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Wake turbulence separation

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Wake turbulence separation

Old 21st Mar 2018, 09:10
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Wake turbulence separation

Good day all,

I have a doubt. There are basically two procedures
- RADAR separation
- TIME based separation

Let's assume we're departing from an airport where separation is based on radar.
Are we supposed to respect the time constraint as well??

Ex: cleared for T/O by Tower (I can see on the ND that the preceding ac is at least 5Nm ahead). However, the time constraint (2 or 3min) is not elapsed yet.

Can we take off??

(I presume that's a NO, but I can't find any explicit document)

Last edited by Feather44; 25th Mar 2018 at 05:11.
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Old 21st Mar 2018, 12:42
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Australian AIP has the following:
Where the required separation can be determined by distance using an aircraft report or ATS Surveillance System, ATC need not apply the time standard to an affected:
a. arriving aircraft
b. departing aircraft, unless it is departing from an intermediate point as described in para 9.2.2
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Old 21st Mar 2018, 13:01
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UK case, ATC shall apply the time seaparation for VORTEX WAKE, but can use a little bit of anticipation too, below from MATS 1

9F. Departures
9F.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.

Therefore, even in Dubai, I hope you will not get a clearance that means less than the required minimum time between departures.
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Old 21st Mar 2018, 13:40
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Muddied by the fact that certain areas of the UK CAA misinterpreted ICAO Doc4444 a few years ago and mandated that as well as applying time-based wake turbulence departure separations (which states there is no departure wake separation required between two Heavies), airports should also apply a 4nm distance-based wake separation between Heavy aircraft.

Thankfully we've moved to RECAT EU so can forget that.

Not the CAA's finest hour.
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Old 21st Mar 2018, 17:00
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Let's assume we're departing from an airport when separation is based on radar.
Are we supposed to respect the time constraint as well??
Will the radar dissipate the wake vortex faster? The wake turbulence separations are designed to avoid aircraft upsets that may not be within the pilot's ability to handle. In my view they trump IFR separations.
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Old 21st Mar 2018, 18:05
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You would not be cleared for take-off at DXB without the appropriately timed vortex wake spacing.
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Old 22nd Mar 2018, 00:08
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The distance is fine. The time is there for when the distance cannot be determined. There are situations such as intermediate departures where time must be used.

Unless you feel that the situation is unsafe or the controller has made an error your takeoff clearance covers you.
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Old 22nd Mar 2018, 06:11
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@Pera, the timed vortex wake separation MUST be applied if required, it trumps ANY other requirement.

There is no substitution of distance based separation for DEPARTURES in the UK, or as Tower Ranger confirms, in Dubai where the OP was asking about.
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Old 22nd Mar 2018, 08:02
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Will the radar dissipate the wake vortex faster?
Nice mansplaining. No wonder you are looking for a job. You are aware there are distance wake separation standards?

What I find interesting about the Australian use of a distance standard is: How is the distance determined? I'm assuming you have the first departure identified by radar- how are you determining the distance to the second? Is there a 'deemed' separation from the runway end, or the airfield reference point? Are both aircraft identified? Or.......?
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Old 22nd Mar 2018, 16:57
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Originally Posted by The Fat Controller View Post
@Pera, the timed vortex wake separation MUST be applied if required, it trumps ANY other requirement.

There is no substitution of distance based separation for DEPARTURES in the UK, or as Tower Ranger confirms, in Dubai where the OP was asking about.
The OP is a pilot with a take off clearance, not an ATCO. Unless there was a particular reason to assume the wake risk was increased then the pilot can assume that the tower has it covered. Wheels up to wheels up!
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Old 22nd Mar 2018, 19:33
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Thanks for your inputs guys!
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Old 23rd Mar 2018, 12:46
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Originally Posted by Pera
The OP is a pilot with a take off clearance, not an ATCO. Unless there was a particular reason to assume the wake risk was increased then the pilot can assume that the tower has it covered. Wheels up to wheels up!
I'm not sure that it is valid to say that you can assume the tower has it covered in all parts of the world.

And I think you may find a few pilots who might point out that as they're responsible for the aircraft they might be inclined to double-check what ATC or anyone else does rather than assume it's OK.
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Old 23rd Mar 2018, 13:01
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Originally Posted by LookingForAJob View Post
I'm not sure that it is valid to say that you can assume the tower has it covered in all parts of the world.
Whilst this may be true, the important thing is wheels up to wheels up and NOT wheels up - wait 2 minutes - then cleared for take-off.
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Old 23rd Mar 2018, 15:35
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The OP is a pilot with a take off clearance, not an ATCO. Unless there was a particular reason to assume the wake risk was increased then the pilot can assume that the tower has it covered. Wheels up to wheels up!
Well I think this is another one of those cases where two parties both have the responsibility. A bit like being vectored when the PIC still has responsibility to maintain situational awareness. Or when VFR the right of way aircraft still has a responsibility to avoid the collision.
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Old 23rd Mar 2018, 17:23
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<<And I think you may find a few pilots who might point out that as they're responsible for the aircraft they might be inclined to double-check what ATC or anyone else does rather than assume it's OK. >>

I can recall only one instance of a pilot querying my decision - and that was on radar where he thought a strobe light was a bit close and it was over 10nm away! At busy units there wouldn't be the available R/T time for pilots to double-check instructions.
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Old 12th Apr 2018, 05:12
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Originally Posted by Feather44 View Post
Good day all,

I have a doubt. There are basically two procedures
- RADAR separation
- TIME based separation

Let's assume we're departing from an airport where separation is based on radar.
Are we supposed to respect the time constraint as well??

Ex: cleared for T/O by Tower (I can see on the ND that the preceding ac is at least 5Nm ahead). However, the time constraint (2 or 3min) is not elapsed yet.

Can we take off??

(I presume that's a NO, but I can't find any explicit document)
The answer is YES. ATC will have applied the applicable standards between you and the preceding aircraft. A pilot in command is ultimately responsible for the safety of the operation, but hesitating on the runway is not generally a good contributor to safety a a busy airport.

Wake separation between successive departures, either time or distance, is based on rotation point, not wheels up or other things as suggested. ATC will apply the most efficient standard available, cognisant of wake turbulence and physical separation minima and take into account other factors such as aircraft performance relative to the preceding aircraft and clearance (such as are they following the same SID or are the turns after airborne different). Remember that the tower controller can usually see at least the aircraft on the ground out the window and will use the situation display to confirm the position of the airborne aircraft. Timers are used where required.

As an aside, let's get away from the old fashioned concept of radar, too. Position information is frequently derived from other technologies such as MLAT and plain ADS-B as well (both of which are more accurate than radar) and data is from various sources is fused by software to display the most accurate position to the controller.
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