Teaching SCA as a method
Pretty diagrams, but you're making assumptions to prove your point. In each case, your track error is the same as the correction so you end up paralleing track. In real life, you're not going to have that much error. GA aircraft are going to have a SCA of between about 45 degress at 90 knots and 30 degrees at 120 knots. You are not going to have a track error of that magnitude (I hope) so you will always be closing with track.
And don't get hung up on the maths. All you need to know is what is the SCA is for your ground speed and for how long to apply it.
It's worked for me for many years in aircraft ranging from 90 knots (Chipmunk) to 420 knots (Hawk), and it's been working well for the RAF since it was developed in WW2. I, or the RAF are not going to change the technique.
I'm bored with this. I won't look at this thread again.
And don't get hung up on the maths. All you need to know is what is the SCA is for your ground speed and for how long to apply it.
It's worked for me for many years in aircraft ranging from 90 knots (Chipmunk) to 420 knots (Hawk), and it's been working well for the RAF since it was developed in WW2. I, or the RAF are not going to change the technique.
I'm bored with this. I won't look at this thread again.
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In each case, your track error is the same as the correction so you end up paralleing track
Folowing BEagles clearly described use of SCA, one can indeed see that (using 240Kt GS) if the track error was less than 15 degrees the aircraft would move closer to the planned track but if the error was more than 15 degrees the aircraft would always continue to diverge from the planned track.
I have used errors from 7 to 120 degrees and speeds of both 90 and 240 in my various diagrams. In every case, using the order I set out gets the aircraft closer to the planned track.
Therefore, using BEagle's method, SCA is not a valid technique for regaining the planned track.
If however, the method is used correctly then it will regain track with a track error of anything from 1 to 180 degrees.
I am not asking you to change what you do. I am asking that students are given a tool that actually works and does not rely on a host of if's and but's to nearly work.
Perhaps you would like to ask someone who remembers where the RAF got it's "Standard" closing angle from and how in times past "Standard" did mean exactly that i.e. the angle did not change with GS. I actually find the original Standard Angle technique easier than this SCA that someone in the RAF copied and modified.
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groundfloor,
Double the error is a common and valid method. Beyond the half way point you can use opening and closing angles. However, this is a discussion about how SCA (which is also a valid method when properly used) is being taught to students and why I have come across many that think they are using SCA but what they are using does not work and they end up confused - (see BEagles correction drawn and explained above). Like in the diagram, the student does exactly what he instructor told them step by step but don't understand why they are further off track than when they started or why they never get back onto track even if the wind is calm.
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LOL Thats why its good to fly to a point on the horizon especially in something slow with a large drift angle - afraid the SCA has lost me in the first round - 1 in 60 works for me - old dog new tricks - will return to try understand SCA when more "alert" - seems to be groundspeed based which is cool for fast movers - well 180 +, the crawlers I flew had a rather large g/s spread over which there was little we could do ...a fully laden ALO 3 might get to 70 Kias at 3000 feet 30 deg C..
So above 20 Kts headwind it was best to stay away from roads to avoid embarressment.
So above 20 Kts headwind it was best to stay away from roads to avoid embarressment.
DFC,
I've been watching this debate with interest. There's no doubt that you are geometrically correct that modifying the SCA by the estimated track error will give a more accurate result. However, I agree with DanW that in the real world, with typical errors and distances between fixes, the "standard" standard version is absolutely fine.
What did you mean by "Perhaps you would like to ask someone who remembers where the RAF got it's "Standard" closing angle from and how in times past "Standard" did mean exactly that i.e. the angle did not change with GS."?
Geometrically, SCA=3600/GS; the concept of a standard angle that does not depend on GS is "difficult" (I'm being polite).
HFD
I've been watching this debate with interest. There's no doubt that you are geometrically correct that modifying the SCA by the estimated track error will give a more accurate result. However, I agree with DanW that in the real world, with typical errors and distances between fixes, the "standard" standard version is absolutely fine.
What did you mean by "Perhaps you would like to ask someone who remembers where the RAF got it's "Standard" closing angle from and how in times past "Standard" did mean exactly that i.e. the angle did not change with GS."?
Geometrically, SCA=3600/GS; the concept of a standard angle that does not depend on GS is "difficult" (I'm being polite).
HFD
OK, so I did look at this thread again. That's the power of PPRuNe.
I did use the 15 degree error with a 15 degree SCA, but that was just so I could plot the example on a piece of paper. I did mention that it was for illustration and that it was unlikely in real life, but anything smaller was going to be hard to draw.
The current method of teaching visual navigation was developed in WW2 when fighters were sent on low level sweeps across Europe after the battle of Briatain. The mid level techniques used prior were found to be near useless, especially when trying to make an accurate time on target. The SCA was used as a part of these techniques.
SCA is groundspeed based. At low level, you are trying to make a time on target - the parameters we were using when I was instructing was -5 +10 seconds over the target. To achieve this, you need to base your plan on a fixed GS. So in a Hawk with a plan base on 420 knots, you would need to fly an IAS of 450 in a 30 knot headwind. For this reason, the SCA doesn't change.
60knts = 60 degrees
90 knts = 45 degrees
120 knts = 30 degrees
240 knots = 15 degrees
420 knots = 8 degrees
You know your SCA before you take off, so there aren't complex calcualtions to be done in the air.
As for the LL nav technique, it's helpful to be on track, but the only time it really matters is in the last part of an attack run. For this consideration, the technique should be treate flexibly. LL nav has a large element of the TLAR technique (That Lokks About Right). For example, trying to reassess drift when your overloaded with trying to fly and look out in hills isn't easy, so "a few degrees left" based on experience will often do.
And of course, you only use the SCA method if you aren't in visual contact with something on track. Fly to a feature is the best solution every time.
The SCA got moved to the GA evironment some time ago. The club I insructed at (CFI BEagle) used it as nearly all the instructors were military QFIs (it was an RAF Flying Club). I saw some instructors make what is essentially a very simple technique very complex doing things such as calculating an SCA to with a quarter of a degree to match the GS for that leg. No one can fly that accurately - and if you do, your probably not looking out and concentrating on the task which is to get to your destiantion. You don't have to have the track between the wingtips!
I did use the 15 degree error with a 15 degree SCA, but that was just so I could plot the example on a piece of paper. I did mention that it was for illustration and that it was unlikely in real life, but anything smaller was going to be hard to draw.
The current method of teaching visual navigation was developed in WW2 when fighters were sent on low level sweeps across Europe after the battle of Briatain. The mid level techniques used prior were found to be near useless, especially when trying to make an accurate time on target. The SCA was used as a part of these techniques.
SCA is groundspeed based. At low level, you are trying to make a time on target - the parameters we were using when I was instructing was -5 +10 seconds over the target. To achieve this, you need to base your plan on a fixed GS. So in a Hawk with a plan base on 420 knots, you would need to fly an IAS of 450 in a 30 knot headwind. For this reason, the SCA doesn't change.
60knts = 60 degrees
90 knts = 45 degrees
120 knts = 30 degrees
240 knots = 15 degrees
420 knots = 8 degrees
You know your SCA before you take off, so there aren't complex calcualtions to be done in the air.
As for the LL nav technique, it's helpful to be on track, but the only time it really matters is in the last part of an attack run. For this consideration, the technique should be treate flexibly. LL nav has a large element of the TLAR technique (That Lokks About Right). For example, trying to reassess drift when your overloaded with trying to fly and look out in hills isn't easy, so "a few degrees left" based on experience will often do.
And of course, you only use the SCA method if you aren't in visual contact with something on track. Fly to a feature is the best solution every time.
The SCA got moved to the GA evironment some time ago. The club I insructed at (CFI BEagle) used it as nearly all the instructors were military QFIs (it was an RAF Flying Club). I saw some instructors make what is essentially a very simple technique very complex doing things such as calculating an SCA to with a quarter of a degree to match the GS for that leg. No one can fly that accurately - and if you do, your probably not looking out and concentrating on the task which is to get to your destiantion. You don't have to have the track between the wingtips!
Dan - SCA at 90kts is 40 deg!! (60/1.5) = 60 x 2/3 = 40.
Pretty well any system of navigation would be useless with such huge errors as a track error = SCA, as Dan has rightly pointed out.
If you find yourself 'a bit' off track and the DI isn't quite correct against the liquid compass, you don't know whether the wind or DI error caused the track error - or a bit of both. So use SCA first, then when the time is up sort out the DI error. If there is also a wind error; well, you'll just need to make a further SCA correction later - and will be on the look out for it. Blindly applying the drift angle is incorrect until you've sorted out any instrument error first after applying SCA.
SCA is a simple, easy technique which works down to about 90 kts. Even if you do use IAS for the SCA value rather than GS, it will still get you sufficiently close to your track to make a 'see it, go to it' correction.
The RAF used still-air planning for low level navigation, the wind being subject to contour effect would make much else pointless. The difference in SCA at 450 compared with 420 is less than a degree (for DFC, it's 0.5714286 deg....
), so even a 30 kt headwind isn't going to affect things much at 420KIAS. Of course in a spamcan at 90 KIAS, the difference in SCA between 90 and 60 would be 20 deg - but if you've planned accurately and flown accurately, even if you use an SCA of 40, not 60, you'll still be sufficiently close to track after making your correction.
Accurate pre-flight planning, certainly not 'MDR' pre-flight planning, together with diligent pre-HAAT and post-HAAT checks will reduce the likelihood of needing to use SCA at all.
There is no point in over-complicating a basically simple technique.....
Dan - lobster for lunch, cappuccino and chocolate sprinkles later? And regards to Mrs Dan.....
Pretty well any system of navigation would be useless with such huge errors as a track error = SCA, as Dan has rightly pointed out.
If you find yourself 'a bit' off track and the DI isn't quite correct against the liquid compass, you don't know whether the wind or DI error caused the track error - or a bit of both. So use SCA first, then when the time is up sort out the DI error. If there is also a wind error; well, you'll just need to make a further SCA correction later - and will be on the look out for it. Blindly applying the drift angle is incorrect until you've sorted out any instrument error first after applying SCA.
SCA is a simple, easy technique which works down to about 90 kts. Even if you do use IAS for the SCA value rather than GS, it will still get you sufficiently close to your track to make a 'see it, go to it' correction.
The RAF used still-air planning for low level navigation, the wind being subject to contour effect would make much else pointless. The difference in SCA at 450 compared with 420 is less than a degree (for DFC, it's 0.5714286 deg....
), so even a 30 kt headwind isn't going to affect things much at 420KIAS. Of course in a spamcan at 90 KIAS, the difference in SCA between 90 and 60 would be 20 deg - but if you've planned accurately and flown accurately, even if you use an SCA of 40, not 60, you'll still be sufficiently close to track after making your correction.Accurate pre-flight planning, certainly not 'MDR' pre-flight planning, together with diligent pre-HAAT and post-HAAT checks will reduce the likelihood of needing to use SCA at all.
There is no point in over-complicating a basically simple technique.....
Dan - lobster for lunch, cappuccino and chocolate sprinkles later? And regards to Mrs Dan.....
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Gents, I fear you may be talking yourselves into a corner. You are harping on about the advantages of SCA but are breezing over some of the problems:
It works properly with GS. Beagle, for you to just dismiss this and say IAS is good enough is simply not good enough. Take your average C152 with an optimistic IAS of 90kts. It is not unrealistic to expect 110kts GS and 70kts GS on the same navex; as you offer Beagle, what SCA is the pilot expected to use in such a scenario? If, as suggested, you use the stock 40 deg/90kt answer because that will get you 'close enough' is rather daft and not exactly delivering the 'accurate navigation' message. Other techniques such as "double the error in the direction" are actually more accurate and easier for students to understand/apply.
Maybe we should forget this fast jet nonsense and actually use techniques that are more suited to most 90kt PPL training aircraft (I had 25 deg max drift in a C152 yesterday).
It works properly with GS. Beagle, for you to just dismiss this and say IAS is good enough is simply not good enough. Take your average C152 with an optimistic IAS of 90kts. It is not unrealistic to expect 110kts GS and 70kts GS on the same navex; as you offer Beagle, what SCA is the pilot expected to use in such a scenario? If, as suggested, you use the stock 40 deg/90kt answer because that will get you 'close enough' is rather daft and not exactly delivering the 'accurate navigation' message. Other techniques such as "double the error in the direction" are actually more accurate and easier for students to understand/apply.
Maybe we should forget this fast jet nonsense and actually use techniques that are more suited to most 90kt PPL training aircraft (I had 25 deg max drift in a C152 yesterday).
Last edited by Cows getting bigger; 13th Nov 2009 at 08:18.
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HFD,
I am not modifying the SCA at all!!!
When one finds onself off the planned track there are two things that have to be done;
1. Get back on track; and
2. Fix the error so that you do not repeat the mistake.
When using SCA the order in which you do what you believe will acheive the above determines the success of the outcome.
BEagle and Dan both say - SCA first and then fix the error.
Unfortunately that can cause problems unless a series of if's and buts are in favour of the user.
I say fix the error first and then apply SCA.
As you quite correctly point out this is the only way to make the overall solution geometrically correct.
Why teach something in a way that will not work when simply by changing the order in which the unavoidable elements are completed will make it work 100% of the time?
As for the original standard angle; This was 30 degrees regardless of speed. That is why it was called standard. The reason is simple - sin 30 is 0.5. So if the correction leg is always a track that crosees the planned track at 30 degres then the leg back to track is always exactly twice as long as the distance off. Example - your planend track is 360 and you are 2nm east of track. A track of 330 for 4nm will have you back on track.
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BEagle,
Does it?
Let's try some again using your "impossible example" - 15 degree error and 4nm off track.
1 in 60 -
4nm in 15 means 16nm in 60 so error is 16 degrees. Turn towards planned track by 16 degrees. Now we are paralleling track.
How far ahead do we want to be back on track (how far along is a good feature)? - let's say 5nm
4nm in 5 means 48 in 60 so turn towards planned track again by 48(!) degrees and the aircraft will be back on track 5nm further along track.
When back on track turn opposite by this last angle and one will (should!) maintain planned track
Again it is not perfect in practice but in theory can be 100% accurate and will get the aircraft back onto or very close to the planned track.
Double the error -
Error is 15 degrees.
Turn towards planned track by 30 degrees. We will be back on in the same distance / time since we left our last checkpoint. When that time is reached turn opposite by 15 degrees and we will maintain the planned track.
The old Standard Angle -
We are 4nm off a planned track of 360. We fly a track of 330 for 8nm and we are back on track.
Seems to me that the only one that has not worked is when we exactly followed the numbered steps that you have provided.
Why is that?
I am not asking the RAF to change - as is quite correctly pointed out, at 420Kt GS the differences are vert small.
I am asking that for the students that most instructors teach (GS 30 to 300) that the teaching should be something that will always work and never end up with a student doing exactly what BEagle says to do and as per the labled drawing ending further off track than they were when they corrected.
The method used to correct must be a valid method i.e. when done step by step it must (in all cases) be capable of correcting the error.
There's no doubt that you are geometrically correct that modifying the SCA by the estimated track error will give a more accurate result.
When one finds onself off the planned track there are two things that have to be done;
1. Get back on track; and
2. Fix the error so that you do not repeat the mistake.
When using SCA the order in which you do what you believe will acheive the above determines the success of the outcome.
BEagle and Dan both say - SCA first and then fix the error.
Unfortunately that can cause problems unless a series of if's and buts are in favour of the user.
I say fix the error first and then apply SCA.
As you quite correctly point out this is the only way to make the overall solution geometrically correct.
Why teach something in a way that will not work when simply by changing the order in which the unavoidable elements are completed will make it work 100% of the time?
As for the original standard angle; This was 30 degrees regardless of speed. That is why it was called standard. The reason is simple - sin 30 is 0.5. So if the correction leg is always a track that crosees the planned track at 30 degres then the leg back to track is always exactly twice as long as the distance off. Example - your planend track is 360 and you are 2nm east of track. A track of 330 for 4nm will have you back on track.
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BEagle,
Pretty well any system of navigation would be useless with such huge errors as a track error = SCA, as Dan has rightly pointed out.
Let's try some again using your "impossible example" - 15 degree error and 4nm off track.
1 in 60 -
4nm in 15 means 16nm in 60 so error is 16 degrees. Turn towards planned track by 16 degrees. Now we are paralleling track.
How far ahead do we want to be back on track (how far along is a good feature)? - let's say 5nm
4nm in 5 means 48 in 60 so turn towards planned track again by 48(!) degrees and the aircraft will be back on track 5nm further along track.
When back on track turn opposite by this last angle and one will (should!) maintain planned track
Again it is not perfect in practice but in theory can be 100% accurate and will get the aircraft back onto or very close to the planned track.
Double the error -
Error is 15 degrees.
Turn towards planned track by 30 degrees. We will be back on in the same distance / time since we left our last checkpoint. When that time is reached turn opposite by 15 degrees and we will maintain the planned track.
The old Standard Angle -
We are 4nm off a planned track of 360. We fly a track of 330 for 8nm and we are back on track.
Seems to me that the only one that has not worked is when we exactly followed the numbered steps that you have provided.
Why is that?
I am not asking the RAF to change - as is quite correctly pointed out, at 420Kt GS the differences are vert small.
I am asking that for the students that most instructors teach (GS 30 to 300) that the teaching should be something that will always work and never end up with a student doing exactly what BEagle says to do and as per the labled drawing ending further off track than they were when they corrected.
The method used to correct must be a valid method i.e. when done step by step it must (in all cases) be capable of correcting the error.
It's simple, it works, I've been teaching it since 1989 and you'll just have to believe me that dozens of students and instructors agree.
K. I. S. S.
K. I. S. S.
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it works
In post 18, I did exactly what you said to do and ended up further off track than I was when I found the problem. Every other method would have got me back onto track. Do you not think that as a student I would be more than a bit confused ( and lost!!) after doing what you said to do?
A method that can egt the student further off track can not be valid.
Perhaps we should leave it there.
Instructors who teach SCA can decide if they are they going to teach it in a way that always gets the aircraft back onto track or (following your steps) will only do so in a limted number of cases. i.e. the other common methods will always be more reliable.
I just wonder why you prefer to limit the application of SCA which probably turns people away from a very good solution to the problem?
Finally, I hope that we can agree on one point;
SCA will move the aircraft x nm to the side of the track being flown if it is held for X minutes.
If people remember that then they can work out the rest.
Last edited by DFC; 13th Nov 2009 at 11:01.
Nope, it works using exactly the method I (and many others) were taught and have been teaching quite happily ever since.
A simple, practical way of correcting back to track to regain visual fix points.
It works. You don't need to be Euclid or Pythagoras or become involved in pointless, esoteric in flight computations, so please don't try to confuse people with pages of rather irrelevant geometry.
Having an early night after your lobster lunch, Dan......
A simple, practical way of correcting back to track to regain visual fix points.
It works. You don't need to be Euclid or Pythagoras or become involved in pointless, esoteric in flight computations, so please don't try to confuse people with pages of rather irrelevant geometry.
Having an early night after your lobster lunch, Dan......
Hi BEagle. Lobster lunch - with the company I work for? Prawn noodles actually.
Been out for dinner with some peeps you know, Tony and Lucy are in Hong Kong, and we went round Kiwi and Mary's place. They all send their regards.
And you're correct. 40 degrees for 90 knots, although when I was teaching on the Chippy, we used 20 degrees for two minutes to prevent too much change in the ETA.
SCA works well in GA aircraft. Although the GS may fluctuate, use the SCA for the planned speed and you won't be far out. Maybe a quarter of a mile at most which when looking for a turning point at 2000' is more than adequate. I spent nearly a thousand hours teaching on the Chipmunk using nothing but the SCA and it was pretty snagless.
Been out for dinner with some peeps you know, Tony and Lucy are in Hong Kong, and we went round Kiwi and Mary's place. They all send their regards.
And you're correct. 40 degrees for 90 knots, although when I was teaching on the Chippy, we used 20 degrees for two minutes to prevent too much change in the ETA.
SCA works well in GA aircraft. Although the GS may fluctuate, use the SCA for the planned speed and you won't be far out. Maybe a quarter of a mile at most which when looking for a turning point at 2000' is more than adequate. I spent nearly a thousand hours teaching on the Chipmunk using nothing but the SCA and it was pretty snagless.
Dan, we didn't use an ETA amendment on the 'dog at 120 KIAS - but I came up with the ETA correction method at 90KIAS as it was so simple.
Regards to all the peeps - it all seems so long ago now, but great days. Wish I'd put a bet on Lucy becoming the RAF's first VC10 captain - I knew she would within 15 sec of her doing her first sim trip take-off..!
Back to SCA - I also used it when in 'MAN' mode in the VC10 to regain FMS track rather than wake up the nav on those occasions when 'NAV' mode wasn't permitted. Worked just fine!
Regards to all the peeps - it all seems so long ago now, but great days. Wish I'd put a bet on Lucy becoming the RAF's first VC10 captain - I knew she would within 15 sec of her doing her first sim trip take-off..
!Back to SCA - I also used it when in 'MAN' mode in the VC10 to regain FMS track rather than wake up the nav on those occasions when 'NAV' mode wasn't permitted. Worked just fine!
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Dan,
No!!!!!. 60Kt = 90 degrees.
If you are flying at 1nm per minute and are 1nm off track, to get back onto track in 1 minute you have to fly directly towards track. Anyone who does not realise that should not be navigating solo.
Perhaps you and BEagle spent the Nav class sitting down the back chatting about lunch and friends when you should have been listening to the nav instructor.
60knts = 60 degrees
If you are flying at 1nm per minute and are 1nm off track, to get back onto track in 1 minute you have to fly directly towards track. Anyone who does not realise that should not be navigating solo.
Perhaps you and BEagle spent the Nav class sitting down the back chatting about lunch and friends when you should have been listening to the nav instructor.
Your attempts at humour are about as convincing as your obsession with unnecessary theoretical mathematics.
No-one is listening, so you'll just have to accept that those who teach SCA have done so for many years and they know it works.
Might I suggest you move on from this topic - it's getting you nowhere.
No-one is listening, so you'll just have to accept that those who teach SCA have done so for many years and they know it works.
Might I suggest you move on from this topic - it's getting you nowhere.
Last edited by BEagle; 14th Nov 2009 at 06:54.
From AP3456 Vol 7, Part 4, Sect 4, Chapter 3.
Regaining Track
14. Standard Closing Angle Technique. The standard closing angle (SCA) technique for regaining track is used when a position is fixed off track, but no feature on track is visible and no suitable funnel feature is available to assist regaining track. The SCA is based on the 1in 60 rule (see Vol 8, Pt 1, Sect 1, Chap 2) and is a closing angle determined by the speed of the aircraft. An alteration of heading equal to the SCA is made and held for a time period dependent upon the distance off track. At the end of this time period, the original heading is resumed along the required track. The SCA technique is designed to eliminate 1 nm of track error in 1 minute. Fig 6 shows an aircraft with a groundspeed of 360 kt, 1 nm to the left of track. In 1 minute the aircraft would travel 6 nm and by the 1in 60 rule:
The SCA for any groundspeeds can be found by dividing 60 by the groundspeed in nm/min. The SCA can be used to regain track by altering heading through the SCA and maintaining this heading for a number of minutes equal to the off track error in nm. In this example, being one mile off track, the aircraft turns 10º right, and after one minute will be back on track. Variations can be considered when necessary, eg by doubling the angle and halving the time or vice versa. However, using large angular corrections can lead to errors due to the breakdown of the 1 in 60 rule, to timing errors and to the fact that the changing effect of the wind on the new heading is ignored. 30º is generally considered to be the maximum heading alteration that should be employed. When it is estimated that track has been regained, alter heading to maintain the original track (allowing for any change in wind, if necessary).
Perhaps DFC, you should write to the RAF and tell them how they have been doing it all wrong for the last 65 years.
Regaining Track
14. Standard Closing Angle Technique. The standard closing angle (SCA) technique for regaining track is used when a position is fixed off track, but no feature on track is visible and no suitable funnel feature is available to assist regaining track. The SCA is based on the 1in 60 rule (see Vol 8, Pt 1, Sect 1, Chap 2) and is a closing angle determined by the speed of the aircraft. An alteration of heading equal to the SCA is made and held for a time period dependent upon the distance off track. At the end of this time period, the original heading is resumed along the required track. The SCA technique is designed to eliminate 1 nm of track error in 1 minute. Fig 6 shows an aircraft with a groundspeed of 360 kt, 1 nm to the left of track. In 1 minute the aircraft would travel 6 nm and by the 1in 60 rule:
The SCA for any groundspeeds can be found by dividing 60 by the groundspeed in nm/min. The SCA can be used to regain track by altering heading through the SCA and maintaining this heading for a number of minutes equal to the off track error in nm. In this example, being one mile off track, the aircraft turns 10º right, and after one minute will be back on track. Variations can be considered when necessary, eg by doubling the angle and halving the time or vice versa. However, using large angular corrections can lead to errors due to the breakdown of the 1 in 60 rule, to timing errors and to the fact that the changing effect of the wind on the new heading is ignored. 30º is generally considered to be the maximum heading alteration that should be employed. When it is estimated that track has been regained, alter heading to maintain the original track (allowing for any change in wind, if necessary).
Perhaps DFC, you should write to the RAF and tell them how they have been doing it all wrong for the last 65 years.
Only in the absurdly extreme case that drift hasn't been applied, the DI hasn't been synchronised correctly and the cumulative error is close to the SCA value would DFC be 'right'.
It works just fine for flights that have been correctly planned and correctly flown - yet a track error has been deduced.
Why wouldn't the heading being flown be parallel to the pre-planned heading for the leg? You work it out before flight, do your post-HAAT check and set off. Unless you've made a gross DI setting error (and didn't bother with a post-HAAT check), the track error will be due solely to the difference between actual and forecast wind velocity. Then apply SCA, when the time is up, analyse the error and apply a correction.
There is no point in trying to meddle with a simple system which has stood the test of time.
It works just fine for flights that have been correctly planned and correctly flown - yet a track error has been deduced.
Why wouldn't the heading being flown be parallel to the pre-planned heading for the leg? You work it out before flight, do your post-HAAT check and set off. Unless you've made a gross DI setting error (and didn't bother with a post-HAAT check), the track error will be due solely to the difference between actual and forecast wind velocity. Then apply SCA, when the time is up, analyse the error and apply a correction.
There is no point in trying to meddle with a simple system which has stood the test of time.
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Dan,
Thanks for that. It is a very clear description of exactly what I am trying to get across.
The diagram clearly shows that SCA is measured at the point of intersection of the planned track and the closing track. Because the dotted line in the diagram is parallel to the planned track then the angle between the dotted line (track being flown) and the closing track is also SCA.
If the dotted line was not parallel then the angles would not be the same.
Clearly as Dan shows, the RAF have got it right and those trying to copy the procedure have not followed the RAF diagram!
This is not "unnecessary theoretical mathematics" or "pointless, esoteric in flight computations". Since the exact same actions are taken following BEagles method and what I (and it seems the RAF) are describing. Therefore they are equal in terms of ease of use.
All I am trying to do is show that by a simple change in the order that the actions are done, SCA will work 100% of the time - just like the RAF diagram shows!
Is it too much to ask that students are given tools that work 100% of the time in all cases rather than only working for students that can keep their errors very small?
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The biggest argument against SCA has always been "we are not teaching fast jet flying" and "this only works for fast jets". This incorrect knock-down of a perfectly valid technique is not helped by BEagle's and other's use of SCA which only proves those that do not believe in the SCA method correct i.e. it only works for small errors (like when flying fast jets where drift is small and there is a slaved DI and often a track readout available).
Why not use SCA in a way that proves the nay sayers wrong?
Thanks for that. It is a very clear description of exactly what I am trying to get across.
The diagram clearly shows that SCA is measured at the point of intersection of the planned track and the closing track. Because the dotted line in the diagram is parallel to the planned track then the angle between the dotted line (track being flown) and the closing track is also SCA.
If the dotted line was not parallel then the angles would not be the same.
Clearly as Dan shows, the RAF have got it right and those trying to copy the procedure have not followed the RAF diagram!
This is not "unnecessary theoretical mathematics" or "pointless, esoteric in flight computations". Since the exact same actions are taken following BEagles method and what I (and it seems the RAF) are describing. Therefore they are equal in terms of ease of use.
All I am trying to do is show that by a simple change in the order that the actions are done, SCA will work 100% of the time - just like the RAF diagram shows!
Is it too much to ask that students are given tools that work 100% of the time in all cases rather than only working for students that can keep their errors very small?
---------
The biggest argument against SCA has always been "we are not teaching fast jet flying" and "this only works for fast jets". This incorrect knock-down of a perfectly valid technique is not helped by BEagle's and other's use of SCA which only proves those that do not believe in the SCA method correct i.e. it only works for small errors (like when flying fast jets where drift is small and there is a slaved DI and often a track readout available).
Why not use SCA in a way that proves the nay sayers wrong?
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BEagle,
Is that a joke?
We (I hope) teach fly a constant heading and a constant speed. Thus if everything works out i.e. calculations were correct, pilot flies exact heading and TAS, the wind is exactly as planned then the pilot will fly the planned track and there will not be any correction required.
Often however there is an error. Something is not quite as planned and the aircraft track made good (TMG) diverges at an angle from the planned track. The student discovers the error and does something to fix it. At that very moment (diverging track) they are not in the position shown in the RAF diagram.
The only case where I can imagine a student with everything happening as planned not being on the planned track i.e. TMG is paralleling planned track is when they;
A set heading from a point well to one side of the start fix; or
Mis-identify a turn point and turn early or late (what about timing!!!?)
There is a separate issue of having been on track and moving to one side to avoid something. However, in that case the pilot knows that they have moved to one side.
In all other cases, the error ocurs because there is some error and the TMG diverges from the planned track.
So why would the TMG not be parallel to planned track? - the very reason why we need to make a correction.
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Everyone reading the RAF description please note that the RAF description makes no effort to find a new heading that will kepp the aircraft on the planned track once back on track (i.e. malke sure the aircraft does not diverge again).
That is because the heading that is causing the aircraft to follow the dashed line (parallel track) will also keep the aircraft on the planned track once it gets there.
Why wouldn't the heading being flown be parallel to the pre-planned heading for the leg?
We (I hope) teach fly a constant heading and a constant speed. Thus if everything works out i.e. calculations were correct, pilot flies exact heading and TAS, the wind is exactly as planned then the pilot will fly the planned track and there will not be any correction required.
Often however there is an error. Something is not quite as planned and the aircraft track made good (TMG) diverges at an angle from the planned track. The student discovers the error and does something to fix it. At that very moment (diverging track) they are not in the position shown in the RAF diagram.
The only case where I can imagine a student with everything happening as planned not being on the planned track i.e. TMG is paralleling planned track is when they;
A set heading from a point well to one side of the start fix; or
Mis-identify a turn point and turn early or late (what about timing!!!?)
There is a separate issue of having been on track and moving to one side to avoid something. However, in that case the pilot knows that they have moved to one side.
In all other cases, the error ocurs because there is some error and the TMG diverges from the planned track.
So why would the TMG not be parallel to planned track? - the very reason why we need to make a correction.
-------
Everyone reading the RAF description please note that the RAF description makes no effort to find a new heading that will kepp the aircraft on the planned track once back on track (i.e. malke sure the aircraft does not diverge again).
That is because the heading that is causing the aircraft to follow the dashed line (parallel track) will also keep the aircraft on the planned track once it gets there.