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Author Topic: Go arounds and aircraft spacing  (Read 9409 times)
toeknee25
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« on: March 16, 2010, 04:07:49 AM »

I run the feed here in San Antonio (KSAT) and at times I go out and plane spot for an hour or so. There are a couple times when i'm listening in and notice that as one place has just taken off, not even 1000ft in the air when another one is about 1/4 mile from landing on the same runway.

So my questions, at what point does the controller wave off the landing and ask the pilots to go around?  Do they use visual markers just by looking at the two aircraft out the tower window?

Which leads to the next question about spacing. I know larger aircraft need to have a larger gap behind them so the following aircraft isn't caught in any wake turbulence. But how does the controller (tower or approach) see this on their scopes?
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sykocus
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« Reply #1 on: March 16, 2010, 06:26:45 AM »

Not really my area of expertise, but from what I remember it depends on the category of the aircraft involved. In your case it probably involves a Category III as either the departing or arriving a/c (probably both). If that's the case then departing a/c has to be 6000' down the runway and airborne, before the arrival crosses the runway threshold. As for wake turbulence: there is no wake turbulence separation between an arrival and a departure. There is only separation between successive arrivals or successive departures. This is because there is no wake turbulence (or the FAA doesn't consider it significant) until the the departure rotates, and arrival is going to touch down way before the spot on the runway where the departure rotated so it's not going to be a factor.

I'm sure if I'm off on that someone here will correct me.

edit: fixed the horrible grammar
« Last Edit: March 16, 2010, 09:42:35 AM by sykocus » Logged

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« Reply #2 on: March 16, 2010, 09:01:55 AM »

That's pretty much it in a nutshell.  6 thousand and airborne is basic runway separation and can be used when the controller can determine the distances with visual reference points.  Or the departure can be airborne and turning to avoid any conflict; that'll work, too.  Basic radar separation is two miles between the arrival and departure IF there will be 3 miles within 2 minutes after takeoff.  If you see the departure at 1000 feet or so, he's gotta be pretty darn close to that two miles I'd guess, if not more.  Then of course there's always visual separation that can be applied as long as standard sep is ensured before and after the visual.  Like I tell anyone I train, always have something, some rule, and know what's being applied, and know where one form of sep leaves off and another picks up.  In the scenario you describe, you could very well be using different rules at different moments.
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toeknee25
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« Reply #3 on: March 16, 2010, 01:56:12 PM »

Hmm 6000 and airborne seems to be about right. The runway I noticed this from wat 3/21 which 7505 ft and of course the a/c doesn't (shouldn't) use all of it. Also the other day I noticed a SWA 737 take off then shortly have a King Air push the envelope of minimal separation. I think the 737 was turning so that answers that. They were also landing/departing a/c off from 12R which is the crossing runway so they have wanted to squeeze some more departures in... I duno. Its very interesting how they figure these things out.

I guess I didn't make myself clear on the second question. How are a/c kept apart in the air using just the scope without visual references, say in IMCs? On the scope are controllers trained on how far apart a/c really are in the air from how they appear on the scope? Do most scopes have those concentric circles that you so often see in movie depictions?

Thanks All!!   afro
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sykocus
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« Reply #4 on: March 16, 2010, 04:25:50 PM »


I guess I didn't make myself clear on the second question. How are a/c kept apart in the air using just the scope without visual references, say in IMCs? On the scope are controllers trained on how far apart a/c really are in the air from how they appear on the scope? Do most scopes have those concentric circles that you so often see in movie depictions?

Thanks All!!   afro

There are tools controllers use to judge distance. Range rings are the circles. Depending on the equipment and local SOP they may be optional, and most controllers prefer to have as little clutter as possible. You know what the distance is between certain landmarks depicted on the scope, e.g. you know how far fix ALPHA is from airport ABC. The final approach course for different approaches is usually depicted using a series of dots or dashes. The dots are usually a mile a part. If they used dashes, the dashes are usually a mile long with a mile between each one. Enroute scopes have a "J-wall". The controller can put a 5 mile circle around certain aircraft, if any other a/c are inside that circle at less then the appropriate vertical separation it's a deal. Lastly there's a function built in the every radar system I've seen where you press a key then click between two a/c on the scope and it will tell you the exact distance between them as well as the bearing from one to the other and the time between them. However those are all just tools, and after awhile you "just know" how much space is between them. You only need those tools to confirm what you know or when it's going to be close.
« Last Edit: March 16, 2010, 04:33:17 PM by sykocus » Logged

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« Reply #5 on: March 16, 2010, 04:28:22 PM »

I guess I didn't make myself clear on the second question. How are a/c kept apart in the air using just the scope without visual references, say in IMCs? On the scope are controllers trained on how far apart a/c really are in the air from how they appear on the scope? Do most scopes have those concentric circles that you so often see in movie depictions?

speaking strictly of the radar environment, you'd be back to the "2 increasing to 3" rule mentioned above (if you're still talking about an arrival and a departure.  As for eye-balling the distance on the radar display, you simply get used to it.  There are functions on the keyboard you can use that will measure the distance, but there is a school of thought on that that suggests doing that can get you in trouble because you have no out if you have less than legal, cuz now you know!  Range rings can be used, and can be centered on different points (e.g. the airport, a runway end, the radar antenna, the vor, etc) depending on what's helpful.  I use them as a guide somewhat, but keep them very faint on the display.  More helpful to me is the line drawn on the map depicting the final approach course, with dashes approximately represent a mile each.
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toeknee25
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« Reply #6 on: March 16, 2010, 07:58:29 PM »

COOL! Thanks for all the responses guys!! All my questions got answered!  grin
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« Reply #7 on: March 16, 2010, 10:15:16 PM »

Thought I'd throw my two cents in here. On most approach scopes, you can select range marks that start out from the radar center. You can select 2, 5 or 10 mile rings. On systems newer than ASR-7, you can select what we call the "J ball" which puts a 3 mile ring around a specific aircraft. The outer markers on the majority of approaches are at five miles from the airports, and on our maps, our dots on final outside of the final approach fix are spaced at two miles apart. Each of these are tools that you can use to judge the distance between two aircraft. I would have to say that, after awhile, these tools just verify what you already know, that you have the distance you need. Just by experience. Kind of like when you know to stop while parking your car without hitting the car in front of you.
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liquidoblivion
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« Reply #8 on: March 22, 2010, 01:47:40 AM »

I developed some questions about go arounds and spacing the other day while watch at CLT.  A CRJ was rotating as a 737 was flaring, it was hard to tell as the lookout is at the north end and 36C was the rwy in use, but it seemed almost that the mains of both planes were on the ground at the same time.  I wondered why the 737 didn't get the go around and how close can you get w/o having to call a go around when suddenly the 737 juiced up and took back to the sky.  Now seeing both airplanes taking to the air, one in the middle of the rwy and one at the very end so close together it seemed like to some degree it might be better as long as the departure is in rotation that you would let the arrival go ahead and land, thus keeping two aircraft from being in the air so close to each other, but I guess the idea is for the rwy to be totally free before the next guy gets a turn.  What are the specifics here??  Would anything of happened if the 737 didn't get the go around, I guess the controller would get in trouble as long as someone was paying attention.

That being said I do remember hanging out at the park just north of DCA watching arrivals on the river approach.  It was a looong time ago when I was just a kid and it was a busy evening, but man it seemed like there were a few that touched down just as one was gaining altitude and I didn't see a single go around.  Maybe they are just use to pushing the limit a little more at DCA??
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TC
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« Reply #9 on: March 22, 2010, 02:21:59 PM »

I developed some questions about go arounds and spacing the other day while watch at CLT.  A CRJ was rotating as a 737 was flaring, it was hard to tell as the lookout is at the north end and 36C was the rwy in use, but it seemed almost that the mains of both planes were on the ground at the same time. 

"almost" doesn't count.  wink  It's not a case of latitude being applied or whether or not someone's watching.  Prescribed separation must exist prior to the arrival crossing the threshold.  If I understand you correctly, the arrival went around. so that might be your answer.  maybe the rj was slow to roll, and it didn't work, so the 737 got sent around.  all other things being equal, the departure is airborne as soon as it starts to rotate.  6 thousand and airborne is likely what's applied in this scenario.  5 thousand and airborne is less, so  maybe that's why the 737 went. 
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djmodifyd
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« Reply #10 on: March 24, 2010, 08:47:29 PM »

That's pretty much it in a nutshell.  6 thousand and airborne is basic runway separation and can be used when the controller can determine the distances with visual reference points.  Or the departure can be airborne and turning to avoid any conflict; that'll work, too.  Basic radar separation is two miles between the arrival and departure IF there will be 3 miles within 2 minutes after takeoff.  If you see the departure at 1000 feet or so, he's gotta be pretty darn close to that two miles I'd guess, if not more.  Then of course there's always visual separation that can be applied as long as standard sep is ensured before and after the visual.  Like I tell anyone I train, always have something, some rule, and know what's being applied, and know where one form of sep leaves off and another picks up.  In the scenario you describe, you could very well be using different rules at different moments.

just going to chime in and say it is 2 increasing to 3 miles within ONE minute after take off...otherwise youd be correct Wink

SRS (same runway separation) depends on the type of aircraft in the situation.

there are 3 catagories, 1, 2 and 3.

when either aircraft is a CATIII (which are all jets, and some props) it is 6000 and airborne,
CATI following or preceding another CATI is 3000.
CATI following a CATII is 3000, while CATII following a CATI is 4500.

sorry if that is confusing, but that is SRS in a nutshell.

also, you can only use SRS when you can apply visual separation, if it is IFR or for some reason you cannot see both aircraft, you must use the 2 increasing to 3 rule.
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TC
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« Reply #11 on: March 25, 2010, 08:22:23 AM »

thanks!  sorry, it was a typo.
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djmodifyd
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« Reply #12 on: March 25, 2010, 01:41:20 PM »

thanks!  sorry, it was a typo.

no prob...sounds like you knew what you were talking about...just fixin the typo  afro
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MKJS Super Controller
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« Reply #13 on: April 30, 2010, 10:09:18 PM »

Greetings fellas.

I was an aerodrome/approach procedural controller at Sangster International (MKJS) for over 5 years and I now working radar approach. Let me throw something in the mix. Separation is something that for the most part tends to be at the discretion of the Authority. In other words FAA sets its rules and JCAA (Jamaica Civil Aviation Authority) sets its own. On final approach and within 10 miles of the aerodrome, aircraft must be no closer than 3 miles. Beyond that, they must be no closer than 5 miles within 60 miles of the radar head, and beyond 60 miles the separation is 10. Now if an aircraft is on a visual approach the separation is at the discretion of the following pilot. With regards to arrivals and departures, there is nothing written (such as 6,000 ft and airborne, or "2 increasing to 3") that speaks to it, except that the wheels of both aircraft should never be on the runway at the same time. Seeing that our runways in Jamaica are all under 10,000 ft, pretty much everybody is going to be airborne within 6,000 ft so that rule couldn't possibly apply apply here. Since 2003 when I first got my approach control licence, I have only ever issued a go-around instruction once. I try my best to not let it happen, with late landing clearances, S-turns, 360 turns, slow-and-dirty, you name it. For the most part, the pilots appreciate it because a missed approach procedure is the last thing anybody wants.
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