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Wake turbulence time standards

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Wake turbulence time standards

Old 28th May 2018, 06:53
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Wake turbulence time standards

Just curious how wake turbulence time standards are applied in the rest of the world (outside Australia)?

some background: I trained as an ATC in New Zealand and the way itís applied there is as follows (assuming a 3min standard is required) If an aircraft was to get airborne at time 00:00:13 (HH:MM:SS) the next aircraft isnít allowed to get airborne until 00:03:13.

In Australia where I now work departure time is recorded rounded to the half minute. So until recently in the example above the first aircraft gets airborne at 00:00:13 (recorded as 00:00) and the next aircraft could get airborne at 00:02:46 (recorded as 00:03) which was deemed to be three minutes between departures. A standardisation directive has recently been issued to state that this is no longer acceptable and 180seconds must apply.

I have always done it this way (180seconds) and was surprised that my colleagues have been rounding. Some of them are upset about this new directive so itís made me wonder how itís done everywhere else?
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Old 28th May 2018, 10:21
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UK.

Our manual specifices that when a separation in minutes is prescribed each full minute must be allowed to elapse, ie 1 minute=60 seconds, 2 minutes=120 seconds etc.

We time wake separation from rotation points. So if a heavy rotates at 01:01:00 a medium can rotate at the earliest 120 seconds later, ie 01:03:00.

We had a discussion recently where it seems one of our based airlines though they could not start their takeoff roll until 120 seconds had elapsed from the previous heavier aircraft rotating. This is not the case, the separation is applied between rotation as this is the point where wake is starting to be generated. This means that the clearance will be timed to anticipate the time of the takeoff roll. Therefore you will be cleared before 120 seconds has elapsed, but by the time you rotate 120 seconds will have passed since the heavier aircraft rotated.
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Old 30th May 2018, 00:14
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We time it from the start of the take off run. Gives a level of consistency. There is a timer built into the strip board; when one departure is stamped as rolling, it starts counting up to three or four minutes, depending on the WT category.

I guess it probably should be timed from the respective rotation points, but there's not that much variation in time type to type, from start of TO run to rotate...maybe a max of 30 seconds for, say, a lighty behind a heavy. (Could be more if it's something like a Cub following an IL76).
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Old 30th May 2018, 12:42
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I wasn't aware of anywhere that doesn't use the full 120sec/180sec as required. You can get away with rounding down en-route separations (sometimes) but never vortex wake when it's a life-or-death issue, let's be honest.

The difference between roll times for small to large aircraft might only be 30 sec or so, but over an hour at a high-intensity airport, that adds up to quite a lot. In the UK it's timed nosewheel rotation to nosewheel rotation, with the takeoff clearance being calculated beforehand to allow for the expected roll time, the aim obviously being to achieve as close to the 2 or 3 min without going a second under!
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Old 5th Jun 2018, 12:21
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Originally Posted by Tarq57 View Post
We time it from the start of the take off run. Gives a level of consistency. There is a timer built into the strip board; when one departure is stamped as rolling, it starts counting up to three or four minutes, depending on the WT category.

I guess it probably should be timed from the respective rotation points, but there's not that much variation in time type to type, from start of TO run to rotate...maybe a max of 30 seconds for, say, a lighty behind a heavy. (Could be more if it's something like a Cub following an IL76).
Nup. It's the time at the rotation point, as you acknowledge. Nothing to do with when your system starts timing the takeoff roll. Why would your system capture that parameter anyway? What is its purpose?
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Old 5th Jun 2018, 12:22
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Originally Posted by Crazy Voyager View Post
UK.

Our manual specifices that when a separation in minutes is prescribed each full minute must be allowed to elapse, ie 1 minute=60 seconds, 2 minutes=120 seconds etc.

We time wake separation from rotation points. So if a heavy rotates at 01:01:00 a medium can rotate at the earliest 120 seconds later, ie 01:03:00.

We had a discussion recently where it seems one of our based airlines though they could not start their takeoff roll until 120 seconds had elapsed from the previous heavier aircraft rotating. This is not the case, the separation is applied between rotation as this is the point where wake is starting to be generated. This means that the clearance will be timed to anticipate the time of the takeoff roll. Therefore you will be cleared before 120 seconds has elapsed, but by the time you rotate 120 seconds will have passed since the heavier aircraft rotated.
Spot on ...
Spot on
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Old 6th Jun 2018, 03:28
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So how do you guys estimate the time from the rotation of the heavier aircraft to the time of rotation of the lighter?
Or do you just count the full two or three (or whatever) minutes from the rotate?
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Old 6th Jun 2018, 04:39
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Originally Posted by Tarq57 View Post
So how do you guys estimate the time from the rotation of the heavier aircraft to the time of rotation of the lighter?
Or do you just count the full two or three (or whatever) minutes from the rotate?
Yes. Count from rotate time of the first, then using professional judgement, issue a takeoff clearance to the following such that its rotate time will meet the standard.
Rotate time is so close to airborne time that it can be done from logging airborne times.
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Old 6th Jun 2018, 07:01
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Originally Posted by Tarq57 View Post
So how do you guys estimate the time from the rotation of the heavier aircraft to the time of rotation of the lighter?
Or do you just count the full two or three (or whatever) minutes from the rotate?
Itís pretty straightforward once you get the hang of it, and the local conditions in terms of weather etc, to judge it to within a few seconds.

if lined up on the centreline, itís about 60s for an A380 and 747, 55 for an A330, 777, 50 for A321, maybe 45 for A320/737.....before you think about wind effects.
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Old 19th Jun 2018, 23:02
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Of course RECAT-EU departure wake turbulence separations will take a little more getting used to...only a matter of time though! (Pardon the pun!)
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