Quick separation question...

[Gin Slinger]

I've got my JAA ATPL Air Law exam tommorrow and I'd like to know if something clonking around in my head is correct...

...for two aircraft following the same localizer approach course, the minimum radar separation is 2.5nm, however for wake turbulance, 5nm must be provided.

Am I correct? I don't think I have it quite right. Can anyone give me a quick rundown on approach separation.

Cheers.

[Spitoon]

The minimum radar separation is 2.5 miles but the spacing required for wake vortex purposes depends on the WV categories (generally determined by aircraft weight) of the aircraft concerned. In some cases there is no spacing required for WV purposes.

In the UK we use a slighly different set of WV categories to those specified by ICAO but I think you'll find the ICAO ones in Doc 4444.

[HEATHROW DIRECTOR]

Minimum radar separation is usually 3nm, but under certain circumstances at certain airports 2.5nm may be used. But 2.5nm is NOT the norm. and VORTEX separation takes precedence.

The VORTEX spacing depends on the weight category of the leading a/c. Eg 737 following 747 is 5nm; 737 following 757 is 4nm; 747 following 737 could be 2.5nm as no VORTEX spacing is required.

Good luck.

[Lost_luggage34]

Heathrow Director - an uneducated question here but sometimes the Tower issues a caution warning on approach. Along the lines of ' 2.5 miles behind a 777, caution wake turbulence'.

When I have heard this, it almost sounds as if the Tower are apportioning blame to the following a/c, I know that they are not but why does that scenario occur in the first place ?

To the extreme, I once heard the Tower requesting an a/c to fly a zig-zag pattern to increase seperation on finals because of the limited distance from the preceding a/c.

Fairly familiar with the holding patterns and the flows into EGFF so not in any way a criticsm or finger pointing post - I am simply curious.

Cheers

[HEATHROW DIRECTOR]

Lost.. Sounds like one of the a/c did not fly the specified speed, as there is no way at all that anything should be 2.5miles behind a 777! If separation is eroded it can be due to many factors, eg the second a/c was slow to reduce speed.. or maybe a change in wind. There are so many factors which affect the spacing that I sometimes wonder how the hell we manage it (by "we" I mean the controllers and the crews). It's not very unusual to have a westerly wind up aloft and an easterly on the surface, or vice versa and this plays havoc! If the standard VORTEX separation is infringed crews must be warned hence the caution message.

[professor yaffle]

if a pilot is on a visual approach - the pilot is responsible for his own separation therefore the phrase " caution vortex wake recommended spacing blah blah" is used

if the aircraft is being vectored by radar then it is the controllers responsiblity to provide the vortex sep or other appropriate sep
as HD says this could be erroded for various reasons and the above phrase may be employed

HD is correct that vortex spacing takes precedence over min radar sep but bear in mind that heathrow (and another few airports as i have just found out on this thread!) use slightly different seps from the "humbler"! airfields - which have been approved

prof

[1261]

Our US friends may put me right on this but I suspect in some parts of the world the pilot is always responsible for the vortex spacing. I've certainly heard US controllers saying "cleared for the approach, caution wake turbulence - you're following a heavy triple seven".

This is obviously not the case in the UK, as HD points out. Many places in Europe expect pilots to apply departure vortex, though - Amsterdam being a good example.

[Spitoon]

So Gin, how did it go?

And did separations come up?

[Gin Slinger]

Spitoon:

The question was asked. The only sensible answer was 2.5nm, of course...20nm sounded somewhat excessive!

Raced trough a 1 hr 40 m exam in 30 minutes...luckily my groundschool's feedback was spot on this time. Just a box ticking exercise. It shouldn't be allowed! Pity Principles of Flight wasn't like it!

Thanks everybody.

[Scott Voigt]

126.1

In the US the only time that the pilot is responsible for wake turbulence in during the visual approach when on an IFR flight. We still must tell the aircraft that when he is following a HEAVY to caution the wake turbulence. Thank the lawyers for that one. Some people just don't seem to be smart enough to know that there is going to be wake behind a HEAVY.

regards

[Canoehead]

In Canada, as in the US, its the 4-5-6-4 rule for wake turbulence separation: 2 heavies=4nm, med behind heavy=5nm, light behind heavy=6nm, light behind medium=4nm. Having said that, on a visual, the pilot generally stays a tad above the glide and follow as close as he wants.

[Julioviana]

In Spain the separation for wake turbulence are the following:
heavy- heavy 4
heavy medium 5nm
heavy light 6
medium light 5
And the minimun separation on approach is 3 nm eg medium medium or light light.
When a traffic is doing a visual approach following the preceding traffic in sight, he is responsible for the separation, informing him of the type.