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Landing distance available

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Landing distance available

Old 21st Oct 2012, 12:21
  #21 (permalink)  
BBK
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Talking

I asked the original question as I couldn't find the definitions in the Jepps and and haven't seen my perf A notes in years! Some interesting comments and info so thanks to all of you for your input. Since I started the thread I've done some more reading up and the link to the Dutch study was particularly interesting.

The QRH on the 744 has a note that states the assumption are 50 ft above the threshold and approximately 1000 ft flare distance. in that sense the 'glide slope distance' will be conservative by about 1000 ft so over cautious perhaps. Quite why Jepps do not always provide a threshold distance eg LHR 27L I still cannot determine - especially as the geometry appears identical to 27R.

What is/has always been obvious is that the data in a QRH/performance manual derived from a company test pilot flying said type may not be achievable on the line so maybe some healthy factoring is prudent. For example, using the above example a senior trainer mentioned that he believed Boeing were due to revise the tables and up the flare distance to about 1500 feet. I did notice that value (1500) mentioned in the DLR report.

Anyway, it's been a useful exercise for me to reacquaint myself with the assumptions used in the performance data. Now of course if we begin to look into landing on contaminated runways all bets are off. Best advice given to me is don't! Happy landings.

regards

BBK
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Old 21st Oct 2012, 12:48
  #22 (permalink)  
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No, but regardless of where they are situated, they are required to deliver you on the correct glide slope to a point 15 to 18 m above the threshold (some caveats apply, but that's the gist of it).
No they don't. clearly if you look at the RWY layout for a precision and NON precision approach you might have noticed that the TD point on the RWY with ILS or PAR will be co-located with imaginary GS intercept point with the RWY and PAPI or VASI will be located just abeam whereas on the RWY laid out for NON precision approach TD point or aiming point will be 1000 ft mark behind the THR. That's the background of 2 different distances. Conclusion: ILS or PAR equipped RWY will have it's aiming point located further into RWY thus reducing LDA. As mentioned by BKK it could be up to 1500 ft. In case of HNL 08L it's 12300-11066=1234 ft.

As for your questions: Definition of landing beyond the GS is given in Jeppesen section airport chart legend under number 6 there's also LAHSO definition. LDA is translated as actual landing distance used by airbus in other words it's the one used for certification. You can read advisory circular from FAA regarding this topic here http://flightsafety.org/files/RERR/A...20Overruns.pdf
and regarding LAHSO here Land and Hold Short Operations (LAHSO) in particular talking bout TCH. Good luck.
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Old 21st Oct 2012, 12:54
  #23 (permalink)  
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Has anyone found a definition for "distance beyond the G/S"? Is it beyond the GP mast, beyond point R... for starters? If there's no definition, the figure is utterly useless IMNSHO. The two definitions I mentioned can differ significantly, and you could probably invent a fair few more.
From the Jepp :

Landing Beyond

Threshold - When the landing length is restricted, the length shown is the distance beyond the landing threshold to the roll out end of the runway.

Glide Slope - The length shown for ILS is the distance from a point abeam the glide slope transmitter to the roll-out end of the runway. For PAR, the length shown is the distance from the theoretical glide slope interception with the runway to the rollout end of the runway. If both ILS and PAR are available, data provided is for ILS.

And since "LANDING DISTANCE"

The landing distance represents the distance from the 50 ft height point to complete stop on a smooth, dry, hard-surfaced runway. [...] (AFM definition)

In my opinion we consider the Landing beyond threshold as our reference distance or, if it is not available (no displaced threshold) we consider the usable runway length depicted on the chart itself.

What do you think ?
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Old 21st Oct 2012, 13:44
  #24 (permalink)  
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If you read Annex 14, you will find that the distances to the aim point and TDZ markings depend on runway length/LDA and not on the approach type. I'm guessing the source of the confusion is the fact that you'll be more likely to see NPAs to short runways.

The runway markings will not coincide with the GP beam runway interception point. I would assume this to be based on the assumption of longer runways mainly being served by larger aircraft, with larger separation between GS antennas, pilot eye points and wheels.

The VASI units will typically not be colocated with either. They'll be located such that the typical aircraft serving the runway will have on-path indications while on the GP. Shorter/smaller aircraft will see below path indications on short final. The aim point markings will be made to coincide with the VASI indications though.

However, this is irrelevant as it has nothing to do with the specifications for the ILS. The ILS beam will lead to a point 15-18 m above the threshold (with caveats). If it doesn't, the facility is not compliant with Annex 10 and will not be approved during commissioning. For CAT II/III, that's a requirement. For CAT I, 15-18 m is a recommendation, but "ensuring [...] safe and efficient use of the runway served" is a 'shall'.

The fact remains: The location of the GP mast is irrelevant. The GP will cross the threshold at 15-18 m, barring shoddy CAT I installations and short runways.

So ALD would be an FAA-ificiation of LDR, or is there a subtle difference? Don't really care to compare definitions at the moment. Yay, we can have the RNAV/PBN/RNP debacle all over again.

@I-2021,
thanks. That's a risky definition. The distance between the GP beam intersection with the runway and the point abeam the GP mast can vary significantly (think sideslope). Clearly, the former is what is of operational interest but yet they publish the latter. I wonder where Jepp got their definition though, if it is an internal product or if it is based on official guidance somewhere...

I agree with your conclusions regarding operational use, even though I wonder about the legality of the figure in the maps. I'd hit the official publications first to see if there's an LDA in there that Jepp omitted.
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Old 21st Oct 2012, 14:39
  #25 (permalink)  
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ft, Location
The aiming point marking shall commence no closer to the threshold than the distance indicated in the table below, except that on a runway equipped with a visual approach slope indicator system, the beginning of the marking shall be coincident with the visual approach slope origin. Where a touchdown zone marking is provided, the lateral spacing shall be the same as that of the aiming point marking.

Last edited by 9.G; 21st Oct 2012 at 14:40.
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Old 21st Oct 2012, 14:57
  #26 (permalink)  
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https://docs.google.com/viewer?url=h...%2Fa11-h06.pdf something to read about the changes of the runway markings equipped with precision instrument approach system implemented in down under.

Last edited by 9.G; 21st Oct 2012 at 14:58.
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Old 21st Oct 2012, 15:35
  #27 (permalink)  
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Yes, very good. Just what I wrote a few posts up.

Originally Posted by ft
The aim point markings will be made to coincide with the VASI indications though.
Note the word 'origin' in the text you quoted. The visual approach slope origin is not the same as the actual VASI unit.

And it is still irrelevant to the point I was making, so I conclude that we agree. On slope, visual and GP, you'll be at 15-18 m as you cross the threshold.

Last edited by ft; 21st Oct 2012 at 15:35.
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Old 21st Oct 2012, 16:46
  #28 (permalink)  
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not quite ft, one will cross the the threshold at the promulgated TCH, whichever that might be. in case of HNL 08L it's 80 ft. The question here is when should LDA beyond GS be used if at all? As we've learned there's a discrepancy between the certification data based on 50 ft TCH and promulgated TCH which in turn will be adjusted to coincide with the GS and VASI, aiming point. Bottom line is instead of touching down at 850 ft with 480 ft/min as assumed in AFM you'll fly the ILS till the CAT I minima then transition to visual aiming for the aiming point thus touching down at closer to the 1300 ft mark. That's about the figure corresponding to the LDA beyond GS. Therefore when your operational landing distance is smaller than beyond GS you're good to go. In the extreme case you could be within the threshold value but above GS one. I think all those publications have made it clear that certification isn't real life neither on the performance side nor on the installation one. Be wary of the odds might prove useful.
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Old 21st Oct 2012, 17:18
  #29 (permalink)  
 
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9.G said

Alright M2002, now tell me which distance do take in case there's only LDA beyond the GS published? Plenty of those around.
Well, as I-2021 said, according to Jepp, threshold distance is depicted only if it there is a restriction (displaced threshold and the like, I assume). So I will use the full distance shown in 10-9 in those cases where there is no restriction. Someone here also pointed out that in their OM it is specified to do it that way.

In any case, I can only compare performance calculated from 50 ft with LDA from the threshold (and again, still remains the question of those extra feet of the TCH above 50 ft?).

My FCOM, as most of FCOMs, gives me distances from 50 ft. Beyond glide slope distances are simply useless for me. Its like mixing K and C. They are the same but referred to different datums.

By the way, 9G, How do you calculate if your landing distance is OK for a given runway? What do you use?
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Old 21st Oct 2012, 17:38
  #30 (permalink)  
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to visualize the difference between the 2 values let's consider a practical example. DTM RWY 06. RWY physical length 6562 ft landing beyond the THR 5577 which is the same as TORA from B. LDA beyond the GS is 4454 ft. Needless to say the runway is limiting here. Let's assume you're conducting a CAT II approach with an auto land on RWY 06 dry, 0 wind on A 320 with 60 tons LW. Let's crunch the numbers: Autoland distance with configure full, auto brake MED is 1440 meters = 4724 ft. According to your thesis we're good to go coz we're well within 5577 whereas I say nope, can't do coz I'll be over my LDA beyond the GS by 270 ft. Interesting to hear other opinions.

Last edited by 9.G; 21st Oct 2012 at 17:41.
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Old 21st Oct 2012, 17:59
  #31 (permalink)  
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In any case, I can only compare performance calculated from 50 ft with LDA from the threshold (and again, still remains the question of those extra feet of the TCH above 50 ft?).
gimme one reason why you do that? LDA is the distance available for a ground run. So it all depends on where you touch down, logically. The differences between RLD-ALD used for certification and actual TD point on a ILS will vary for all the aforesaid reasons. TO tackle the issues both boeing and airbus came out with OPERATIONAL landing distances which are realistic and include margin. However that still doesn't mean you'll hit the tarmac on 850 ft mark, does it? Therefore when you fly an ILS approach you'll touch down further into the RWY up to 1500 ft in extreme case, depends on TCH. When ILS is flown operational landing distance must be equal or less to LDA beyond the GS. The difference between the THR and GS is usually 1000-1300 ft. In other words 1300 ft left behind are of no use to me. That's how I do it. Worthwhile to mention that LAHSO LDA is taken from the THR and can bite one in the arse.
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Old 21st Oct 2012, 20:42
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"ICAO SARPs define the term 'Landing Distance' as "the horizontal distance traversed by the aeroplane by the aeroplane from a point on the approach path at a selected height above the landing surface to the point on the landing surface at which the aeroplane comes to a complete stop" (ICAO Annex 8 Part IIIA Paragraph 2.2.3.3. and Part IIIB Sub-part B Paragraph B2.7 e)")
"LDA is the length of runway which is declared available by the appropriate authority and suitable for the ground run of an aeroplane landing"
EU OPS 1.480
Typically that selected height is 50 ft. Performance tables calculated by Airbus or Boeing or others provide landing distance performance based on those 50 ft, because that is supposed to be your height above the threshold (after an ILS, a PAR, a VOR approach or a visual circuit). That is why I want to know how many meters are there available from the threshold. Cause I can't work out what my ground run will be in my airplane. My FCOM just doesn't give me that information, nor any FCOM or POH I know of (which are just a few, I admit).

As it happens, for landing there is no such thing as clearway, nor stopway. All of the landing distance available must be a suitable for ground run surface even if you will sistematically overfly a significant part of it. A runway is suitable for a ground run from the very threshold, even before in case of displaced threshold. The threshold, displaced or not, is the beginning of the LDA. In fact, the Threshold is per se a declaration of the beginning of the LDA by the authority. It can be displaced forward, but not backwards. Airplanes don't touch down on the threshold, but still you need the runway to be suitable for ground run from the first inch of it. You can't flare before the runway threshold so you can "take credit" of as many meters before the aiming point (or shouldn't...).


I know that those values are based on tests made by test pilots who want to minimize landing distance as much as possible. That is why the FAA recommended adding a 15% to those values, if I recall correctly. But that is the best we have. I won't mind to use beyond glideslope distance if they give me landing roll distances, though

Jeppesen gives me the LDA in 10-9 in the airport plan view. If there is displaced threshold, LDA is given in the additional runway info, in 10-9 or in 10-9A. I have been looking at a few charts and what I-2021 said is correct: no displaced threshold, only beyond glide slope is given in the additonal rwy info. Displaced threshold, then you get the LDA.
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Old 22nd Oct 2012, 01:30
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Hate to add another complication, but the LDA is not shown on Jeppesen 10-9 charts. In the U.S., the LDA may be shorter than the runway length beyond the threshold if part of that runway length must be used to satisfy runway safety area, object free area, or runway protection zone requirements. See paragraph 4-3-6 of the AIM (http://www.faa.gov/air_traffic/publi...aim0403.html.6). At present, the only place declared distances are published in the U.S. is in the Airport/Facility Directory (Digital Airport/Facility Directory)

Last edited by donstim; 22nd Oct 2012 at 01:30.
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Old 22nd Oct 2012, 05:17
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Man, that's what we are saying.

Jepp specifies a threshold LDA only if the threshold is displaced, for whatever reason. If it is not, the full TORA as shown on the plan view of 10-9 is the LDA.

9.G

In that scenario of DTM rwy 06, you are good to go (if you have an emergency). If you haven't, you need to be able to land in the 60% of the runway.

Note:
It is worth taking a look at the link of the AIM. This paragraph clarifies the original question of this thread. The graphs are also useful.


Runway design standards may impose restrictions on the amount of runway available for use in takeoff and landing that are not apparent from the reported physical length of the runway or from runway markings and lighting. The runway elements of Runway Safety Area (RSA), Runway Object Free Area (ROFA), and Runway Protection Zone (RPZ) may reduce a runway's declared distances to less than the physical length of the runway at geographically constrained airports (See FIG 4-3-5). When considering the amount of runway available for use in takeoff or landing performance calculations, the declared distances published for a runway must always be used in lieu of the runway's physical length
.

conclusion: use TORA as the LDA unless tere is displaced threshold. Then a different declared LDA must be used. That is what Jepp does!

Last edited by Microburst2002; 22nd Oct 2012 at 05:30.
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Old 22nd Oct 2012, 08:37
  #35 (permalink)  
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M2002, let's exclude the emergency or contaminated RWY out of the equation, shall we? If we hit this path it ain't gonna be pretty, tell you that much. The scenario with DTM 06 is simple and straightforward question and the point I'm trying to make here isn't to be right but to raise the awareness of how inconsistent and unrealistic our perception is compared with the real world and commercial world. In the end it's your call however remember the desk flyers out there are quick to jump the gun to incriminate you. The bottom line is if you take THR and ALD as per AFM then you better fulfill all the assumptions it's based upon crossing the THR at 50 ft and not at the published TCH, smack that thing into the ground with 480 ft/min and slam those brakes like a mad man. Do we really do it in real life? Of course we don't. Regarding your last assumption let's consider you're going to LAX 24R what's your TORA on 24R and your LDA with TCH of 73ft? LAX - Los Angeles International Airport | SkyVector There's tons of supplementary data out there raising awareness of a mismatch between the manufacturer's data and the real world however airbus and boeing wanna sell those shiny new planes and we don't wanna put them in the ditch, do we? Good luck.
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Old 22nd Oct 2012, 09:17
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I've been following this discussion with interest, as I've never seen any information or calculations using distance from touchdown. All I get is the LDA (which may differ from the overall runway length) from the aerodrome charts and tables in the QRH (shortly to become an "app") with distances from 50' over the threshold. Factor as required.

Taking the example of LAX 24R, which by coincidence I landed a 777-300 on at MLW a week or two ago, my documentation reads:

TORA 2720m / 8925ft
LDA 2720m / 8925ft
3deg PAPI, MEHT 77ft

Now, not having any guidance material about MEHT and its implications, I had a root around and found a UK CAA document with this explanation:

8.5 The Minimum Eye Height over Threshold (MEHT), which is notified in AIP, is a reference value, calculated with respect to the promulgated approach angle for each PAPI. It is the lowest eye height over the runway threshold at which an on-slope indication will be seen. From examination of published MEHT, it may at first sight appear that for some runways, adequate wheel clearance at the threshold is not assured for all types of aircraft likely to use those runways. However, a typical eye height achieved in practice when crossing the threshold following well established 'on slope' approach would in fact be well above the published MEHT value.
From that, I infer that the figure of 77ft for LAX 24R (or indeed 73ft for LHR 27R) does not affect the LDR, so I can carry on as normal. Phew!
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Old 22nd Oct 2012, 09:30
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FW, MEHT is another cup of tea. Advisory Circular (AC) No. 302-009 - Transport Canada

P.S. that's a reason why airbus says PAPI below 200 ft is unreliable and not to be followed. Aiming point is your reference.

Last edited by 9.G; 22nd Oct 2012 at 09:34. Reason: adding p.s.
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Old 22nd Oct 2012, 09:58
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Yes, but I can't find a reference to TCH on any of the in-flight material I have access to, like charts, legends and performance data. In the Canadian doc. you linked to it just says TCH may vary between 40 and 60 feet and is normally 50 but to consult NAV CANADA for the exact value... Something I'm not likely to do on 5-mile finals.

Having done a bit of digging around, it seems that there is disagreement in heaven about what actually constitutes a "threshold" anyway.

Practically, as a humble airframe driver, I'd like to know whether the runway I'm about to land on is long enough, given the prevailing conditions and my state of urgency. All I have to go on is LDA from the charts and LDR from 50' from the manuals, as approved by the regulatory authority.

As an aside, if LAX has these non-standard higher-than-usual TCHs, how come they get CAT II & III on those runways when that's a long way outside Annex 10 regs...?
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Old 22nd Oct 2012, 13:23
  #39 (permalink)  
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Practically, as a humble airframe driver, I'd like to know whether the runway I'm about to land on is long enough, given the prevailing conditions and my state of urgency. All I have to go on is LDA from the charts and LDR from 50' from the manuals, as approved by the regulatory authority.
You're obviously a Boeing driver judging by the terminology used. Well, airbus came out with the LPC which includes a landing performance module. All those unresolved issues are tackled with this piece of wonderful software. It takes into account all the published data for the approach, landing and missed approach. TCH, manual landing or auto land and calculates operational landing distances. MEL can be included as well. There's your solution mate. No need to know all this crazy stuff. Just punch in the numbers and the screen either blinks in green GO or NO GO (emergency GO) in red. Nice, isn't it? Obviously not every operator wants to spend the cash on this tool but it pays off especially if RWY limited or contaminated combined with MEL.
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Old 22nd Oct 2012, 13:57
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As I mentioned earlier, looks like we'll get the equivalent Boeing Onboard Performance Tool (OPT) on EFB and/or iPad soon. At the moment, I just have to assume that all these little bits have been taken care of and rolled into our landing minima/maxima.

Mention TCH, MEHT, etc. to most line pilots and they'll give you a very blank look. Jeppesen appear to quote TCH, Navtech MEHT and Lido don't seem to think either worth noting from the charts I've seen...

OPT & LPC, UTC & TUC - everyone has to be different!
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