"rule of thumb" in procedural control
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Hi guys
It's lovely to hear the old stories about my grandpa, if you have any more please do share them and I will print them out and take them next time I visit.
Dave
It's lovely to hear the old stories about my grandpa, if you have any more please do share them and I will print them out and take them next time I visit.
Dave
Talkdown man
Malcy,
In simple terms it's __Ground speed A/c A over Ground speed A added to Ground speed A/c B. Very similar to the Critical Point formula for finding when the destination airfield is closer 'timewise' than airfield of departure etc.
In simple terms it's __Ground speed A/c A over Ground speed A added to Ground speed A/c B. Very similar to the Critical Point formula for finding when the destination airfield is closer 'timewise' than airfield of departure etc.
procedural control
I did procedural at Shanwick Oceanic whilst on my Cadet course. As far as I remember there was no complicated formula or need to take into account different speeds on reciprocal traffic.
Put simply, if one aircraft Eastbound estimated 55N 20W at 1210 & the reciprocal Westbound estimated it at 1230, then the aircraft crossed at 1220.
It doesn't matter whether the aircraft have different speeds, they are still going to cross at the same time (AFTER the Eastbound has passed the waypoint & BEFORE the Westbound has passed it). Even if one was only doing 100 kts & the other 500 kts, the crossing time would be the same.
It is immaterial that the aircraft have different speeds - that ONLY effects WHERE the aircraft cross NOT the time that they cross.
Using this, vertical separation must be established 10 minutes before (or after) this time.
Put simply, if one aircraft Eastbound estimated 55N 20W at 1210 & the reciprocal Westbound estimated it at 1230, then the aircraft crossed at 1220.
It doesn't matter whether the aircraft have different speeds, they are still going to cross at the same time (AFTER the Eastbound has passed the waypoint & BEFORE the Westbound has passed it). Even if one was only doing 100 kts & the other 500 kts, the crossing time would be the same.
It is immaterial that the aircraft have different speeds - that ONLY effects WHERE the aircraft cross NOT the time that they cross.
Using this, vertical separation must be established 10 minutes before (or after) this time.
I'm with you 2 sheds.
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Puzzled
Am I missing something here ?
If the eastbound aircraft is doing 6 miles per minute. at 1220 , it will be 60 miles east of 20W. If the westbound is doing 2 miles per minute, at 1220 it will be 20 miles east of 20W so by my reckoning they would have passed at about 1215 !
If the eastbound aircraft is doing 6 miles per minute. at 1220 , it will be 60 miles east of 20W. If the westbound is doing 2 miles per minute, at 1220 it will be 20 miles east of 20W so by my reckoning they would have passed at about 1215 !
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I am intrigued by procedural control and the CAP493 guidelines are too vague for my understanding.
When aircraft are being held in flight, the appropriate vertical separation shall be provided between holding and en-route aircraft while such en-route aircraft are within 5 minutes flying time of the holding aircraft’s flight path.
Does the above apply if you have an IFR departure and an IFR arrival (the arrival holding overhead the airfield)?
If not, what is the required separation and what does it depend on? (i.e. if the arrival is already holding when the departure takes off or what if the arrival is still on the inbound track and also does this depend on what direction they are going).
When aircraft are being held in flight, the appropriate vertical separation shall be provided between holding and en-route aircraft while such en-route aircraft are within 5 minutes flying time of the holding aircraft’s flight path.
Does the above apply if you have an IFR departure and an IFR arrival (the arrival holding overhead the airfield)?
If not, what is the required separation and what does it depend on? (i.e. if the arrival is already holding when the departure takes off or what if the arrival is still on the inbound track and also does this depend on what direction they are going).
Last edited by kpnagidi; 28th May 2013 at 20:01.
More than just an ATCO
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Not quite up to going out for moss, but remember the late Bob Cheyne plucking a strip from the display and scrutinising it very closely. "I'm looking for roots."
My old mentor at Lindholme, Les Coyle, once told me a good one.
2 aircraft northbound on Amber 1 (yes it's that old).
Aircraft A, a DC3, crosses POL 10 min ahead of Aircraft B, a DC4 = separated.
Aircraft B estimates crossing DCS 7 min ahead of Aircraft A = separated.
The 'D' man took a while to twig what happened when the DC4 asked permission to overtake the DC3 on the right!
Sorry got my VOR's mixed up; thanks Lon
2 aircraft northbound on Amber 1 (yes it's that old).
Aircraft A, a DC3, crosses POL 10 min ahead of Aircraft B, a DC4 = separated.
Aircraft B estimates crossing DCS 7 min ahead of Aircraft A = separated.
The 'D' man took a while to twig what happened when the DC4 asked permission to overtake the DC3 on the right!
Sorry got my VOR's mixed up; thanks Lon
Last edited by chevvron; 29th May 2013 at 19:59.
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Especially as POL is south of DCS 
I remember phoning Preston to complain about not getting 6-7 minute time revisions, and being told, "You're
ing lucky! We work with ing London. We don't get ing estimates!"
I remember phoning Preston to complain about not getting 6-7 minute time revisions, and being told, "You're
ing lucky! We work with ing London. We don't get ing estimates!"
Last edited by Lon More; 29th May 2013 at 07:43.
"rule of thumb in procedural control"
Off Watch,
I agree with your maths.
Perhaps my illustration was mathematically half baked & didn't serve to explain my point correctly.
What you said was basically what I was trying to get across.
It is the time that the aircraft cross when on reciprocal tracks that matters & speeds are irrelevant. ie A/C A estimates point X at 1010, A/C B estimates point X at 1020; result:- aircraft cross (on reciprocal TRs) at 1015 - when A has passed X & B is yet to get to X (the actual distances of either a/c from X being determined by their speeds)..
Speed differential simply accounts for the a/c crossing point to be further away (Or closer to) point X.
I agree with your maths.
Perhaps my illustration was mathematically half baked & didn't serve to explain my point correctly.
What you said was basically what I was trying to get across.
It is the time that the aircraft cross when on reciprocal tracks that matters & speeds are irrelevant. ie A/C A estimates point X at 1010, A/C B estimates point X at 1020; result:- aircraft cross (on reciprocal TRs) at 1015 - when A has passed X & B is yet to get to X (the actual distances of either a/c from X being determined by their speeds)..
Speed differential simply accounts for the a/c crossing point to be further away (Or closer to) point X.
kc
With respect, what you are saying could still be somewhat misleading.
But it is the speeds (groundspeeds) that determine the time - and position - at which the cross will occur or will have occurred.
But only if they happen to have the same groundspeed!
...in both time and distance. "Simply..."? - it is this calculation that requires the mathematical dexterity and understanding - and an accurate knowledge of the groundspeeds.
Regards
2 s
With respect, what you are saying could still be somewhat misleading.
It is the time that the aircraft cross when on reciprocal tracks that matters & speeds are irrelevant.
A/C A estimates point X at 1010, A/C B estimates point X at 1020; result:- aircraft cross (on reciprocal TRs) at 1015
Speed differential simply accounts for the a/c crossing point to be further away (Or closer to) point X.
Regards
2 s
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I'd offer the following, but it's been a long, long time:
In the procedural environment, one is fixated with 'fixes.' I think the argument concerning only one fix is misleading. Aircraft, in a non-radar environment, should be tracking from fix to fix. They report at one (definite), with an estimate for the next (calculated on ground speed).
For reciprocal tracks, any speed differential is irrelevant. Estimated time of passing is a calculation based on a definite report and an estimate based on the known.
Hammer me if you must, but the single fix argument clouds the issue. In procedural, 'fix to fix' is essential to safe separation - no ifs, no buts. Procedural is all about 'fixes.'
This is pretty simple:
Aircraft A reports at OBAMA at 0136 estimating DUBYA at 0215
Aircraft B reports at DUBYA at 0146 estimating OBAMA at 0219
Once again this is (essential) fix-to-fix stuff in a procedural environment.
Take the base-hour (0100) and do the following:
Aircraft A = 36+75 (the 75 is the extra 60 on the base-hour plus the 15)
Aircraft B = 46+79 (see foregoing)
Add the times up - 36+75+46+79 = 236
Divide by 4 = 59
Add to the base-hour of 0100 and ETP is 0159, then apply the 10 minutes (before/after) for level change.
In the procedural environment, one is fixated with 'fixes.' I think the argument concerning only one fix is misleading. Aircraft, in a non-radar environment, should be tracking from fix to fix. They report at one (definite), with an estimate for the next (calculated on ground speed).
For reciprocal tracks, any speed differential is irrelevant. Estimated time of passing is a calculation based on a definite report and an estimate based on the known.
Hammer me if you must, but the single fix argument clouds the issue. In procedural, 'fix to fix' is essential to safe separation - no ifs, no buts. Procedural is all about 'fixes.'
This is pretty simple:
Aircraft A reports at OBAMA at 0136 estimating DUBYA at 0215
Aircraft B reports at DUBYA at 0146 estimating OBAMA at 0219
Once again this is (essential) fix-to-fix stuff in a procedural environment.
Take the base-hour (0100) and do the following:
Aircraft A = 36+75 (the 75 is the extra 60 on the base-hour plus the 15)
Aircraft B = 46+79 (see foregoing)
Add the times up - 36+75+46+79 = 236
Divide by 4 = 59
Add to the base-hour of 0100 and ETP is 0159, then apply the 10 minutes (before/after) for level change.
Howabout
My only dispute is that it is misleading to say that "any speed differential is irrelevant". I think that would be better expressed as "any speed differential is already built in" - as you are factoring the different elapsed times over the same distance.
A single fix calculation does not cloud the argument at all - it all depends how distant or imminent (reliable) the information is. Given knowledge of the groundspeeds, you would deduce the same answer from either of your pairs of ATO/ETO.
Cheers
2 s
My only dispute is that it is misleading to say that "any speed differential is irrelevant". I think that would be better expressed as "any speed differential is already built in" - as you are factoring the different elapsed times over the same distance.
A single fix calculation does not cloud the argument at all - it all depends how distant or imminent (reliable) the information is. Given knowledge of the groundspeeds, you would deduce the same answer from either of your pairs of ATO/ETO.
Cheers
2 s
Howabout,
Your fix to fix works - it includes speed (known distance taking a certain time). Using the speeds between those fixes, using either waypoint in the calculation, also works.
Using your example:
Assume distance between fixes is 250NM – use any distance you like.
Acft A speed = 250/39*60=385KT
Acft B speed =250/33*60=455KT
Difference in time at OBAMA=43 mins
Speed slower/(speed A + speed B)* Time Differential at fix. Apply this to the time of the faster acft gives ETP. It is either added or subtracted depending on whether the waypoint you used has been passed or yet to be passed
385/(385+455)*43=19.7mins. Subtract from Bs est for OBAMA = 0159.
Using DUBYA as fix: Difference in time is 29 mins.
385/(385+455)*29=13.2mins. Add to B’s time over DUBYA=0159
Both methods give the same time.
The best thing about the grouondspeed method is that the calculation can be used between acft on tracks up to 45° apart as long as they have a common waypoint.
Your fix to fix works - it includes speed (known distance taking a certain time). Using the speeds between those fixes, using either waypoint in the calculation, also works.
Using your example:
Assume distance between fixes is 250NM – use any distance you like.
Acft A speed = 250/39*60=385KT
Acft B speed =250/33*60=455KT
Difference in time at OBAMA=43 mins
Speed slower/(speed A + speed B)* Time Differential at fix. Apply this to the time of the faster acft gives ETP. It is either added or subtracted depending on whether the waypoint you used has been passed or yet to be passed
385/(385+455)*43=19.7mins. Subtract from Bs est for OBAMA = 0159.
Using DUBYA as fix: Difference in time is 29 mins.
385/(385+455)*29=13.2mins. Add to B’s time over DUBYA=0159
Both methods give the same time.
The best thing about the grouondspeed method is that the calculation can be used between acft on tracks up to 45° apart as long as they have a common waypoint.
Last edited by topdrop; 29th May 2013 at 22:05.