

[Jwscud]

Runway length 2004m

Beyond GS 1704m.

The ILS is also of poor quality, meaning the glide slope is untrustworthy below around 500' afe and does not keep you on a straight 3° path but shallows then steepens slightly which does not help a stable approach if you are following the GP.

[rudderrudderrat]

Hi Jwscud,

This is a link to an accident report of a TriStar which ran off the end of Leeds Bradford airport. http://www.aaib.gov.uk/cms_resources.cfm?file=/2-1987%20G-BBAI.pdf

Landing distance calculations is not an exact science (too many variables) so there is a big scatter in achieved results. Sometime you may wish you had that extra 50 m of runway in front of you rather than behind you.

Please would you tell us which was the airport in post#1?

[Gysbreght]

Hi rudderrudderrat,

thanks for the link to an interesting report. I think the following (from para. 1.10.4 of the report) is relevant to our discussion:
The relevant CAA recommendation was that PAPIs should be sited to give a wheel height over the landing threshold of 30 feet for the most demanding aircraft that used the aerodrome.It would be of interest to know if that recommendation is still valid and also what practices apply in other parts of the world. Questions with regard to the OP:
a. How does the eye-to-wheel height of the OP's aircraft compare to the "most demanding aircraft that use(s) the aerodrome"?
b. Are pilots expected to make adjustment for their eye-to-wheel height when using PAPIs?

[cosmo kramer]

Landing distance calculations is not an exact science (too many variables) so there is a big scatter in achieved results. Sometime you may wish you had that extra 50 m of runway in front of you rather than behind you.
I wholeheartedly disagree.

One thing is the dispatch criteria, where the distance is factored with 1.67 (dry), 1.92 (wet) or for contaminated highest of 1.15 x actual contaminated of wet, which ever is higher. A 50 meter margin may be ok, since you already have a margin in the calculations (but be careful with wet contaminants, as they will generally be limited by 1.15 and thus have the lowest margin).

If your inflight calculations (ACTUAL unfactored landing distance) are so tight, that you believe you need to do "tricks" to obtain an extra 50 meter, and if you did a calculation for dispatch and it was ok, the only possible explanation that your inflight calculations may show such a discrepancy, is that during the flight the runway unexpectedly became contaminated/wet (and was not forecasted for you to consider during dispatch). In that case I would either recommend to hold for the runway to be cleared or a diversion. If your company choses to operate into such a short runway, for the type you are flying, I am sure they also accepted the higher risk of diversions in such cases.

[cosmo kramer]

...and as a note to the above. Obviously you wouldn't dispatch to a runway expecting it to be contaminated. You would expect it to be cleared and wet, when arriving. And bring the necessary extra fuel, to be able to hold waiting for it to be cleared (if possible), or divert.

[safetypee]

cos, et al, the dispatch requirements provide a margin in dry and perhaps a lesser extent in wet conditions, but it is important to understand what these involve – EU OPS 1.515 / 520. Note the assumptions, including slope, which is one reason why a prelanding check (calculation) is required (1.400).

The dispatch calculation for wet/contaminated, and contaminated runways do not have the same margins as above; they may be significantly less, thus the required level of safety has to be balanced by infrequent use and/or additional training/procedure CS 25 AMC 1591 para 8.8.1:-
“Operation on runways contaminated with water, slush, snow, ice or other contaminants implies uncertainties with regard to runway friction and contaminant drag and therefore to the achievable performance and control of the aeroplane during take-off, since the actual conditions may not completely match the assumptions on which the performance information is based. Where possible, every effort should be made to ensure that the runway surface is cleared of any significant contamination.”
i.e. clear the runway or avoid contamination wherever possible. :ok:

Actual landing distances are ‘tight’; I agree, also that many of the actual landing distances published even with +15% are unrealistic and may not provide sufficient safety margin for a range of conditions including THC / runway slope
TCH is referred to in 1.410, but does not give any values – only safety. Thus the issue is to assess the many parameters (as in this thread) to define what is acceptably safe – something which the crew has to judge at the time, but hopefully with published operational advice / guidance.

Re the OP (and some discussions), 50ft is the reference for establishing certificated performance, but it's not 'a limit' in operation, EU OPS provides guidance how this is to be applied, thus on an upsloping runway the landing should consider factors which will maintain the required level of safety, e.g. a maximum for the higher TCH, more restrictive TCH airspeed, wind limits – particularly tailwind, a limit of acceptable touchdown zone adjusted for runway condition, braking to be used, and for the operator the condition of the overrun area.
The OP ‘Captains’ view could have been expressed as an issue for learning/discussion, but if it was “I am right your are wrong”, then it would be better to jointly explore the details of landing performance, particularly the assumptions and judgements required by the lack of hard numbers which we all like to rely on.