PPRuNe Forums - WT departure separation (crossing RWYs)

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WT departure separation (crossing RWYs)

Forgive me, but the MATS, Pt 1 has again managed to do what it does best and attempted to communicate regulations in a confusing manner.

I'm after a simple answer in terms of the number of minutes of WTS required in the UK when using cross runways.

Let's say the runways in question were 07-25 and 17-35. Aircraft A, a small departs the threshold of runway 25 and crosses the centerline of runway 35 before rotating. At what point could aircraft B, a light be launched from the threshold of 35?

Many thanks.

Wake turbulence is from when the nose wheel lifts so in this case aircraft B could be launched immediately once aircraft A has crossed rwy 35.

Thanks.

However, if the aircraft (same example) rotated before crossing the centreline, would 2, or 3 minutes WTS be used?

If it rotates before crossing I was taught use 3 minutes because it's like an intermediate point and it's better to err on the side of caution.

Extracted from MATS, Pt 1, Sec. 1, Ch. 3:

Quote:

Departures – Opposite Direction
3.54 A380. A wake turbulence separation minimum of 3 minutes shall be applied between a Light, Small or Medium (Upper and Lower) aircraft and an A380-800 aircraft when the A380-800 aircraft is making a low or missed approach and the Light, Small or Medium aircraft is:
1. utilising an opposite-direction runway for take-off; or
2. landing on the same runway in the opposite direction, or on a parallel opposite- direction runway separated by less than 760 m.
3.55 Other aircraft categories. A wake turbulence separation of 2 minutes shall be applied between a Medium (Upper and Lower), Small or Light aircraft and a Heavy aircraft, and between a Medium (Upper and Lower) or Small aircraft and a Light aircraft whenever the heavier aircraft is making a low or missed approach and the lighter aircraft is:
1. utilising an opposite-direction runway for take-off; or
2. landing on the same runway in the opposite direction; or on a parallel opposite direction runway separated by less than 760 m.
Crossing and Parallel Runways
3.56 When parallel runways separated by less than 760 m are in use, such runways are considered to be a single runway, for wake turbulence reasons, and the wake turbulence separation minima listed apply to landing and departing aircraft respectively.
3.57 The wake turbulence separation minima listed in paragraph 3.54 will apply to:
1. departures from crossing and/or diverging runways if the projected flight paths will cross; or
2. departures from parallel runways 760 m or more apart if the projected flight paths will cross.

Confusing. The paragraph about 'Crossing and Parallel Runways' makes reference to para. 3.54 - which seems totally irrelevant.

callum91: Your 3 minute separation sounds right, but I'm struggling to find where it breaks this down in the MATS.

Furthermore, I think the term 'intermediate departure' is massively miscommunicated in the MATS, Pt 1.

As I understand it, WTS for an intermediate departure means the time difference between aircraft A departing from the runway threshold and aircraft B departing from an intermediate point, somewhere further down the runway. The threshold departure is always number one.

However, the MATS goes on to say:

Quote:

Helicopters
3.62
For wake turbulence separation purposes, helicopters air taxiing across runways shall be considered to be a departure from that intermediate point of the runway.

Is this referring to the WTS required BEFORE, or AFTER the helicopter crosses? Maybe it's obvious, but I really fail to see how something so black and white as WTS cannot be communicated CLEARLY by the CAA and their publications. It really frustrates me and perhaps others...

:ugh::ugh::ugh:

Apologies for my continuing confusion, but having re-read and re-read WTS in the MATS, Pt 1, I'm seeking two answers as listed below:

Quote:

3.53 The wake turbulence separation minima in the table below shall be applied when aircraft are using:

1. the same runway; or
2. parallel runways separated by less than 760 m; or
3. crossing runways if the projected flight path of the second aircraft will cross the projected flight path of the first aircraft at the same altitude or less than 1000 ft below; or
4. parallel runways separated by 760 m or more, if the projected flight path of the second aircraft will cross the projected flight path of the first aircraft at the same altitude or less than 1000 ft below.

So it seems the magic departure WTS table applies to cross runways. What it fails to explain, however, is whether departures using cross runways are deemed intermediate departures or 'same position' departures.

So aircraft A departs the threshold of runway 25 and rotates before crossing the centreline of runway 35. Aircraft B can be launched from the threshold of runway 35 WHEN? Is it classed as an intermediate departure? If so, WHY? Where is the criteria for this laid down anywhere in the MATS?

Quote:

3.62 For wake turbulence separation purposes, helicopters air taxiing across runways shall be considered to be a departure from that intermediate point of the runway.

Secondly, as mentioned previously, does the above statement refer to WTS before or after the helicopter in question? I.e. should there be 3 minutes WTS before the helicopter is allowed to cross, or should there be 3 minutes WTS between the helicopter crossing and the departure thereafter. Or would this indeed be 2 minutes instead of 3 minutes? I think the word 'intermediate' in this statement is hugely confusing as it draws the reader to thinking 3 minutes, the WTS associated with an intermediate departure. How does a crossing helicopter in any way form an 'intermediate' departure when an aircraft thereafter departs from the runway threshold?

Apologies for the lengthy questioning and perhaps confusion, but this is frustrating me somewhat.

:confused:

Quote:

So aircraft A departs the threshold of runway 25 and rotates before crossing the centreline of runway 35. Aircraft B can be launched from the threshold of runway 35 WHEN? Is it classed as an intermediate departure? If so, WHY? Where is the criteria for this laid down anywhere in the MATS?

I would say aircraft B can be airborne 3 minutes after aircraft A. Although it doesn't make it very clear in the MATS. I would argue that it comes under aircraft departing from an intermediate point because it can't be classed as 'the same position'.

Quote:

I believe this is referring to a light helicopter that is air taxing across the runway beyond the point of rotation of a heavier aircraft meaning it will have to wait 3 minutes before doing so. You also need to consider if it was a small helicopter (e.g. S61) crossing ahead of a departing light aircraft, if the flight paths might cross then 3 minutes will be required. There is a general rule that if the projected flight paths cross at the same altitude or less than 1000ft below then WT needs to be considered.