PPRuNe Forums


Questions If you are a professional pilot or your work involves professional aviation please use this forum for questions. Enthusiasts, please use the 'Spectators Balcony' forum.

Reply
 
Thread Tools Search this Thread
Old 9th Jun 2016, 21:31   #1 (permalink)
Thread Starter
 
Join Date: May 2013
Location: EUROPE
Posts: 33
Wake turbulence time

Wake turbulence separation by time on take off. When do you take time? i´ve searched almost evereywhere and I don´t find it. thanks guys
ORICHETTI is offline   Reply With Quote
Old 9th Jun 2016, 22:27   #2 (permalink)
 
Join Date: Aug 2013
Location: PA
Age: 52
Posts: 1,357
One can use distance or time based separation. Are you looking at some of the time-based scenarios, or what is the context, that would help.

underfire is offline   Reply With Quote
Old 10th Jun 2016, 05:48   #3 (permalink)
 
Join Date: Jun 2016
Location: unknown
Posts: 6
We take the time at rotation
Sino is offline   Reply With Quote
Old 10th Jun 2016, 07:17   #4 (permalink)
 
Join Date: Jun 2000
Location: last time I looked I was still here.
Posts: 3,759
The separation is required because of vortex. These are created by lift. Thus I've always started my clock when the preceding a/c rotates. I haven't read anywhere a specific 'must do' moment. This just seemed appropriate.
RAT 5 is online now   Reply With Quote
Old 10th Jun 2016, 09:53   #5 (permalink)


Probationary PPRuNer
 
Join Date: Apr 2010
Location: Home soon
Posts: 0
If you are a M following another M…when the aircraft gets airborne(i.e. starts to make wake) then you count time (1 min- your time to get airborne..40-50)…about 10secs.
So aircraft get airborne,10 secs time check then off you go…by the time you get airborne,the leading aircraft will be 3NM in front of you.
de facto is offline   Reply With Quote
Old 10th Jun 2016, 10:57   #6 (permalink)
Thread Starter
 
Join Date: May 2013
Location: EUROPE
Posts: 33
I´ve always taken time at liftoff of the traffic, but somebody "corrected me" and i was searching for the exact moment wrotten on an official document. nothing on 8168 or on 4444 as far as i saw
ORICHETTI is offline   Reply With Quote
Old 10th Jun 2016, 11:22   #7 (permalink)


Probationary PPRuNer
 
Join Date: Apr 2010
Location: Home soon
Posts: 0
i will find the docs and give you the reference,,give me 2 days…not at home now.
de facto is offline   Reply With Quote
Old 10th Jun 2016, 13:35   #8 (permalink)
 
Join Date: Feb 2006
Location: Rapunzel's tower
Posts: 329
UK MATS Part 1

"Wake turbulence separation minima on departure shall be applied by measuring airborne times between successive aircraft. Take-off clearance may be issued with an allowance for the anticipated take-off run on the runway; however, the airborne time interval shall reflect a difference of at least the required time separation."
good egg is offline   Reply With Quote
Old 10th Jun 2016, 15:31   #9 (permalink)
 
Join Date: Jun 2000
Location: last time I looked I was still here.
Posts: 3,759
UK MATS Part 1
That's an interesting one. It would suggest ATC is responsible for separation on takeoff. Years ago I was at LGW, holding. An M was given "cleared for takeoff" behind an H. The captain of M spouted up that "You should know I need 2 mins!" Humph. ATC replied, "I only cleared you for takeoff, I didn't order you to takeoff. Take your time."
So which is it? I'd always assumed it was the pilots' responsibility on takeoff and ATC on arrival.
RAT 5 is online now   Reply With Quote
Old 10th Jun 2016, 20:04   #10 (permalink)

Only half a speed-brake
 
Join Date: Apr 2003
Location: Not home
Age: 39
Posts: 1,713
I time the preceding's positive start of rolling. Probably not scientifically exact, but good enough for me in practical terms, to reach its wake in later than two minutes. Most likely my liftoff point comes earlier as well.

The ATC has been always helpful as far as I can remember. Either delaying the take off clearance or amending it with an advisory. I suppose individual ATC's procedures may differ.

"Caution wake turbulence, behind departing XY triple-seven, cleared for take-off Rnn".
FlightDetent is offline   Reply With Quote
Old 11th Jun 2016, 06:41   #11 (permalink)
 
Join Date: Feb 2006
Location: Rapunzel's tower
Posts: 329
Quote:
Originally Posted by RAT 5 View Post
UK MATS Part 1
That's an interesting one. It would suggest ATC is responsible for separation on takeoff. Years ago I was at LGW, holding. An M was given "cleared for takeoff" behind an H. The captain of M spouted up that "You should know I need 2 mins!" Humph. ATC replied, "I only cleared you for takeoff, I didn't order you to takeoff. Take your time."
So which is it? I'd always assumed it was the pilots' responsibility on takeoff and ATC on arrival.
UK MATS Part 1
"Note: ATC shall apply the minima as prescribed above, irrespective of any pilot request for reduced wake turbulence separation. ATC does not have the discretion to reduce wake turbulence separation minima."

Unless the rules have changed since your quoted incident I'd suggest the ATCO was at fault.
good egg is offline   Reply With Quote
Old 15th Jun 2016, 08:39   #12 (permalink)
Thread Starter
 
Join Date: May 2013
Location: EUROPE
Posts: 33
so answe will be "liftoff" then? thanks!
ORICHETTI is offline   Reply With Quote
Old 15th Jun 2016, 21:31   #13 (permalink)

 
Join Date: Dec 1999
Location: LHR/EGLL
Age: 38
Posts: 4,166
RAT5,

Or perhaps the lead a/c was a 757, which if followed by any other M in the UK does not require wake turbulence separation. We used to come across that at LHR quite a bit when BA, BMI and Aer Lingus 320/737s would go wheels up behind a 757, but those same types from countries which applied the ICAO '757 is a H if followed by a M on departure' separations used to ask us for/tell us they needed 2 mins.

As has been said, UK applies rotation to rotation, and ATC cannot reduce the minima, even if the pilot wants to do so.
Gonzo is offline   Reply With Quote
Old 15th Jun 2016, 22:35   #14 (permalink)
 
Join Date: Feb 2009
Location: Seattle
Posts: 165
Doesn't brake release time separation do the trick?

As SLF it has always seemed to me that similar sized aircraft are allowing almost exactly 2 minutes between departure brake releases. Doesn't that simplify things? For some departures the visibility will be such that one cannot see the airplane ahead in the takeoff sequence at the time that it rotates. Time is time is time and takeoff speeds will be similar for similar sized planes. Allowing 2 minutes between brake releases translates very closely to the same amount of time separation between rotations and even more closely to that amount of time separation when initially airborne. Am I missing something here?
FCeng84 is offline   Reply With Quote
Old 15th Jun 2016, 23:37   #15 (permalink)
 
Join Date: Aug 2013
Location: PA
Age: 52
Posts: 1,357
Many airports use a rolling departure. Depending on the ac, some of the 4 engine variant take some time to balance.
Same issue on roll time, some take a bit of time to get moving. Yes, of course, there are plenty of airports where the follower cannot see the leader rotate. Pretty sure that ATC can see the aircraft rotate, and there is the weight off wheels broadcast.

There is wake sep, and there is the min sep to consider.
underfire is offline   Reply With Quote
Old 16th Jun 2016, 06:29   #16 (permalink)
 
Join Date: Jan 2008
Location: Reading, UK
Posts: 6,906
Quote:
Originally Posted by FCeng84 View Post
As SLF it has always seemed to me that similar sized aircraft are allowing almost exactly 2 minutes between departure brake releases. Doesn't that simplify things? For some departures the visibility will be such that one cannot see the airplane ahead in the takeoff sequence at the time that it rotates. Time is time is time and takeoff speeds will be similar for similar sized planes. Allowing 2 minutes between brake releases translates very closely to the same amount of time separation between rotations and even more closely to that amount of time separation when initially airborne. Am I missing something here?
The assumption that two "similar sized aircraft" will accelerate at the same rate on the runway and rotate at the same point at the same elapsed time after brake release isn't necessarily a valid one.
DaveReidUK is online now   Reply With Quote
Old 16th Jun 2016, 17:11   #17 (permalink)
 
Join Date: Dec 2006
Location: Florida and wherever my laptop is
Posts: 1,006
The WTC separations are all based on worst case estimates of the stability of wake vortices remaining as hazards after aircraft takes off or lands.

This is a good ad-hoc system but it can be extremely wasteful of resource if there is a crosswind that is effectively clearing the wake vortices in a few seconds yet the next aircraft sits for minutes because on a calm day the vortices may last longer.
Similarly, if there are parallel runways the vortices from one runway may interfere with aircraft on the parallel. Insisting on delays for aircraft using the same runway in that case will miss the hazard to aircraft operating on the parallel. Lots of research work has been carried out assessing these issues.

The potential cost to an airport in terms of reduced runway acceptance rates is huge. There are several l@ser based systems on the market that allow the vortices to be tracked and assessed so that only real hazards cause delays. Possibly the most advanced is WindTracer WindTracer® for Airports · Lockheed Martin which also assists the forecasters with mesoscale forecasts. It is surprising that the take up of these systems is so low.

(I do not work with LM )
Ian W is offline   Reply With Quote
Old 17th Jun 2016, 01:23   #18 (permalink)
 
Join Date: Aug 2013
Location: PA
Age: 52
Posts: 1,357
It is because LIDAR system do not work very well in the field. LIDAR systems work on the light reflecting from particulates. If there are too few, or too many, it does not work. Rain, fog, snow, etc, doesnt work. Too clear like in AUS, or too much in the air like Dubai, doesnt work.

For a system to be used, it must be real time all weather, which LIDAR takes too long to take a measurement, and far to long to process. The current crosswind/headwind systems that you mention are close, but use ground winds from the AWOS at 10m. As pilots are aware, while that is good for braking, the winds are frequently different at altitude, and windshear at low levels. That is why these methodologies have not been industrialised yet.

That being said, there are systems and methodologies that do work, and several are in the planning stages. These provide the winds up to 300m and wake measurements every 5 seconds. This will enable these systems to be used for aviation.
Currently, Phase I will by using the reduced separation on DEP with winds, and time based ARR spacing with winds. Phase II will be dynamic DEP separation using winds and wake turbulence.
An added benefit to the systems, is identifying exactly when the aircraft is right over the array (which is approx 600m from the end of the runway) thus, is t=0, visual is not required, and ATC will know exactly when the ac is over the array. If there is a splay at or near this location, ATC has the exact time when the aircraft gets to the splay point, providing another important variable to the decision making process.

Some examples:



underfire is offline   Reply With Quote
Old 17th Jun 2016, 04:16   #19 (permalink)
 
Join Date: Aug 2013
Location: PA
Age: 52
Posts: 1,357
From FAA land:

underfire is offline   Reply With Quote
Old 18th Jun 2016, 03:27   #20 (permalink)
 
Join Date: Mar 2000
Location: Australia
Posts: 735
Practical: you're waiting for the right time to start rolling, so start timing from when the preceding aircraft started rolling.
*Lancer* is offline   Reply With Quote
Reply


Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off



All times are GMT. The time now is 16:30.


© 1996-2012 The Professional Pilots Rumour Network

SEO by vBSEO 3.6.1