Landing Performance on a sloping Runway
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Landing Performance on a sloping Runway
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.
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.
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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.
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.
Last edited by JammedStab; 7th May 2014 at 23:29.
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Its not rocket science
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.
Last edited by ZAZ; 7th May 2014 at 19:47.
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.
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.
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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.
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.
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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.
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.
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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.
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.
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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.
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.
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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.
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.
Last edited by Gysbreght; 9th May 2014 at 10:56. Reason: P.S. 1&2
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Well, having actually done extreme gradient ops, I can tell you that's not the way it's done.
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.
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.
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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.
(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.
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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.
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.
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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):
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.
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.
Last edited by Gysbreght; 11th May 2014 at 11:12.
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Quote Jwscud:
I would welcome opinions and references as it is an area I could do to improve my knowledge on.
I would welcome opinions and references as it is an area I could do to improve my knowledge on.
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.
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.
FCTM:
When visual contact with the runway is established, maintain the glide path to the flare. Do not descend below the glide path.
When visual contact with the runway is established, maintain the glide path to the flare. Do not descend below the glide path.