Vortex separation on departure

[Leo45]

Excuse me for this trivial question but I've increasing doubts about my answer to that one...

Let's take an exemple: when the preceding aircraft is a Heavy/ Medium and the departing aircraft ( from the same point on the runway) is a Light, a 2 min separation is required.

When dou you actually start the stopwatch: as soon as the preceding a/c rolls or lifts off the ground?

Thanks in advance.

[atcea.com]

In the U.S., the 7110.65, 3-9-6. f. states:

Separate IFR/VFR aircraft taking off behind a heavy jet/B757 departure by
2 minutes, when departing:

NOTE-
Takeoff clearance to the following aircraft should not be issued until 2 minutes after the heavy jet/B757 begins takeoff roll.
---
ATC Chat (http://atcea.com)

[10 DME ARC]

From the time the preceding a/c nose wheel lifts off the ground.
:)

[terrain safe]

from nosewheel lifting to nosewheel lifting= 2 mins

[Barnaby the Bear]

Basically as soon as the nose wheel lifts, the aircraft is producing lift and therefore those lovely vortices (is this a sucking eggs moment?)... so yep, the moment the front wheel lifts.
:8

[Spitoon]

The UK book says the spacing is the "Minimum spacing at time aircraft are airborne"

Quite straightforward rule - I guess how the controller achieves it is up to him or her.

[MrApproach]

Australia similar to UK, the leading aircraft becoming airborne is the critical point, not when it started the take off roll. Simply put, assuming a 30 sec roll, take off clearance might be given 90 secs after the lead aircraft became airborne. In fact that will give a nice buffer depending on how quick the crew are to react.

[Cuddles]

When the nosewheel lifts....

What about a big taildragger?:D

[apache43]

In Canada, we use radar separation if both depart from the same point. Light behind heavy/B757 = 6 mile.
Med behind Hvy = 5
Lgt behind Med = 4
If lighter a/c departs from intersection then we use 3 min.

[Gonzo]

apache43,

Just a quick question, you're aiming to get the appropriate number of miles separation when no.2 pops up on radar, right? To get the medium behind a heavy 5 miles gap, at which point do you clear the medium for take off?

[Barnaby the Bear]

Gonzo not quite sure what you are trying establish? Departure seperations are different from vortex. If an aircraft departs from the same point in your scenario, then 2 mins minimum. Different points 3 minutes minimum.
Once you have accounted for vortex, the departure clearence will then separate.

I.e 45 degree split after departure, the following aircraft can depart after 1 min. BUT, vortex seperation is greater, therefore that has to be taken into account.... Climb rates, IAS and routings all taken into account.

As you can see I am awful at explaining, so will never instruct.
:} plus not quite sure of your question............ Where's the pub?

[Spitoon]

It sounds like apache is using a sort of hybrid departure/vortex separation.

I would ask the question what happens if, when the second departure pops up on radar, you haven't got the rquisite space between the aircraft?

And, as I think about it some more, what assurance do you have that there is enough space between the aircraft if it takes a good few secs for the aircraft to appear on radar, say if the head is a way away?

[Ausatco]

Gonzo,

It's a matter of judgement. You clear the second for take-off when you judge that when it gets airborne the required distance will exist.

AA

[Gonzo]

Ausatco, thanks. What happens if you don't achieve the required vortex spacing (ie. a 737 pops up 4 miles behind a 747)?

Barnaby, I do realise the difference between departure route separations and vortex separations (at least I think I do! :} ). Apache43 made the point that he/she uses distance for vortex separations on departure, whereas we use time (the two or three minutes you mentioned).

[Ausatco]

Gonzo,

Firstly, just to clarify, we use both time and distance for wake turbulence separation. For example, MATS might specify 2 minutes or 5 miles. We are permitted to use whichever occurs first.

As I said for your distance question, we judge it so that when they're both airborne the distance standard is met. With a time standard, we judge it from rotate to rotate.

In Australia, wake turbulence spacing is a separation standard. If we get it wrong it's a breakdown of separation. As recovery action we have to issue traffic information and issue a "Caution, wake turbulence" to the following aircraft. The violation is an automatic report and the controller would usually be stood down.

AA

[HEATHROW DIRECTOR]

<<What happens if you don't achieve the required vortex spacing (ie. a 737 pops up 4 miles behind a 747)?>>

When I worked Heathrow Tower I used to time it from start of roll, with slight adjustment for length of roll, and only provided time separation. I thought Tower controllers were only required to provide time separation and not distance.....

[Barnaby the Bear]

An ADC only controller, you correctly state, only provides timed seperation for vortex. I also to tend judge the take off roll time to ensure maximum expedition. Usually I have to say, I am a couple of seconds over the required minima. Which as I am sure someone will point out, is better than being under. :sad:

Never did get to the pub! :{

[cossack]

you're aiming to get the appropriate number of miles separation when no.2 pops up on radar, right? To get the medium behind a heavy 5 miles gap, at which point do you clear the medium for take off?
When in your judgement you have enough space. Usually when the lead aircraft is about a mile less than the required distance away. This depends on headwind and the type of the following aircraft.
what assurance do you have that there is enough space between the aircraft if it takes a good few secs for the aircraft to appear on radar, say if the head is a way away?
The head is on the airport an coverage is excellent. With training and experience you know when to roll.
What happens if you don't achieve the required vortex spacing (ie. a 737 pops up 4 miles behind a 747)?
Doesn't happen because you wait until the spacing is 4 miles before you issue take off clearance.
I thought Tower controllers were only required to provide time separation and not distance.....
In the UK, yes, but elsewhere the rules are different. We use a Tower Radar and are trained in its use. We can provide headings to departures and missed approaches; and vector VFR aircraft in our Class C zone.

[Gonzo]

Thanks for your reply, cossack, that's more or less what I had thought.

As you say, many countries use distance instead of time to separate departures, in vortex as well as route separations. And for those saying that we don't do that in the UK, I can separate departures by five miles rather than the dictated two minutes if the departures are on converging tracks, by using my ATM.

[MrApproach]

ICAO allows controllers (Tower or other wise) to use both time or distance (measured by radar) standard for wake turbulance separation from same departure point. Time only allowed for intermediate departure. Whether your ANSP allows Towers to use radar depends on equipment and training. In UK I think you have a lot of distance to run type of Tower displays. Australia and I think US and Canada have fully functional TARs and are allowed to use them.

[apache43]

It is a matter of judgement. The separation is a minimum therefore you almost always end up with a little more because you wont roll the second aircraft until you are sure. Ocassionally, you get caught, usuallu because you have an arrival coming. You can issue a turn to the second departure immediately after takeoff to get out of the wake, but quite frankly it's already over at this point. This is a loss of separation and in our system requires reporting by the controller(s) involved. The controller(s) is removed from duty with pay and an investigation is conducted with staments and forms filled out by all. Often in this scenario, the departure controller is pulled as well becasue he/she has inherited your sep loss if you have transferred comms of both aircraft.