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Wake enroute

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Wake enroute

Old 14th Nov 2018, 22:33
  #21 (permalink)  
 
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What is it about Chally's and A380's? I'm another with such "experience", not extreme but very exceptional, 2k below, crossing about 12 behind ( so basically about a minute 30 secs) A Malay machine, not that that makes any difference. I've never heard of the "A380 warning" either & as the previous poster alludes to, either the seperation standard is good enough or it isn't. Too much "politics" from ATC now, but perhaps thats a new topic!
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Old 15th Nov 2018, 04:48
  #22 (permalink)  
 
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Originally Posted by Knold View Post
I find it utterly bizarre that this is not part of a certification process for a new aircraft. It should be up to Airbus when designing the monstrosity to study how badly it will effect other traffic.
Ah, but airbus DID study this. I'm sure there must be info available on it publicly, it's quite an interesting piece of work. airbus link heer for starters ...

Basically, when the 380 was first being brought into service, there were fears expressed that it might have an excessive wake, and various ideas were mooted in terms of an extra-special category for it, extra long separation criteria, etc. All things airbus wanted to avoid if they could justify that, based on actual data rather than a general "its a monster lets treat it like one" reaction.

So they set up a series of wake encounters using a single-aisle as the 'target', various different large aircraft (not just the 380, they wanted to see the behaviour in context) as the generators, plus some other research aircraft gathering data. What they found indicated that the 380 isn't a 'monster' and resulted in the separation criteria we have today. They also had some interesting findings on what the best (and worst) response was by a target finding itself being "waked".
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Old 15th Nov 2018, 08:21
  #23 (permalink)  
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Thanks Mad (flt) Scientist. Interesting stuff.
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Old 15th Nov 2018, 10:20
  #24 (permalink)  
 
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The scientific approach to determining wake strength used for the A380 has been applied across the spectrum, hence the RECAT-US and RECAT-EU schemes, and the forthcoming Static Pair Wise Separation.

I'd rather use a wake scheme based on science than the ICAO 'finger in the air' categories and separations that most of the world still use.
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Old 15th Nov 2018, 10:35
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Just to be clear: is it being stated or claimed here – by those who are experienced in the game – that en route wake from a "super" A380 is worse, more to be avoided, than wake from a large "heavy" such as a 747-8 or a 787? The "beast of a wake" that underfire posted at #9 was from a 787.

Gonzo, can you briefly explain (for benefit of this small-aircraft pilot) about the forthcoming Static Pair Wise Separation?

Last edited by OldLurker; 15th Nov 2018 at 10:50.
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Old 15th Nov 2018, 16:40
  #26 (permalink)  
 
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Review the FDR data. Itís in the web. Some, and perhaps a lot, of the damage came from poor recovery inputs by the pilot(s).
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Old 15th Nov 2018, 16:49
  #27 (permalink)  
 
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Approx 15-25 nm in trail is the risk area. Inside of 15 nm it would need to desecebd at 500 FPM to be 1000Ē lower. After 25 nm youíre outside of three minutes.

The wake isn't visible. Absent a significant wind shift contrails will give you a good indication of where the wake is.

Wake is a function of weight, wingspan, and AOA. All the larger twins have wingspans in the 210í (65 m) range. And it drops 1000í. Been there done that. Moderate turbulence in a 777 behind a 747-400 at cruise.
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Old 15th Nov 2018, 18:27
  #28 (permalink)  
 
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I have been warned about crossing behind and below the A380 a few times in European airspace.
I have been vectored in order to get further away from it, and I have been asked to climb 1000 ft to get above the wake. We were to heavy but the controller was happy to let us climb two hundred feet and then return to our cleared altitude after we passed the A380 track.
Not sure if the controllers have to do any active separation, but I don’t mind if they do. I fly 737.
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Old 16th Nov 2018, 01:48
  #29 (permalink)  
 
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The scientific approach to determining wake strength used for the A380 has been applied across the spectrum, hence the RECAT-US and RECAT-EU schemes, and the forthcoming Static Pair Wise Separation.

I'd rather use a wake scheme based on science than the ICAO 'finger in the air' categories and separations that most of the world still use.
I would not hold you breath, there is actually very little actual science in RECAT. RECAT is good for final approach segment, and perhaps the departure recat will come alive again.
The entire RECAT was based on 4 valid wake measurements out of Memphis....What has been known for years is that the wakes dont last as long as they state, and especially in even a light crosswinds, are out of the flightpath in around 20 seconds.
So the 'science' is just closing up the spacing until you have more wake encounters, then they will back it off. It does not take into account still air, or inversion layers, in reality, it is just sticking their finger up somewhere.(this is why they are studying 'acceptable' wake encounters.

Look at LHR. Doesnt everyone think there is a good possiblity of a wake encounter on final, and expect a wake encounter on dep? The reason there are not more serious incidents is that everyone expects it to happen.

The "beast of a wake" that underfire posted at #9 was from a 787.
Yes, the post was about how severe the wake is from the 787.

The 748 was required to do studies on wake as well as part of cert.
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Old 16th Nov 2018, 03:29
  #30 (permalink)  
 
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As the wake descends you shouldn’t encounter it when descending down the glideslope, notwithstanding aircraft that may be intercepting at a different altitudes.
Almost guaranteed as you approach the runway as the wake hits the ground and bounces back up. The last place you want an encounter!
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Old 16th Nov 2018, 04:23
  #31 (permalink)  
 
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Old 17th Nov 2018, 10:03
  #32 (permalink)  
 
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the first EASA link was published after the incident actually.

Interestingly enough, SLOP was not permitted on that route during the time of the incident...

https://www.flightglobal.com/news/ar...on-rou-437303/

ATCO’s in that area often warn me of the proximity of Super’s.
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Old 17th Nov 2018, 15:38
  #33 (permalink)  
 
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As the wake descends you shouldn’t encounter it when descending down the glideslope, notwithstanding aircraft that may be intercepting at a different altitudes.
The wake will also hang on inversion layers
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Old 21st Nov 2018, 02:38
  #34 (permalink)  
 
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Originally Posted by underfire View Post
I would not hold you breath, there is actually very little actual science in RECAT. RECAT is good for final approach segment, and perhaps the departure recat will come alive again.
The entire RECAT was based on 4 valid wake measurements out of Memphis....What has been known for years is that the wakes dont last as long as they state, and especially in even a light crosswinds, are out of the flightpath in around 20 seconds.
So the 'science' is just closing up the spacing until you have more wake encounters, then they will back it off. It does not take into account still air, or inversion layers, in reality, it is just sticking their finger up somewhere.(this is why they are studying 'acceptable' wake encounters.

Look at LHR. Doesnt everyone think there is a good possiblity of a wake encounter on final, and expect a wake encounter on dep? The reason there are not more serious incidents is that everyone expects it to happen.


Yes, the post was about how severe the wake is from the 787.

The 748 was required to do studies on wake as well as part of cert.
Are you talking about RECAT in the USA, or RECAT-EU which is different? And yes, RECAT-EU is only applied for intermediate and final approach spacing, and departure spacing at LHR. RECAT-EU is certainly based on far more measurements than just 4.

How does an encounter become less serious if the following flight crew expect it?

From most of the main LHR-based airlines we can get access to FDR data, from which one can extrapolate the force of the wake.
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Old 21st Nov 2018, 02:41
  #35 (permalink)  
 
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Originally Posted by OldLurker View Post
Just to be clear: is it being stated or claimed here Ė by those who are experienced in the game Ė that en route wake from a "super" A380 is worse, more to be avoided, than wake from a large "heavy" such as a 747-8 or a 787? The "beast of a wake" that underfire posted at #9 was from a 787.

Gonzo, can you briefly explain (for benefit of this small-aircraft pilot) about the forthcoming Static Pair Wise Separation?
Yes, instead of having a separation matrix of 4x4 categories, or 6x6 categories, you have a matrix of 96x96 aircraft types, where, depending upon your desired resolution (0.1nm, 0.25nm, 10sec, 20secs etc) each aircraft pairing can have its own separation.

For example, 747-400 followed by A320 might be 3.2nm, 747-400 followed by A319 might be 3.4nm, 747-400 followed by A321 might be 3.1nm. And so on......
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Old 21st Nov 2018, 14:29
  #36 (permalink)  
 
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I dont think the 96x96 will ever be used. ATC certainly wont figure that out. Currently working with Thales to add the separation matrix to the ATC system. This will work with the flow manager for arrival, and the departure manager. The system will adjust the flow manager to affect the frequency of the arrival based on wake conditions.This will work abck through the system to enroute.
On the screen, there are 2 features, a moving dot on the approach path for intercept target, and a cone behind each ac for the min wake separation. Interesting that US based the cone is one way and it is opposite for ICAO based, go figure.

How does an encounter become less serious if the following flight crew expect it?
When the crew is ready for it, the adventure is much less of an adventure. Higher thrust setting and according flap setting. LHR is a natural example with the ARR speeds higher than most. I feel that this at least minimizes the wake effect.

Interestingly enough, on Sunday, DEP from SEA, in A321, hit a hell of a wake at about 300 AGL. just after rotate, rolled left then right, bouncing the whole way.. about 2 mins behind A320 sharklet. Ac was all over the place.

Currently looking at a more refined definition of simply wingspan/weight, using wing loading, as I have seen very strong wakes from smaller ac. I am looking at weight and wing area, (not simply wingspan) and wing shape. As noted before, as an example, the variable upswept geometry of an ac like the 787...
As examples: Wing area loading
A380: MTOW/845 sq m is 680 kg/ sq m
B747: MTOW / 511 sq m is 652 kg/sq m
B789: MTOW/360 sq m is 705 kg/sq m
B757: MTOW/376 sq m is 678 kg/sq m

Last edited by underfire; 21st Nov 2018 at 14:43.
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Old 21st Nov 2018, 22:34
  #37 (permalink)  
 
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Originally Posted by underfire View Post
I dont think the 96x96 will ever be used. ATC certainly wont figure that out. Currently working with Thales to add the separation matrix to the ATC system. This will work with the flow manager for arrival, and the departure manager. The system will adjust the flow manager to affect the frequency of the arrival based on wake conditions.This will work abck through the system to enroute.
On the screen, there are 2 features, a moving dot on the approach path for intercept target, and a cone behind each ac for the min wake separation. Interesting that US based the cone is one way and it is opposite for ICAO based, go figure.


When the crew is ready for it, the adventure is much less of an adventure. Higher thrust setting and according flap setting. LHR is a natural example with the ARR speeds higher than most. I feel that this at least minimizes the wake effect.

Interestingly enough, on Sunday, DEP from SEA, in A321, hit a hell of a wake at about 300 AGL. just after rotate, rolled left then right, bouncing the whole way.. about 2 mins behind A320 sharklet. Ac was all over the place.

Currently looking at a more refined definition of simply wingspan/weight, using wing loading, as I have seen very strong wakes from smaller ac. I am looking at weight and wing area, (not simply wingspan) and wing shape. As noted before, as an example, the variable upswept geometry of an ac like the 787...
As examples: Wing area loading
A380: MTOW/845 sq m is 680 kg/ sq m
B747: MTOW / 511 sq m is 652 kg/sq m
B789: MTOW/360 sq m is 705 kg/sq m
B757: MTOW/376 sq m is 678 kg/sq m
Of course 96x96 will be used. Itís coming to LHR in the next few years.

Expectation might mean that correction is quicker and therefore requires less roll input, but the initial roll moment will still occur. Thatís what is measured.

LHR arrival speed is higher? Relative to what? 160kts to 4DME is not high in my opinion. For some of our types thatís too slow


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Old 22nd Nov 2018, 13:00
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Originally Posted by Gonzo View Post


Of course 96x96 will be used. Itís coming to LHR in the next few years.

Expectation might mean that correction is quicker and therefore requires less roll input, but the initial roll moment will still occur. Thatís what is measured.

LHR arrival speed is higher? Relative to what? 160kts to 4DME is not high in my opinion. For some of our types thatís too slow


It can be tough to be stabilized at 160/4 DME on some flights.
For what types is 160 kts too slow?
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Old 22nd Nov 2018, 13:22
  #39 (permalink)  
 
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As examples: Wing area loading
A380: MTOW/845 sq m is 680 kg/ sq m
B747: MTOW / 511 sq m is 652 kg/sq m
B789: MTOW/360 sq m is 705 kg/sq m
B757: MTOW/376 sq m is 678 kg/sq m[/QUOTE]

Using Wikipedia as a source produced slightly different numbers -

A380 - 680/sq m
748 - 808/sq m
744 - 786/sq m
773 - 700 kg/sq m
789 - 674/sq m
763 - 660/sq m
752 - 624/sq m

Interesting that the 747 numbers are much higher than the others. Perhaps a mistake in wikiís data?
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Old 22nd Nov 2018, 14:49
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Not sure which wiki data you are referencing.
https://en.wikipedia.org/wiki/Wing_loading
https://en.wikipedia.org/wiki/Boeing_747-8


I did not use wiki data, that is not vetted and really should not be relied on.

Luftansa uses 511 sq m for 744 and 554 sq m for 748, I did not use 748 data as there are very few of these in service.
For the 787 series, there is a scientific paper on this aircraft.
A388 was from Airbus.
B773 was from Swiss Air. (427 sq m)

BTW, Airbus uses the center wing in their area calculations, Boeing does not. This may be why you will see such differences in similar ac, or why there are differences in the source on same ac.

This website seems to be a bit more accurate: http://www.flugzeuginfo.net/acdata_en.php

Of course 96x96 will be used. It’s coming to LHR in the next few years.
I sincerely doubt this. I cannot see ATC sorting this many variants out, especially of the same ac variants. Aside from that, by the time this ill-fated scenario rolls out, there will be even more variants. (now it is a 115 by 115 matrix)
There is the potential to have something similar, if NATS gets the automation worked out on the new ATC system, but this would require the new system...lets see how that works out, and in how many years.

Interesting to note the RECAT pilot program at Memphis, no increase in REPORTED wake encounters...(no decrease either) I know every pilot reports every wake encounter, so it appears that RECAT works, right?

Curious, what is going on with time based separation at LHR?

160 at 4DME is fast. For the 320 and 737 variants, not an issue., but try to manage the energy of a large aircraft from 160 down to FAS from 4 DME. (and with steeper approaches?!?!) Most large ac the optimum GPA is 2.8 to manage the energy.

Last edited by underfire; 22nd Nov 2018 at 16:12.
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