Separation

[3rd_ear]

I thought I'd drop this in here, rather than be flayed alive by the professionals elsewhere.

This morning, I was caught in a conversation in the street with a very non-geek woman and during this, observed two aircraft on the Heathrow S-bend flying rather closely together. I think it was a BA A380 (possibly flight BA282) ahead and about three 380 lengths behind and 500 feet above, an A320 or a 737 or something. The rear aircraft was heading maybe 5 degrees to stbd of the A380, crossing its wake. I was in N5 looking east, the aircraft were maybe over Stoke Newington (N16) at that point, time about 09:50 BST.

I said "kinell, that's a bit close" and she looked up and said " they're not supposed to fly together like ducks, are they?".

At what point does this kind of adjacency qualify as a "near-miss"? Doesn't an aircraft the size of an A380 leave rather a lot of turbulence in its wake? I really didn't fancy the look of what we saw there, but I had an idea that Heathrow were trying to squish a few more in and had reduced separation or something.

Any enlightenment gratefully received.

[Gonzo]

Without knowing the situation, I'd be astounded if they weren't 1000ft apart.

Have a look at FlightRadar24.com or Heathrow's own webtrak and you can rewind to watch. While altitudes as absolute values may not be 100% accurate, the relative separation should be.

[Gonzo]

Yes, just had a look on webtrak, the BA 380 was at 5000ft, the BA 320 was at 6700ft.

[Gulf Julliet Papa]

BAW282 + BAW885 were at all times 1500ft separation, then on approach it reduces to 1000ft difference. Although 282 was for 27R and 885 for 27L. Definitely no where near a near miss

[3rd_ear]

Yes, finally worked out Webtrak - there was 1900 ft vertical between them, not an awful lot horizontal. The A380 is so big (and so A319 proportioned!), it's difficult to scale between it and other aircraft.

Still, there was lots of empty sky all around, no need to frighten the natives with antics, so I'd prefer it if they didn't get quite so close :)

[HEATHROW DIRECTOR]

Gonzo is the only contributor on here who knows what he's talking about!

[DaveReidUK]

The rear aircraft was heading maybe 5 degrees to stbd of the A380, crossing its wake. I was in N5 looking east, the aircraft were maybe over Stoke Newington (N16) at that point, time about 09:50 BST.

The tracks didn't actually cross, although from an oblique viewpoint it may have looked as if they did.

The A388 was off the Bovingdon hold, and it turned inside the A321 (off Lambourne) for 27R and 27L, respectively, as mentioned above.

At their point of closest approach (about 200m horizontally) there was around 1800' of vertical separation (give or take - WebTrak rounds heights to 100').

[kcockayne]

I thought I'd drop this in here, rather than be flayed alive by the professionals elsewhere.

This morning, I was caught in a conversation in the street with a very non-geek woman and during this, observed two aircraft on the Heathrow S-bend flying rather closely together. I think it was a BA A380 (possibly flight BA282) ahead and about three 380 lengths behind and 500 feet above, an A320 or a 737 or something. The rear aircraft was heading maybe 5 degrees to stbd of the A380, crossing its wake. I was in N5 looking east, the aircraft were maybe over Stoke Newington (N16) at that point, time about 09:50 BST.

I said "kinell, that's a bit close" and she looked up and said " they're not supposed to fly together like ducks, are they?".

At what point does this kind of adjacency qualify as a "near-miss"? Doesn't an aircraft the size of an A380 leave rather a lot of turbulence in its wake? I really didn't fancy the look of what we saw there, but I had an idea that Heathrow were trying to squish a few more in and had reduced separation or something.

Any enlightenment gratefully received.

They do not try to " squish in a few more by reducing the separation". Ever ! This type of post, although not sensationalist in its tone, perfectly illustrates the ignorance of the man on the street. I do not mean to be offensive by using that word; it's just that the poster has no understanding of what is going on but does not let that lack of knowledge deter him from making a comment.
To answer the question. Anything less than 3nm horizontally between 2 a/c at the same level, or less than 1000 ft. Vertically within 3nm of each other , during the approach phase of the flight, is classed as a lack of separation ( or Airprox); & will be subject to possible investigation. The investigation will reveal the exact degree of lack of separation & the severity of the lack of separation.

[Hotel Tango]

Still, there was lots of empty sky all around, no need to frighten the natives with antics, so I'd prefer it if they didn't get quite so close

And once given a FACTUAL answer has to resort to the above as a final say. What a load of tosh!

[3rd_ear]

There is no reason to be uncivil - or arrogant.

I think it's perfectly fair to wonder why two aircraft are vectored like that when there is evidently room not to. Is there not an issue with wingtip vortices from "heavies"? How much vertical and horizontal clearance is needed for a following aircraft to avoid these? I have heard pilots in the past on 120.4 comment on turbulence as a consequence of following a 747 down the glideslope into Heathrow, so I'd have thought an A380 would get quite a bit of elbow room on the way in.

I clearly have *some* understanding of what is going on - my "squish" comment comes from a vague memory of something changing, which was actually the 3.2 degree slope trial to do with noise rather than capacity.

[AyrTC]

If only there was an opportunity to explain separation/radar ops on some sort of t.v programme!
Rgds
AyrTC :p

[HEATHROW DIRECTOR]

3rd ear. With great respect it is abundantly clear that you have little or no understanding of how ATC works. Separation for wake turbulence is applied rigorously by ATC at all stages of flight but it can still occasionally cause problems. I worked on 120.4 for 30+ years and I can assure you that such problems are not common.

We have been assured that there was 1700ft vertical separation between the aircraft, which was more than the minimum required.

I assure you that the controllers are highly trained and they know what they are doing. It is almost impossible to estimate altitudes or ranges from other aircraft from the ground so please accept that there was no danger to anyone.

[3rd_ear]

Thanks for your input, everyone.

I've always been impressed by ATC, especially when the Heathrow "floodgates" open at 06:00 (always sounds frantically busy in a calm sort of way) and I thank you for the reassurances.

I'm not sure a telly programme would help me, not owning such a device, but a "fly on the wall" documentary about ATC would probably make rivetting viewing for those that do.

[Hotel Tango]

Pity, you just missed your chance with BBC's Skies Above Britain!

[DaveReidUK]

I've always been impressed by ATC, especially when the Heathrow "floodgates" open at 06:00 (always sounds frantically busy in a calm sort of way)

Two parallel streams of traffic coming down the ILS for both runways simultaneously is certainly an impressive sight, particularly in winter when it's dark during that hour.

I'd prefer it if they didn't get quite so closeOn reflection, probably best not to watch that either, then. :O

[Peter47]

Here is a question from a complete novice for the experts.


Is wake turbulence from an aircraft confined to its altitude or does it propagate up or down? If I am in, say, an A319 and an A380 passes 1,000 feet above or below would I suspect to encounter turbulence?

[SpringHeeledJack]

That's funny, only a few days ago I was watching an A380 coming into LHR and watched a G5 or GLEX cross over it heading into RAF Northolt and wondered to myself if there would be any wake turbulence felt by the roughly 1000ft higher biz jet ? Obviously not the same as flying/crossing directly behind the behemoth, but none the less would tree be any noticeable effects ?

[HEATHROW DIRECTOR]

There is no requirement for ATC to provide additional separation in the example you mentioned. Northolt traffic overflies Heathrow inbounds frequently with 1000 ft vertical separation. Internationally agreed separation standards are applied at all stages of flight.

[AerocatS2A]

There is no reason to be uncivil - or arrogant.

I think it's perfectly fair to wonder why two aircraft are vectored like that when there is evidently room not to. Is there not an issue with wingtip vortices from "heavies"? How much vertical and horizontal clearance is needed for a following aircraft to avoid these? I have heard pilots in the past on 120.4 comment on turbulence as a consequence of following a 747 down the glideslope into Heathrow, so I'd have thought an A380 would get quite a bit of elbow room on the way in.

The controllers job is not to spread the aircraft out evenly across the available airspace so that people on the street don't get caught out by optical illusions, rather it is to get the aircraft on the ground or off the ground in the most efficient manner possible. They have minimum separation standards and will never intentionally breach these, however if a couple of aircraft are arriving at roughly the same time then they will be sequenced close to the separation standards. The airlines and travelling public would quickly become very unhappy if aircraft were vectored around the place in order to fill the sky more fairly.

[AerocatS2A]

By the way 3rd_ear, it is statements such as bolded below that tend to cause derision from the professionals on the message board.

I think it was a BA A380 (possibly flight BA282) ahead and about three 380 lengths behind and 500 feet above, an A320 or a 737 or something.

See, you have no way of knowing what the vertical separation between the aircraft is. If you'd worded your question in a less authoritative manner then the response would be much more gentle.

[SpringHeeledJack]

Might I just interject into the thread that this sub-forum is for 'spotters' and therefore the likelihood of naive/stoopid/ridiculous questions (from the perspective of the professionals) is higher than elsewhere on pprune :-) I recall a situation over East London a few years back where a newspaper showed 2 aircraft 'almost colliding', when in fact to most on pprune it was obvious that one was going into Southend, the other holding before heading into LHR and they were more than the required 1000ft apart. As an aside I was in the jumpseat when another aircraft flew slowly past us to the side. On commenting to that it seemed closer that 1000ft, the captain informed me that the measurement was from the centre of our fuselage to theirs and with the larger aircraft with longer wingspans the distance was shorter and more impressive visually.

[HEATHROW DIRECTOR]

<<the captain informed me that the measurement was from the centre of our fuselage to theirs >>

A novel theory but no truth in it as far as ATC is concerned. Years ago some of the old radars had targets as big as half-crowns but on modern displays the target is so tiny that it would impossible to make such a measurement. Keeps the punters happy though.

[kenparry]

Is wake turbulence from an aircraft confined to its altitude or does it propagate up or down? If I am in, say, an A319 and an A380 passes 1,000 feet above or below would I suspect to encounter turbulence?

The wake always moves down. At cruise altitudes, it settles at about 800 to 1000ft below its initial altitude, so it's possible (but rare) to get some wake effect from another aircraft.