Query: Separation requirements on same SID

[Localiser Green]

Haven't been able to find anything conclusive on this, can anyone here enlighten me on the minimum separation which would apply (if any) between two aircraft departing the same runway on the same SID?

For example: Heathrow runway 27L two consecutive medium category aircraft both on a BPK7G departure.

[HEATHROW DIRECTOR]

Two minutes.

[Crazy Voyager]

Another common one in some places is 5 miles in trail

[Gonzo]

It will all depend on many factors.

Do you have surveillance or not?

Relative speeds of the pair of aircraft?

Are you really talking about separation or spacing (minimum departure interval - MDI)?

For aircraft in the same speed group, the MDI for a pair of BPKs is two minutes as HD says.

[Localiser Green]

Thanks for the responses. Yes it was departure spacing I was referring to (MDI) as opposed to 'separation'.

What about departure routings which share a common initial segment, for example BPK7G and WOBUN3G at LHR, or DVR8M / LAM4M at LGW? Would the 2 minute MDI also apply to consecutive departures in those cases (same aircraft category / relative speed assumed).

[HEATHROW DIRECTOR]

BPK and WOB would be 2 minutes. I think the second part of your Q has already been answered.

[Gonzo]

Probably more like 90 seconds for that pair at LHR, especially if the BPK is first.

[tczulu]

In my day in Terminal Control at London(not too long ago!)we would get a phone call from Heathrow Tower-"can we fire the next one off?"(with less than book separation) Mostly the answer was yes!

[HEATHROW DIRECTOR]

I've also had: "Stick with two minutes and make sure there are sixty seconds in each of them!"

Jack Frith (RIP) just used to say "Frighten me on 125.8".

[ZOOKER]

As one of my retired colleagues, (ex-EGTT, EGLL, EGKK), keeps telling me........
"It's a big sky". :ok:

[LookingForAJob]

To the OP, as you can see, there are many answers depending on one's perspective. To answer the question correctly it's important to know exactly what you are asking - and that's not intended to sound flippant. Separation is what controllers need between aircraft - in the books there are lots of different separations, and the name of the game for the controller is to have one of those separations between all of the aircraft at all times.

In a radar environment such as Heathrow, the easiest separation is 5 (or sometimes 3) between targets laterally or 1000 ft vertically. The MDI system - which takes account of the route and average speed of the class of aircraft - is designed to deliver aircraft to the radar controller, when they appear on radar, with that lateral separation minimum in place. At places without an MDI system there are other time-based separations like the two minutes that HD mentions - IIRC this would be the minimum separation for two aircraft on the same route if the first is 40kts or more faster than the second.

A tower controller also has to consider wake turbulence separation, which has become more complicated than it was when I was an operational controller - but would require two minutes for a Heavy followed by a Medium from the same point on the runway. I don't think any wake turbulence separation is required between two Mediums (but I stand to be corrected by someone who is doing it as the day job) so for the example you use it would be determined by whatever the MDI table says or when the pressure is on, whenever the receiving controller says its OK to launch the next one. I've never worked Heathrow but at my last operational unit when it was busy it was quite common for the approach controller to turn one off the SID on first contact which enabled the next to be launched maybe a minute later. If it was good wx and the tower controller could do visual separation from the VCR the second could be cleared to go when the wheels of the first left the ground if there were no other constraints.

[DaveReidUK]

I've never worked Heathrow but at my last operational unit when it was busy it was quite common for the approach controller to turn one off the SID on first contact which enabled the next to be launched maybe a minute later.

At Heathrow it's rare to see a departure turned off the SID below 4000 ft (other than CPTs on 09s) as it's then classed as "off-track" and reported as such in the stats.

[LookingForAJob]

Quite understood - my comment that I've not done LL was intended to mean that it doesn't happen there (for a number of reasons) but I could have been clearer.

[HEATHROW DIRECTOR]

Two on the same SID out of Heathrow do not require the first to be 40kts faster if they are of similar types.

This getting too complex for my old brain now! H-e-l-p Gonzo!