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Emirates B777 gear collapse @ DXB?

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Emirates B777 gear collapse @ DXB?

Old 30th Aug 2016, 12:27
  #1121 (permalink)  
 
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The 'big hangars' are immediately adjacent to where 521 came to rest...
Very true but surely of insignificance since that is where the aircraft came to rest which is the opposite end to where events unfolded. The actual wind closer to the 12L threshold is bound to be of more interest.

The wind speed given in the wind check with the landing clearance was 11 knots.
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Old 30th Aug 2016, 12:37
  #1122 (permalink)  
 
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immediately above the threshold of Runway 12L is the position at which the crew's problems regarding the go-around will have compounded.. From that position up to where the hull came to rest...which is the MAJORITY of the Runway, the aircraft is likely to have encountered changeable/adverse wind conditions (wind speed, wind direction, possible vertical windshear late in the approach/flare, and possibly building induced windshear)...
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Old 30th Aug 2016, 12:42
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How accurate is the 'reported wind' (Tower - landing clearance)?.. Where is that wind measured exactly...for aircraft landing on Runway 12L?... Did the 'reported wind' of 11 knots accurately represent the wind conditions at the time 521 initiated the flare?... Was the 11 knot wind an Average (mean wind) or was it a Gust?.. What averaging (time) period was used to calculate this landing wind speed/direction; was it a 3 sec / 10 sec / 1 min / 2 min or 10 min Wind?..

I'm not suggesting that other factors where not involved..such as possible incorrect GA technique, or the possibility of an unstable approach.. However, I do hope the investigation team are examining the impact of the local conditions at the time..

Last edited by Datum; 30th Aug 2016 at 13:11.
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Old 30th Aug 2016, 13:52
  #1124 (permalink)  
 
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Originally Posted by Datum View Post
The 'big hangars' are immediately adjacent to where 521 came to rest...

Has the airport/hangar infrastructure been wind tunnel tested, in order to ensure the preservation of safe operational margins in wind conditions such as those characteristic to flight 521?...
Presumably you mean to prevent or reduce mechanical turbulence? -you could ask yourself if "airport/hangar infrastructure" has been wind tunnel tested for this anywhere on earth; I think the answer will be no, no-one does this. Having trees and buildings near a runway is a fact of life for pilots.
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Old 30th Aug 2016, 17:58
  #1125 (permalink)  
 
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Datum, have you ever landed in Dubai, you are looking for smoking guns, where there are none. Mechanical turbulence caused by hangars, dream on
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Old 30th Aug 2016, 20:01
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Dangerous to be so confident you are correct without fully investigating and/or understanding what I'm suggesting.. The cost associated with wind tunnel testing is NEGLIGIBLE when compared to the cost of a Boeing 777 hull loss and the other costs directly/indirectly attributable to an accident!... As with most aviation mishaps, it is likely that MULTIPLE factors will have contributed..
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Old 30th Aug 2016, 20:58
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Has the airport/hangar infrastructure been wind tunnel tested ? Before they decide where runways and buildings should be in the next 40 years ? get real-
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Old 30th Aug 2016, 20:59
  #1128 (permalink)  
 
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If 10kts to 25kts of wind ends up with a smoking hull on the RWY, then Id suggest they're ATO will be doing some explaining. However combine that with the PF's apparent lack of real flying experience and it may be a different discussion. As for the temp and QNH, seriously.. a B773 on two engines at or under MLW .... please.

Im looking forward to reading (or at least anecdotally hearing) about the cockpit gradient/CRM issues with this event!

Hangers most def create mechanical turb. But usually only to the extent of an uncomfortable ride. Would have thought being their home port they'd have considered this.
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Old 30th Aug 2016, 21:31
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Datum, winds reported are at 10m AGL, so other than "windshear' there is no other reporting (currently) of the level of the windshear or the defining change.
When a pilot tells ATC they encountered windshear, usually as the reason for a GA, ATC broadcasts that until someone says they did not encounter windshear. In reporting winds, the 2min average based on 1 min readings is what is reported. Gusts are on a 10min average, unless the gust exceeds the average, then 5 minutes is used. I have no idea why gusts are reported this way. It should be understood that these measure the horizontal winds only, not the vertical winds, so a vertical windshear component cannot be measured.

Wind profilers show the winds aloft, providing details of the windspeed/direction (horizontally and vertically) and can be used to report exactly what the level and shear conditions are. How to use this information is under development.

As noted by several others, RW12L is about the least likely to encounter a wake. The conditions were right for a dry microburst.

In regards to structures, the low level ground turbulence is usually so scrambled, that structures contribute little, terrain has far more influence.

Last edited by underfire; 30th Aug 2016 at 21:49.
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Old 30th Aug 2016, 21:58
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Dubai Airport integrated weather forecasting/reporting system:

http://radiometrics.com/data/uploads/2012/11/Dubai_AWDSS.pdf

Technical Spec for Viasala Automated Weather Sensor (AWS):

http://www.vaisala.com/en/products/windsensors/Pages/WM30.aspx

Wind should be +/- 3 deg?.. However, this is rounded to nearest 10 deg for METAR purposes and possibly for tower/approach reports to pilots.. The height of the A380 capable hangars is at least 25m..more like 30m.. Distance from runway is approx 420m..

What was the wind speed and direction (vector) at the top of those hangars, moments prior to the aircraft crossing the threshold, initiating the flare, initiating the go-around, settling on to the Runway?.. Was the wind measured at 10m, different at various positions along Runway 12L?.. The geometry of the airport suggests to me that if the wind had ANY easterly component, Runway 12L is more likely to experience mechanical turbulence associated with the maintenance infrastructure?.. The question is, how much Turbuelence/Windshear based on the direction and wind speed (momentary gust wind speed/total wind at 35m, NOT 10m...) This possibility is in addition to; the elevated DA and the vertical windshear characteristic to the airport environment at the time..

Last edited by Datum; 31st Aug 2016 at 04:25.
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Old 30th Aug 2016, 22:07
  #1131 (permalink)  

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Anyone think a truthful and prompt report is likely from the UAE authorities?

I for one do not. Not in a month of Sundays.

This is a region where face-saving is more important than truth. So conjecture may as well continue.
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Old 30th Aug 2016, 22:13
  #1132 (permalink)  
 
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OMDB 030900Z 11021KT 3000 BLDU NSC 49/07 Q0993 WS ALL RWY TEMPO 35015KT 1500

The wind could have been rounded from 105 deg up to 110 deg for METAR or Tower Reported Wind.. The accuracy of the wind sensor is approximately +/- 3-5 deg.. This means the wind direction could have been in the range 100-102 deg..

The total wind speed (including momentary gust) at 10m may have been closer to 25 knots +/- error.. However, at 35m, the height of the hangar roof, the wind speed is likely to have been higher than 25 knots..
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Old 30th Aug 2016, 23:09
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I seem to remember RJTT (Tokyo Haneda) 34L and mechanical turbulence from close proximity hangars, but these are much closer to the runway touchdown area than the location of the DXB hangars to 12L.
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Old 31st Aug 2016, 00:37
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Datum, the standard for aviation winds is 10m, winds are standard at this location for takeoff and braking performance. The winds are usually measured at only one location per airport. What can be worse if they are measured at multiple locations and then averaged together.

Cup anemometers only measure the horizontal component of the wind. When it is gusting, the cups tend to overspeed and keep running past the gust, hence the 10 minute average.

As you are alluding to, winds do not always blow completely horizontally, affected by structures and terrain. The Ekman spiral is typically used in aviation (procedure design) to estimate winds aloft and the direction rotation at altitude due to the influence of terrain drag and the Coriolis effect.
Wind seldom is completely horizontal, following a Kelvin Helmholtz type pattern

so it is important that the vertical wind component be measured due to uplift/downdraft components that are typical in winds.

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Old 31st Aug 2016, 00:54
  #1135 (permalink)  
 
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Originally Posted by Underfire
The winds are usually measured at only one location per airport. What can be worse if they are measured at multiple locations and then averaged together.
Even at my backwater port we get the threshold wind, on Final, from ATC. If the other winds on the airport are majorly different, ATC will tell us. I severely doubt Dubai would not have a similar system. This "averaged" wind concept is probably a furphy.
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Old 31st Aug 2016, 00:56
  #1136 (permalink)  
 
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Datum

-3/5 degrees and a few knots will make little difference. It was a 777 that was involved and not a light single.

DXB has cup anemometers and the exact location of each of them can be found in the UAE AIP if you wish to look.
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Old 31st Aug 2016, 01:44
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Landing at Philadelphia one day, the wind was given at threshold, mid-point, and far end of the runway. All were different, the far end being 180 deg. removed from the headwind at the threshold. A 727 awaiting clearance was given permission for immediate take-off, no delay. No, said the 727 pilot, I'm going to stay here and watch this 747 land. Barsteward.
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Old 31st Aug 2016, 02:57
  #1138 (permalink)  
 
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It might be that the way many major airports are measuring wind is NO LONGER GOOD ENOUGH..especially given their propensity to also develop the associated land up to the legal limits imposed by the Obstacle Limitation Surface (OLS). These limits may not be suitable when it comes to certain combination of wind speed/direction (vector) and the proposed or existing location of large (width, height and length) buildings..

I believe many major airports globally, are using far more sophisticated AWS than those which utilise cup anemometers. I think you'll find that Dubai, and many FAA Major airports use more modern measuring equipment. See the internet links in my previous posts.

10 Minute Mean Winds have VERY LIMITED application to Flying Operations.. Note, that most aircraft crosswind limits refer to total crosswind (inclusive of GUST).. Gust Wind or a 1 Minute Maximum Sustained Wind would be far more applicable..

Aviation and Non-Aviation Infrastructure can significantly impact on an airport's wind environment, particularly when structures are adjacent to operational runways.. Note that visibility is measured at three different sections of the Runway for Low Vis Operations. It may transpire that the Aviation community should be measuring wind at multiple points around an airport..including on the roof of very large hangars or terminal buildings?..

Building Induced Turbulence and Windshear becomes a more significant issue when aircraft are limited to certain Runways due to performance issues (thrust, TODR, weight, PCN to name a few)...which may not be ideal given the prevailing wind at the time, regardless of whether the wind is a Mean Wind, Gust Wind, Total Wind...and/or whether it is measured at 10m or 35m..

All I'm suggesting is that IMHO, this issue should be EXAMINED IN DETAIL by the accident investigation team..

Further, all pilots need to educate themselves about building induced turbulence/windshear and should remain vigilant as to its presence in certain adverse wind conditions..
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Old 31st Aug 2016, 03:53
  #1139 (permalink)  
 
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in regards to PHL:

Here is the map of the data sources used for the MET at PHL, of which, there is but a single MET location for wind measurement...how the estimate the winds at each end is generated, well...







EDIT:
I believe many major airports globally, are using far more sophisticated AWS than those which utilise cup anemometers. I think you'll find that Dubai, and many FAA Major airports use more modern measuring equipment. See the internet links in my previous posts.
Your link was a Vaisala WM30, a cup anemometer. I believe you will find that most still use the cup anemometer system. While the FAA wanted replacement back in 2010, I think you will find most have not.

Bloggs..I stand corrected on YMML

They have added a second anemometer north of RW9/27 How these gives one TCH info is a bit of a stretch..

MLW1 and MLW2 shown


Last edited by underfire; 31st Aug 2016 at 04:24.
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Old 31st Aug 2016, 10:31
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Is it safe to assume pros/public being prepped to accept WS as the prime reason for this operational incident? Contemplating between intense technical discussion or being brainwashed.
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