Separation Tolerances
Thread Starter
Join Date: Aug 2002
Location: Aus
Posts: 2
Likes: 0
Received 0 Likes
on
0 Posts
Separation Tolerances
Everything in aviation seems to have tolerances associated with them except ATC standards. I heard that there are countries that allow a 10% tolerance on radar standards ie using 4.7Nm for a 5NM standard.
Does anyone know any examples?
Does anyone know any examples?
Join Date: Jul 2003
Location: Planet Plazbot
Posts: 1,003
Likes: 0
Received 0 Likes
on
0 Posts
As I understand the ATC standards are 1nm and 1000 feet. The tolerances are then added on depending what equipment is giving the info ie: RNAV, DME, radar, time etc. The radar 5nm is from what I remember from the tolerance of the normal ssr head at max distance (cant remember what that distance is) that being some 1.7(was a rating question i got from a certain overly officious check officer) degrees applied to both tracks which is 3.4 then rounded up to 4 then add the ATC 1nm standard and voilas 5nm. Here in AUS we have a 10 nm radar standard when the screen display is really big or the acft a long way from the head.
I
I
Guest
Posts: n/a
Radar separations were devised with the tollerance built in. I think it's usually based on a 95% probability that the aircraft will be within the planned volume of airspace. As I recall, this approach was used to develop RVSM procedures and separations. It's all based on ICAO stuff.
As toblaz says, when this probability cannot be relied upon or cannot be assured because of equipment limitations, separations are increased.
As toblaz says, when this probability cannot be relied upon or cannot be assured because of equipment limitations, separations are increased.
Mostly Harmless
Join Date: Nov 1999
Location: Oz (cold & wet bit)
Posts: 457
Likes: 0
Received 0 Likes
on
0 Posts
Or maybe even 2.7NM vice 3NM
It gets more complicated than that.
Upon verification Aircraft A tells me he is at 8,000 ft, radar says 7,800 - within tolerance. Aircraft B says 7,000, radar says 7,200 - within tolerance. The tracks cross and I have 600 ft between them on the screen, but I am using a 1,000 ft standard!
Agree with topzalp.
We also have a dumb idea here of applying a tolerance on methods used to measure the distance. If we use a Bearing Range Line measuring tool we sometime have to add a mile or two, but for comparing with the scale marker (a fictional concept denoting "eyeballing" the standard) no tolerance is required.
I once saw one approach controller stood down coz he had 5nm by eyeball (wake turb sep) and the tower had a BRL on and whined when it clicked down to 4.9. Seemed a bit silly.
It gets more complicated than that.
Upon verification Aircraft A tells me he is at 8,000 ft, radar says 7,800 - within tolerance. Aircraft B says 7,000, radar says 7,200 - within tolerance. The tracks cross and I have 600 ft between them on the screen, but I am using a 1,000 ft standard!
Agree with topzalp.
We also have a dumb idea here of applying a tolerance on methods used to measure the distance. If we use a Bearing Range Line measuring tool we sometime have to add a mile or two, but for comparing with the scale marker (a fictional concept denoting "eyeballing" the standard) no tolerance is required.
I once saw one approach controller stood down coz he had 5nm by eyeball (wake turb sep) and the tower had a BRL on and whined when it clicked down to 4.9. Seemed a bit silly.
Join Date: Jul 2001
Location: Fort Worth ARTCC ZFW
Posts: 1,155
Likes: 0
Received 0 Likes
on
0 Posts
In the US enroute facilities we have a little program called the operational error detection patch or as call it, the snitch <G>. It will tell you down the tenth of a mile if you have less than five miles required separation and then snitch on you. If you don't have another form of separation that you are using, you have bought as we call it, a deal... An investigation then follows and they determine if you indeed had less than standard separation. The approach controls do not have their own version of this, however, we can call in from the enroute facilitiy if the program goes off and we have to advise them that it did...
regards
Scott
regards
Scott
I'm Just A Lawnmower
Join Date: Aug 2002
Location: Over the hills and faraway
Age: 62
Posts: 346
Likes: 0
Received 0 Likes
on
0 Posts
HeyScott, we've got a snitch over here as well called the Separation Monitoring Function. The thing is, no one seems to agree as to what the tolerance is - some people say it is 4.9 miles, others say three and a half whilst I'm sure I heard it said that you have to get aircraft within three miles of each other before it goes off. It also takes into account areas where separation is increased away from the appropriate radar heads which means no 'cheating' over areas of the North Sea.
Anyway, no matter what the distance is, the existance of SMF makes you err on the side of caution and make sure you have every inch, plus a few more for good luck, of those five (or ten where appropriate) nautical miles.
Anyway, no matter what the distance is, the existance of SMF makes you err on the side of caution and make sure you have every inch, plus a few more for good luck, of those five (or ten where appropriate) nautical miles.
Join Date: Apr 2002
Location: Just North of France
Posts: 82
Likes: 0
Received 0 Likes
on
0 Posts
The UK SMF is set at 3.5NM or less and 600ft or less. The 600ft figure is based around the possible 400ft MODE C tolerance for levels I guess.
Also, although our blips change size outside the protected range of our RADAR's, SMF does not alter it's tolerance as it is not quite that clever.
I wouldn't recommend testing it out though, just refer to the owners manual if you are not too sure.
Also, although our blips change size outside the protected range of our RADAR's, SMF does not alter it's tolerance as it is not quite that clever.
I wouldn't recommend testing it out though, just refer to the owners manual if you are not too sure.
I'm Just A Lawnmower
Join Date: Aug 2002
Location: Over the hills and faraway
Age: 62
Posts: 346
Likes: 0
Received 0 Likes
on
0 Posts
Also, although our blips change size outside the protected range of our RADAR's, SMF does not alter it's tolerance as it is not quite that clever.
I'd agree that it is not a good idea to test it out - "the controller was testing the SMF tolerances when it went off", would not look very good on a 1261...
Moderator
Join Date: Jul 1997
Location: Europe
Posts: 3,228
Likes: 0
Received 0 Likes
on
0 Posts
As with any software, there are adaptable parameters.
Different units can set different regions to have different minimum separation standards.
Thus any 'guesses' at the actual figures may not be global ones .. or even correct for all parts of an individual units airspace.
I'd suggest we leave it at that for now.
Different units can set different regions to have different minimum separation standards.
Thus any 'guesses' at the actual figures may not be global ones .. or even correct for all parts of an individual units airspace.
I'd suggest we leave it at that for now.
Guest
Posts: n/a
If you'll allow me, a little story (belatedly) about the tolerances of SMF. (As AREA52 said, it's probably not a good idea to test it).
Shortly after the introduction of SMF in TMA (and shortly after getting my first licence, so I was easily encouraged by all my 'older and better' colleagues), I had an inbound descending to 6A, about 12nm out from final turn, with outbound from nearby airport climbing to 5A.
OK so far. Inbound screams for descent... I asked him if he was visual with the traffic (about 6 miles at this stage, 2 o'clock). Minimum looked like being about 2 miles (min in TMA 3 miles). He reported traffic in sight, and could descend with traffic in sight.
Then I had a brainwave (remembering SMF). I told him to turn off transponder 'because it sets off alarms' as I put it on the freq!
He did, descended, switched the transponder back on, and went away to approach, a happy bunny.
Five mins later the supervisor walks up...
" Who just got 1.5 miles between these two???"
Accompanied by much laughter from my dearest colleagues, I held my hand up.
Bloody thing extrapolates between last known plots, doesn't it!!!
(if any one tells you to 'switch off transponder' if they're getting tight, you now know where it comes from. B**tards never forgot it.)
Shortly after the introduction of SMF in TMA (and shortly after getting my first licence, so I was easily encouraged by all my 'older and better' colleagues), I had an inbound descending to 6A, about 12nm out from final turn, with outbound from nearby airport climbing to 5A.
OK so far. Inbound screams for descent... I asked him if he was visual with the traffic (about 6 miles at this stage, 2 o'clock). Minimum looked like being about 2 miles (min in TMA 3 miles). He reported traffic in sight, and could descend with traffic in sight.
Then I had a brainwave (remembering SMF). I told him to turn off transponder 'because it sets off alarms' as I put it on the freq!
He did, descended, switched the transponder back on, and went away to approach, a happy bunny.
Five mins later the supervisor walks up...
" Who just got 1.5 miles between these two???"
Accompanied by much laughter from my dearest colleagues, I held my hand up.
Bloody thing extrapolates between last known plots, doesn't it!!!
(if any one tells you to 'switch off transponder' if they're getting tight, you now know where it comes from. B**tards never forgot it.)
Join Date: Jun 2001
Location: southampton,hampshire,england
Posts: 869
Likes: 0
Received 0 Likes
on
0 Posts
Visual?
Did you tell the"traffic" that separation was being eroded? Did you tell "traffic" that TCAS would no longer be functional against non-transponder? In the UK we are prohibited from using visual separations of the type you suggest if Radar is available....and even with a visual confirmation of an opposite direction pass by both pilots we still have to wait for 5 miles at London ACC/Swanwick.....it helps with wake vortex spacing, but more by default than design. Don't know if your kit is similar but if I am running two on parallel headings I may put on a Range and Bearing hooked on to the pair to monitor the distance......it only reads in whole miles.....whereas the snitch on the supervisor's desk reads to a tenth.....wrong priority springs to mind!!!!!!
Join Date: Sep 1998
Location: Sydney, Australia
Posts: 513
Likes: 0
Received 0 Likes
on
0 Posts
I work C terminal airspace in Oz. If we are using ATC or pilot visual sep we are required to tell relevant IFR a/c "TCAS traffic ... (bearing, distance)... maintaining visual separation" so they know what's going on in the event of a TA.
Additionally, if the guy on visual sep will have less than standard wake turbulence separation we have to give a "Caution, wake turbulence". It seems to work a treat - everyone knows what's happening.
AA
Additionally, if the guy on visual sep will have less than standard wake turbulence separation we have to give a "Caution, wake turbulence". It seems to work a treat - everyone knows what's happening.
AA
Join Date: Jun 2001
Location: southampton,hampshire,england
Posts: 869
Likes: 0
Received 0 Likes
on
0 Posts
Radar
I'm with you on this....sometimes Radar is more of a hindrance than a help...and I particularly don't like the fact that the whole range of equipment designed to catch us out works perfectly whereas the conflict alert and prediction tools do not....especially on gradual closure at higher levels. At one time our worst problem was track jitter.....now there is so much "coasting" or "damping" that anything other than a significant turn will not register for several updates.....Progress?????/////Anyhow MATS 1 still begins with the mother-of-all-common-sense statements.
Guest
Posts: n/a
That is true at NERC (LATCC server). Elsewhere, there are much better trackers and filter systems.
STCA, as I remember is crap in London (unless it's significantly changed recently?). Constant false alerts. Poor track predictability (making vector leaders worse than useless).
There is a common ironic phrase we have :" STCA is not a control tool".
The truth is, we use it as such all the time. It works EXTREMELY well. And with on-screen cleared flight levels acting as STCA search filters, you can of course simply remove the CFL to "what-if" the effect of a continued climb/descent. No STCA: ok, off you go. If you do get one, it tells you the predicted distance down to .1 mile ish, and you can give an appropriate heading and continue climb/descent in one. Good bit of kit.
Another tool we use which is track-prediction dependent is VERA (Verification (of separation) And Resolution Advisory). Although not as accurate (of course.. you could be dealing with predictions at 10 min range), it still gives you a very good idea of when you need to give it a bit of radar handling, or when you can just lock a/c on current hdgs and look away.
Knowing what you're dealing with, it still amazes me that you push as much traffic as you do. But, with a little investment, I think simple tools would help you a great deal.
As you say, what does SMF do at the time? Buggar all.
Once again, wrong priorities!
STCA, as I remember is crap in London (unless it's significantly changed recently?). Constant false alerts. Poor track predictability (making vector leaders worse than useless).
There is a common ironic phrase we have :" STCA is not a control tool".
The truth is, we use it as such all the time. It works EXTREMELY well. And with on-screen cleared flight levels acting as STCA search filters, you can of course simply remove the CFL to "what-if" the effect of a continued climb/descent. No STCA: ok, off you go. If you do get one, it tells you the predicted distance down to .1 mile ish, and you can give an appropriate heading and continue climb/descent in one. Good bit of kit.
Another tool we use which is track-prediction dependent is VERA (Verification (of separation) And Resolution Advisory). Although not as accurate (of course.. you could be dealing with predictions at 10 min range), it still gives you a very good idea of when you need to give it a bit of radar handling, or when you can just lock a/c on current hdgs and look away.
Knowing what you're dealing with, it still amazes me that you push as much traffic as you do. But, with a little investment, I think simple tools would help you a great deal.
As you say, what does SMF do at the time? Buggar all.
Once again, wrong priorities!