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Old 14th Sep 2010, 20:57   #1 (permalink)
 
Join Date: Apr 2010
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Visual Approach Separation in the US

It seems that at major airports in the US, traffic runs much more smoothly when the weather is nice. I think this is due to the prevalence of Visual Approaches being flown. I'm confused: since we (the airlines) are all operating under IFR, don't IFR separation standards still apply?

If a controller could explain to me why traffic moves much quicker when Visual Approaches are being conducted, as opposed to when it's low IMC, I'd be very grateful!

Much thanks,
Mike
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Old 14th Sep 2010, 21:16   #2 (permalink)
 
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Don't know what happens over there, but in the UK two aircraft (or more) conducting visual approaches can have the separation reduced if the pilots can see each other traffic. I don't suppose it happens much now, but I've seen a "sequence" of 4 aircraft all doing visual approaches. All had the runway in sight and nos 2, 3 and 4 each had the one ahead in sight. Great fun!
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Old 14th Sep 2010, 21:21   #3 (permalink)
 
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Yes, same in the US. I was aware of that, but often I'm told to maintain 5 nm spacing behind the a/c in front..so, again, how is this much different than when operating in IMC? One other possibility is tighter vectors to final? I.e., ATC can turn us in much closer...Thanks...
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Old 15th Sep 2010, 06:17   #4 (permalink)
 
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Look at your tcas and tell me there's 5 mile separation into JFK or any major American airport.
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Old 15th Sep 2010, 08:01   #5 (permalink)
 
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Quote:
I was aware of that, but often I'm told to maintain 5 nm spacing behind the a/c in front
One reason could be due to vortex wake, but then the controller should say that this is the reason. The other could be that they want to get a departure away in the gap.
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Old 16th Sep 2010, 01:25   #6 (permalink)
 
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Quote:
Look at your tcas and tell me there's 5 mile separation into JFK or any major American airport.
Depends on what the runway usage for the day is. Landing and departing the same runway is not uncommon even in the US.
If tower are departing on the same runway as arrivals...then 5nm gives them enough of a gap to get a departure away.


The visual helps traffic run smoothly when running parrallel approaches (Which alot of airports in the US do). You can have aircraft side by side on their respective ILS`s without having to worry about separation from the other aircraft...separation being the aircraft seeing the field and their parralel traffic.
In non visual conditions you cannot do this, aircraft have to be established on their respective approaches with the prescribed separation (in this case being vertical 1000ft). This will take extra vectoring to ensure aircraft intercept at the correct glideslope point that will provide separation from the parralel (aircraft at 4000ft will have to be vectored to the 5000ft intercept point to stay clear of the adjacent traffic).
It often means missing a gap on final as you can`t legally get an aircraft established without losing separation.....therefore it can`t move as quickly.

When running single runway ops ie land one depart one...I can`t see how flying a visual would speed things up that much as unless you forgo wake separation it won`t make that much difference...infact most controllers should still exercise positive control on you even on a visual especially if you are running 2.5mile spacing or something close. Nothing worse than an aircraft on the visual putting out the anchor to keep behind the one in front..and then the concertina effect starts behind. Much easier to just be packed in with efficient vectors and speed control and the controller then has an idea of who is doing what.

Next time you do a visual at a US airport check to see if they are running parralel approaches, landing and departing the same runway.
Hopefully that gives some clues as to why you are asked to do what you are.
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Old 16th Sep 2010, 07:44   #7 (permalink)
 
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With visual approaches:

Controllers can use visual separation. The controller isn't responsible for providing a given amount of separation. The only limit to how close the planes can get is the requirement that the first aircraft be off the runway when the second aircraft crosses the threshold (if not, the local controller in the tower has to send it around).

Controllers can run simultaneous visual approaches to multiple runways which would normally be prohibited due to their relative location/orientation.

Controllers don't have to worry about ensuring IFR separation for missed approaches.
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Old 17th Sep 2010, 00:02   #8 (permalink)
 
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while we're on the subject...a very basic question regarding TCAS and reduced separation.

I understand TCAS is limited to TA only when in landing config, to avoid the issue of RA against traffic they are visual with (or even on the ground).
Let's say we're flying higher up, not in landing config, say VMC climb or descent, or IFR vs VFR sort of thing, all perfectly legal and in which 2 aircraft could get very close to each other. What does the pilot do if issued an RA against traffic he's visual with?
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Old 17th Sep 2010, 06:27   #9 (permalink)
 
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You are assuming that the RA is for the traffic you see. Could it be possible that the RA is for traffic you don't see? Comply with the RA and when "clear of conflict" advise ATC of your reason to deviate.
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Old 18th Sep 2010, 04:17   #10 (permalink)


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Good question, good answers. Important thing to remember if you accept a Visual Approach Clearance from AppCon you are accepting the separation responsibility to follow the aircraft you are instructed to follow. The Controller may issue other instructions, stay 5 miles behind ( as others pointed out to make a departure slot for the Tower), issue safety advisories ie: wake turbulence, Traffic going to the parallel Rwy, speed instructions etc.
Things go faster and smoother because the situation is not as complex as when weather dictates Instrument Approaches are required.
The Herd is much easier to handle and is self separated "See Him, follow 'em, call the Twr". doing ILS's your vectored further out, more detail to speed and altitude management is required. This can be exacerbated by having to give the Twr larger departure slots as well. Instrument Approaches are simply more complicated and and require more effort on the part of ATC and Aircrew.
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