PDA

View Full Version : Teaching SCA as a method


DFC
6th Nov 2009, 20:44
This is not a for or against thred.

The general way that SCA is being taught is explained by BEagle in this thred;

http://www.pprune.org/flying-instructors-examiners/382335-pilot-navigation.html

I agree that SCA is a good valid method of correction when properly used

However, very few pilots seem to use SCA correctly and unfortunately I believe and having read BEagle's explanation in the above thred even more believe that the instructors who teach this technique don't apply it correctly.

Let me explain;

Here is a quote from BEagles explanation;


Using the SCA technique is very straightforward. Let us imagine that we have been accurately flying the first leg of our navigation exercise at 90 kts on a heading of 040° when we notice that we are 4 miles left of track with some 7° of drift error as deduced from our single 10° fan line. The first correction is to turn right onto a heading of 080° and then to time for 4 minutes as we head back towards track. During this 4 minutes we can first reassess that it really was a 4 mile error and then jot down on the log that our ETA at the turning point will be 4/3 of a minute later than calculated and that there’ll be a 7° drift correction to apply when we’re back on track. When our 4 minutes are up, we turn back onto our original heading plus our drift correction, i.e. on to 047° in this example and recheck that the DI is properly aligned with the magnetic compass. With any luck and assuming that the wind doesn’t change yet again, our navigation exercise should now continue pretty well on track and we should only need to note the passing of visual fix points to revise the ETA at the turning point.



The problem is that the above is an incorrect explanation of how to use SCA and following the technique above exactly will never get the aircraft back onto track.

In fact even ignoring the effect that turning more into wind will have, following the above explanation will always result in the aircraft being still off track and also further along track than expected. The magnitude of this error caused by following the above explanation is directly proportional to the initial error.

The solution;

SCA in both theory and practice assumes that at the point where the aircraft is turned by the SCA angle it is paralleling the desired track. In other words the error in the above is that the theory measures the error miles at 90 degrees to the desired track despite the fact that the aircraft is diverging from it.

The fix is very simple;

BEagle in the above example noticed that after some time there was an error of 7 degrees and the aircraft was 4nm off track.

The first action must be to parallel track i.e. in this case turn towards the required track by 7 degrees.

Now the aircraft is paralleling the desired track and you can correctly apply the SCA and ignoring the wind effect it will work.

So actions;

1. Determine tracking error and turn towards track by the error (drift line or 1 in 60 which ever you want).

2. Turn towards the desired track by the SCA and maintain this heading for a number of minutes equal to the number of miles off track.

3. Turn in the opposite direction by the SCA - you have already corrected the drift before so no need to do it again now.

So using BEagles example;

1. Turn right by 7 degrees (parallel track) Heading = 047

2. Turn right by SCA for 4 minutes Heading = 087

3 When the 4 minutes are up turn left by SCA. Heading = 047.

So please ensure that whatever method you teach for track correction that it (in theory) will have the ability to regain track.

Saves us trying to explain (to someone who uses an SCA of 30 degrees and tries BEagles exact method when the error is 30 degrees) why they will never ever regain track because they are now paralleling it!!!! :ugh:

BEagle
8th Nov 2009, 16:02
Strange, it seems to work perfectly well in practice.....:hmm:

DFC
8th Nov 2009, 17:34
Strange, it seems to work perfectly well in practice


Something must be wrong then because if you sit down and draw it on paper, unless the process you describe is commenced from a position where the TMG is paralleling the desired track then simple trig shows that it can't work.

For the method to be valid it must at least in theory get the aircraft back onto track. If it can't do it in theory then the method is not valid because it fails to do what it is designed to do.

For the method to work in both theory and practice, the first step must be to parallel the desired track.

The method is sound. Just the application (as per your exact description) seems to have a minor flaw.

The steps are simple;

1. Deduce track error. and turn by this error towards the desired track.

2. Measure distance off track (this will no longer be an increasing figure).

3. Turn by SCA towards track and hold for time in minutes = distance off

4. When time up, Turn by SCA in the opposite direction to maintain desired track.


Unfortunately, your explanation and the method many are using is to do the following;

Bloggs is 3nm right of track with a 10 degree error.

Bloggs turns left by SCA and hold this for 3 minutes.

Bloggs think that they are back on track but they are not. They are 3nm to the left of the track they they had been flying.

Let's use a method that really does have the potential to get the flight back on track.

As I said, draw it on paper and see that the TMG must parallel desired track for it to work. It is not a big problem and means that when correctly applied once back on track the pilot does not have to remember what the error was all they have to do is turn by the SCA again but in the opposite direction.

DFC
11th Nov 2009, 12:39
I gather from the lack of a response that you may be confused BEagle so I have managed to draw a diagram which should make it easier to understand;

http://i889.photobucket.com/albums/ac100/pprunedfc/SCA.jpg

In both cases the pilot departed A for Z and after some time found themselves about 3nm off track.

In the first case, the pilot turns through the SCA for 90Kt and flies that for 3 minutes (4.5nm). During this time they deduce the error and when they think they are back on track they correctly fly the correct heading.

In the second case the pilot first corrects the error and then applies the SCA.

What is common to both examples is that

a) the pilot is 3nm right of the desired track when the SCA is used; and

b) By applying the SCA the pilot moves the aircraft 3nm left of the track being followed when the turn was made

However, because in the first case the track being followed is diverging from the desired track there is an error induced and simple trig shows that SCA can never get the aircraft back onto the desired track.

Therefore to correctly apply SCA, the first action must be to get rid of the error (parallel desired track)

Hope that makes my point clearer?

Dan Winterland
11th Nov 2009, 13:49
DFC, I'm not sure you understand what BEagle is saying. He wrote "Let us imagine that we have been accurately flying the first leg of our navigation exercise at 90 kts on a heading of 040° when we notice that we are 4 miles left of track". You wrote "In the second case the pilot first corrects the error and then applies the SCA".

BEagle has told us that we have been flying accurately, therfore the error is not through flying an incorrect heading - it's down to applying the wrong drift correction, probably due to an inaccurate forecast. If this is the case, the correction needs to be applied when back on track. If the error is because we realise we have been flying the wrong heading for whatever reason, then it's quite obvious that we will have to make some sort of heading correction before applying the SCA.

You actually demonstrate this in your second diagram where you show a heading adjustment, whereas your first diagram is incorrect in that if you continued on your original heading, you will in fact still diverge from track. You do however, correctly state that the heading error itself will lead to a slight displacement. However, this will be small and in the overall scheme of things, accurate enough to get you within visual range of your next turning point.


SCA does work very well in practice. The technique was designed for military pilots operating in the low level environment where navigation is made far more difficult because you can't see your turning or check points until you are close to them and also because the workload is high. When you determine you have a track displacement error, you have to decide what caused it. Was it a cumulative error down to innacurate drift calculation, or was it a once only error due to having to avoid weather/a SAM site or as a result of evading an enemy fighter? In the former, a correction has to be made before applying the SCA , in the latter - the original heading was probably good and no correction is neccessary.

I learnt it when I trained in the RAF and then later taught it as an RAF QFI for 6 years. With lots of experience of the SCA, I would say it's a very good technique. Although it's probably of more relevance in a Tucano flying at 250' at 240knts, it is still very valid at lower speeds. Thats why I later taught it in the flying club environment. I found it superior and easier for a student to apply than other techniques such as the new track reference.

Cows getting bigger
11th Nov 2009, 16:53
.... and you guys wonder why some of us avoid SCA? :)

DFC
11th Nov 2009, 16:59
Dan,

I think that you have missed the whole point.

SCA is based on tracks and right angle triangles formed by tracks.

It makes little difference why the track made good (TMG) is not equal to the planned track. The important thing is that they are not the same some something has to be done.

To describe it 100% correctly, in zero wind, SCA will move the aircraft Xnm to the side of the track currently being flown if the SCA track is held for X minutes.

In the first diagram and the second diagram, the SCA moves the aircraft 3nm to the left of the track being flown at the time when it is started. However, as can been clearly seen from the first diagram, moving the aircraft 3nm to the left of a diverging TMG will never put it back on the planned track. - That is simply impossible because due to the divergence, the distance between the TMG and the planned track is increasing all the time.

Correcting the error first causes the TMG to parallel the planned track. Therefore, if the distance between the two parallel tracks is converted into time for the SCA, the SCA will get the aircraft back onto the planned track.

Again I say that this has nothing to do with headings. It is a track issue. The 18 degree track error in the above could be caused by;

Incorrectly set DI,

Correctly set DI but wrong heading flown

Wind stronger than planned

Wind not as strong as planned

Compass telling lies!!!

It makes little difference to the theory because the whole theory is based on tracks.

The procedure will not be 100% accurate with winds unless one adjusts the headings and timings for wind efffects - again I say that it is a track procedure. However, over short times in relatively light winds, it will not be that far out - provided that the procedure is correctly used.

Finally, Replace the above track error with 40 degrees!!

In example 1, the SCA track would initially parallel the planned track and after the time has elapsed the pilot having noticed the 40 degree error would revise their heading by 40 degrees and fly a track paralleling the planned track - still 3nm to the right.

In example 2, the pilot would first deduce the error and turn by 40 degrees to parallel track. Then they would apply the SCA which would move the aircraft 3nm left of the current track - which happens to be where the planned track is.

Try it both ways on a piece of paper - unless the TMG is paralleling the planned track it is simply a mathematical imposibility to get back onto the planned track.......if for no other reson than there is no right angle triangle!!!

The procedure is good and sound if operated correctly.

jb5000
11th Nov 2009, 17:11
Basically what I think you're saying is...

Fly the SCA back towards your track from the 'new' drift-corrected heading rather than the 'old' one that got you off track in the first place?

Why I doubt I ever really noticed the difference:

1) In your example 18 degrees is a huge track error! This translates to only a 1 mile difference.

2) Are you able to judge the 3nm off track so accurately? If it's further away than that your method actually makes things worse.

3) Small instrument errors, slight heading / speed inaccuracies, wind changes etc. all add up as well.

4) 90knots is a fairly sedentary TAS, anything faster and the effect becomes less and less pronounced.

DFC
11th Nov 2009, 18:46
Basically what I think you're saying is...

Fly the SCA back towards your track from the 'new' drift-corrected heading rather than the 'old' one that got you off track in the first place?



Yes.

True that if the errors are small initially then the difference will also be small and that many errors in the system also come into play.

However, in order to be a valid method of "regaining planned track" then it must at least in theory acheive the aim. This is impossible unless the initial error is corrected (the planned track is paralleled) first.

Here are some examples that while extreme, demonstrate the point;

http://i889.photobucket.com/albums/ac100/pprunedfc/SCA1.jpg

The first example is where the error is 40 degrees - the resultant of applying SCA and then track error correction is that the aircraft parallels the planned track throughout.

The second example (even more extreme) shows that the SCA track takes the aircraft further away from the planned track.

However:

http://i889.photobucket.com/albums/ac100/pprunedfc/SCA2.jpg

The above example shows that even taken to the absurd (but not unheard of!!) error of 120 degrees, correcting the track error and then applying the SCA will always bring the aircraft back onto the planned track.

So fix the error and then SCA back to planned track is a valid use of SCA to regain planned track while apply SCA to the track being flown in error followed by correcting the track error will never do better than a small error and could make the error worse.

I am not suggesting a major change - just a simple change to how SCA is being used which makes it 100% work. The only thing that needs to be changed is the sequence of actions - which make it foolproof (in theory)!

what next
11th Nov 2009, 18:49
Hello!

Are you able to judge the 3nm off track so accurately?I always wondered (same with the rule of sixty): If people are able to determine their track error with such precision, why did they get off track in the first place?

To me, all these methods seem purely academic anyway, especially in the year 2009 (soon 2010!). I rather train my students during their all-too-short and outrageously expensive (at least in my part of the world) flying lessons in state of the art navigation methods that will enable them to stay on their intended track all the time.

Greetings,
Max

DFC
11th Nov 2009, 19:53
what next,

I see that I am overhead X when I should be overhead Y. The map tells me that;

a) From the pre-drawn drift line the track error is ... and

b) the distance from X to Y is ........

More importantly the place to teach navigation is on the ground. The place to practice well understood and used techniques is in the air.

However, as I said at the start this is not a debate about methods. This is about using SCA in a way that will work rather than having to rely on the error being within a very limited rage in order to get almost back onto the planned track.

Please feel free to start another thread telling us about your methods that kep flights on track. You can include the method you use to (once clear of the airspace) return to planned track when ATC clear you to leave the zone on a track that is 120 degrees different from what you expected - refer to the above diagram for the SCA method. I would be interested in your methods that don't inlcude GPS as a sole source of the information. :)

Dan Winterland
12th Nov 2009, 00:06
No DFC, I think it's you who is missing the point. The whole point of the SCA is that it's quick and easy to use. You seem to be transforming it into your next thesis. Navigation can be made simple and pilots like me like simple. The way the RAF teach navigation is that you should be on track as much as possible and if you are off track, you should either fly to a feature on track you can see, of if you can't see one - use the SCA.

But to try and explain how the SCA should really work, look at the following diagrams, for which I didn't use a computer as I'm not that clever - I used a Tucano nav plotter which is set for a speed of 240knots. These diagrams are drawn as accurately as I could - which is probably more accurate than I can fly!

http://i210.photobucket.com/albums/bb73/dbchippy/sca.jpg

In the left hand diagram, the pilot sets off on a track of 360. He has chosen a good check point at 4 minutes, a mast with good vertical profile which he thinks he will be able to see and he can fly to if he's off track. However, he's made the mistake of believing the met man when he said there was no wind, when there's actually a wind of 270 at 60. Getting clost to his mast, he can't see it because it's into sun, so he can't use the ''fly to a feature'' technique. At 4 minutes he sees it to the left at what he estimates is a range of 4 miles. His brain goes into action and he realises that

a) he must get back on track and....

b) he's got to do something about maintaining track when back on.

He activates the SCA part of his brain which has already been programmed that flying at 240 knots, 240 divided by 60 equals 4 miles a minute, 60 divided by 4 is 15 and therefore 15 degrees is his SCA. (He doesn't have to do the maths in the air, he already knows the SCA for his speed). So, he decides to change his heading 15 degrees for 4 minutes, (one minute on the heading for as many miles you are off track) and he will fly this heading of 345 until the stopwatch gets to 8 minutes.

Now he's turned, he wonders what sent him off track. Was it a cumulative error or was it a once only error? He noticed he was drifting quite a lot, so he decided it's cumulative caused by believing the met man. He does a quick calculation and work out that after 16 miles he was 4 miles off track, and that equates to about 15 degrees of error. So he makes a decision that he will change his heading to 330 until 8 minutes and at 8 minutes he will fly heading 345. He flys this accurately and as you can see, he is almost on track. Not exactly on track, but will certainly be able to see his waypoint at 10 minutes.



In the right hand diagram, the pilot encounters weather at 2 minutes. He's flown to the right of track, but he doesnt know how far until he sees the mast to his left at what he estimates to be about four miles. The SCA training kicks in and he applies a heading of 345 which he will hold until 8 minutes. He then decides whether it's a cumulative or a once only error. he knows he got off track avoiding weather, therefore it's a once only error, so there is no additional correction to add.



It's not perfect, but it's the best there is in the circumstances. Errors include the fact that the trigonmetry of the SCA based on the 1 in 60 rule isn't exact, the groundspeed may not exactly be divisble by 60, the distance off track can only be estimated and that there is usually a short delay while mental gymnastics take place - for example, the pilot in case A above will have spent a bit of time on the heading of 345 before deciding he should really be on 330. But, the point is that the pilot will end up close enough to track to identify and fly to his next turning point.

SCA sounds complex at first, but the beauty is that it's quick and easy to use once you have had a bit of practice at it - and it doesn't require a visual feature on track to fly to.

As I said, I've used it all my career while flying visual navigation and it works well in practice.

DFC
12th Nov 2009, 09:22
Dan,

First you have not followed the sequence used by BEagle and many others when teaching SCA. Therefore, you lie somewhere between. However, as can be seen from the following diagram where I have accurately drawn your example a simple change in how you think of what your are doing will

1. Improve the accuracy; and

2. Show that the method has at least the potential to get you exactly back on track - provided the correct actions are taken.

http://i889.photobucket.com/albums/ac100/pprunedfc/sca3.jpg

On the left is your example drawn accurately;

A is the start point - B is the point where you apply the SCA.
C is the point 1 minute later where you decide the track error and apply that also.
D is where you are when you think that you are back on track.

Note that in your example the SCA has not taken the aircraft back towards planned track (since B to C is paralleling the planned track). It is only through application of the wind correction that the aircraft starts closing with the planned track. How confusing is that to a student ( the standard closing angle does not close with anything)?

To the right is the exact same scenario using the sequence I am talking about;

A is the strat point - B is the point where the track error is corrected.
C is the point 1 minute later where the SCA is applied [B]for 4 minutes
D is where you are back on track - and had you done as I say you would be exacly back on track!!

SCA does dork very well if it is done properly.

Both examples would suffer equally because the leg back towards track is more into wind thus - your example would be more off track that shown and my method would be slightly off track.

The circles approximate the minimum visibility possible for VFR in class G. (they are 0.9nm radius which is a little generous!!)

I am not seeking to reinvent SCA or do something that you are not already doing.

You applied SCA then MDR (drift correction).

I am saying that MDR (drift correction) followed by SCA is more accurate, involved the same actions by the pilot (but in different order) and can in theory actually work whereas SCA first can never.

Looking at your righthand diagram. The reason why SCA works perfectly in that example is because the TMG is paralleling the planned track when SCA is applied - exactly what I am talking about.

I don't know why your friend flying in Australia does not know how far off track they are having avoided the weather. Had the used SCA to move the required number of nm right of track to clear the wx then (all being well), they would apply the same SCA to get back to track.

SCA sounds complex at first, but the beauty is that it's quick and easy to use once you have had a bit of practice at it - and it doesn't require a visual feature on track to fly to.SCA is not complex. How easy is it to check the drift line, kill the drift and then SCA for the required number of minutes back to track. - Very.

Your "fly to a feature on track" system is indeed valid - provided that it is not repeated again and again. In other words - look out, see the mast, fly to the mast and when there fly the correct heading - the one that would have taken you to the mast with no error. To do that the pilot still has to be able to determine the drift and MDR the correct heading. Otherwise it is track crawling.

In sumary, I am not adding or removing anything from what you describe. I am merely changing the order of actions to make the resuly more accurate and the method valid as a "get you back on track" method.

Get the idea?

DFC
12th Nov 2009, 09:56
Dan,

To clarify a little further I have changed your scenario slightly.

In this case, the Met man has told the pilot that the wind is 090 at 60 and the pilot has planned based on that. It turns out that the wind is calm. Let's see what your pilot does;

http://i889.photobucket.com/albums/ac100/pprunedfc/sca4.jpg

The left example follows your use of the SCA.

Pilot Departs A. At B they discover that they are off track and apply the SCA. The think about it and decide that the Metman was wrong and there is no wind so the heading to fly the planned track is 000. So they do not change the SCA heading further. Unfortunately, after the SCA time is up they are no closer to planned track than they were at B!!

Following what I say (right diagram) - pilot determines that metman was wrong and there is no wind so they fly 360 becuase that is the heading they should have flown since A and it kills the drift. They then apply SCA for 4 minutes because they are 4nm off track and hey presto they are exactly back on track.

So SCA and then drift correction does not work in this case.

Can we not use a SCA procedure that will work and not just in certain cases?

Ask yourself why the right hand diagram is the exact same in both cases while the diagram of your system (the left one) changes?

BEagle is being very quiet. Will be stride in and put us both right? :)

Dan Winterland
12th Nov 2009, 10:31
Yes, I can see what you are getting at. However, although I didn't allow any time to re calculate the drift after applying the SCA and therfore that would have put me off track, I see you have allowed one whole minute, which puts you over a mile off track at the conclusion of 4 minutes. The drift calcualtion in real life should take less than that - I would reckon more than 15 seconds is excessive so it would happen in less than a mile. This would put you about a quarter of a mile off track which in the scheme of things is nothing when you are trying to find your next turning point. And my example of an extra 60 knots drift is excessive - I used that figure to keep the maths easy and to illustrate the point. If the wind is more than 15 knots more than planned, I would say that was unusual. This would make the error 1/16th of a mile at most.

I was telling you how it's taught at the RAF Flying Training Schools. I'm not too concerned how to refine the technique for my own use as I don't do much of this sort of navigation these days. Most of my navigation is now done by a triple IRS with GPS updates and with my feet on the footrests while reading the newspaper and drinking coffee! And I doubt the RAF are going to change their technique to include a second change of heading to make the track correction extremely accurate in the case of a cumulative error. That would make the tecnique too complex for the environment it was designed for.

When your at low level in turbulence so that you can't read the map properly and you're contour flying and looing out for other aircraft which may be trying to bounce you, the KISS (Keep It Simple Stupid) principle is a good one.

You have to remember that ther are a lot of variables in navigation, especailly at low level. Are you flying the exact speed? Have you recalculated the drift correctly? have you assessed your track error correctly? When you take all these into account, you will see there is a heavy element of the TLAR (That Looks About Right) technique involved.

The level of accuracy you advocate just doesn't happen in real life.

Dan Winterland
12th Nov 2009, 11:37
DFC - replying to your post at 11.56.

Your case A hasn't applied a correction. He should have realised that the error is a cumulative one and a correction to get back on track as well as the heading correction is applicable. He should fly 345 for 4 minutes then correct to 360.

Just like your case B has!

In all cases the SCA will get you back on track, but if it's a cululative error such as an incorrectly applied drift, that has error has to be corrected as well.







I doubt BEagle will say much different to me when he comes back on. He learned the SCA at the same place a me, we were on the same Squadron and later he was the CFI of the flying club I instructed at.

BEagle
12th Nov 2009, 12:00
Agreed, Dan.

1. You find yourself off-track, despite having flown your calculated heading and speed as accurately as you thought possible.
2. Turn towards track by the SCA - do not re-synch the DI at this stage.
3. Whilst puttering back towards track, re-assess the original distance off - was it 3 or 4 miles? Make a note of the drift angle.
4. When time is up, turn onto original heading.
5. THEN re-synch DI, double check rudder trim or ball deflexion.
6. If DI and ball were spot on, error must have been wind. So apply whatever the drift angle was.
7. Amend ETA for any SCA of more than about 30 deg.
8. K.I.S.S

It might not get you back within .035 miles :hmm: of track, but it will enable you to identify your visual fix points more easily.

AND IT WORKS JUST FINE!!

DFC
12th Nov 2009, 13:18
3. Whilst puttering back towards track,.......


Problem is (as can be seen from several of the above diagrams) - you may not be "puttering back towards track"!!!!!

To use the most recent example;

1. You find yourself off-track, despite having flown your calculated heading and speed as accurately as you thought possible.

No problem so far
2. Turn towards track by the SCA - do not re-synch the DI at this stage.

a left 15 degrrees turn in the above examples

3. Whilst puttering back towards track, re-assess the original distance off - was it 3 or 4 miles? Make a note of the drift angle.

Problem - you are not "puttering back towards track - you are paralleling the planed track

4. When time is up, turn onto original heading.

And start diverging in the same way as before having got no closer to planned track

5. THEN re-synch DI, double check rudder trim or ball deflexion.

OK - DI out by 15 degrees. Turn onto correct heading and now parallel track - further off then when the arror was first noticed.

6. If DI and ball were spot on, error must have been wind. So apply whatever the drift angle was.

OK so the DI is spot on and we now turn 15 degrees into wind. We parallel the planned track still further away than when we discovered the problem!!![B]

7. Amend ETA for any SCA of more than about 30 deg.

[B] You are never going to get to the fixc so there is no ETA!!!

8. K.I.S.S

Is that KISS?

Here is a picture of what you describe as KISS. I have copied your numbered instructions to the appropriate points so that there is no confusion as to what happens when we do exactly as you say;

http://i889.photobucket.com/albums/ac100/pprunedfc/beaglescakiss.jpg


I again ask the question is your KISS method doing what it is expected to do? The picture above says no!

Why not simply;

1. check the track error (drift line)

2. Turn by track error

3. Assess miles off.

3. Turn by SCA and hold for required minutes

4 Turn by SCA in the opposite direction.

Now that is KISS

DFC
12th Nov 2009, 13:55
I think we have to go back to basics;

SCA works on the approximate application of SIN / COS in a right angle triangle.

http://i889.photobucket.com/albums/ac100/pprunedfc/SCABasics.jpg

In the left diagram, A - B is parallel to C - D. The triangle formed by a line crossing the two lines will be a right angle triangle.

In the right diagram, the lines are not parallel. Just like in navigation where we are diverging from the planned track.

The triangle formed will not be a right angle triangle.

Thus SCA (which is based on a right angled triangle) will never work when the lines are diverging. It is a mathematical imposibility.

So are we asking the student to (as well as everything else) decide if the error is big or small?, going to leave us with a big or small (or even bigger than we started with) error after using SCA.

That is not KISS.

groundfloor
12th Nov 2009, 15:04
Whew! Learnt the academic 1 in 60 rule which was used for basic flying training - worked like a charm!

When arriving at a checkpoint selected at distance gone that divided into 60 reasonably easily - 15 20 30 - mapread to see the distance off track left or right. So 1Nm off to the right at 30Nm tracking 2deg right. 1 Nm right at 15Nm tracking 4deg right.

Then a corrective turn (double drift) to regain track in the same amount of time to the checkpoint from your set heading point, followed by a turn back onto track with a heading adjusted for the drift experienced to the first checkpoint.

Went something like this (20 Nm Point with 10 min elapsed). " I pinpoint myself on the river between Newcastle and the railway bridge, I should have been 3 miles left of the bridge, I am 5 miles left of the bridge, therefore i am 2 miles left of track which means I have drifted 6 deg left. My heading was 070 deg therefore I will steer 082 deg for 10min and then 076 deg.

Its independant of groundspeed and works

For Nav test purposes this had to be achieved before halfway on every leg.

In the real world - turn onto heading - pick a point on the horizon and fly to it.

Dan Winterland
12th Nov 2009, 15:09
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.

DFC
12th Nov 2009, 17:09
In each case, your track error is the same as the correction so you end up paralleing track


You will find that it was you that chose the 15 degree error and 240 Kt GS (15 degree SCA). :)

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.

-------

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.

groundfloor
12th Nov 2009, 17:46
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.:p

hugh flung_dung
12th Nov 2009, 21:19
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

Dan Winterland
12th Nov 2009, 23:53
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!

BEagle
13th Nov 2009, 06:58
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....:rolleyes:), 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.....;)

Cows getting bigger
13th Nov 2009, 07:50
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).

DFC
13th Nov 2009, 09:13
HFD,


There's no doubt that you are geometrically correct that modifying the SCA by the estimated track error will give a more accurate result.


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.

---------

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.



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.

BEagle
13th Nov 2009, 10:09
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.

DFC
13th Nov 2009, 10:49
it works


Not the way you describe? :)

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. :ok:

BEagle
13th Nov 2009, 10:59
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......:ooh: ;)

Dan Winterland
13th Nov 2009, 14:35
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.

BEagle
13th Nov 2009, 20:14
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..:ok:!

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!

DFC
13th Nov 2009, 21:01
Dan,

60knts = 60 degrees

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. :}

BEagle
13th Nov 2009, 21:26
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.

Dan Winterland
13th Nov 2009, 23:52
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:

http://i210.photobucket.com/albums/bb73/dbchippy/image019.gif


http://i210.photobucket.com/albums/bb73/dbchippy/7432fig06.jpg

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.

Cows getting bigger
14th Nov 2009, 05:57
Dan, your picture paints a thousand words. it would appear that your aircraft is flying a track parallel to the desired track before applying SCA. DFC is right.

BEagle
14th Nov 2009, 07:03
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.

DFC
14th Nov 2009, 08:37
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?

---------

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?

DFC
14th Nov 2009, 08:59
BEagle,


Why wouldn't the heading being flown be parallel to the pre-planned heading for the leg?


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.

-------

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.

Cows getting bigger
14th Nov 2009, 16:32
Beagle, don't shout me down. I didn't talk about headings, I talked about tracks. Now please go away and read the last couple of pages before adopting such a patronising manner.

Dan Winterland
15th Nov 2009, 03:32
There's quite alot of roundabout chat on this thread which is making a very simple technique seem very difficult.

The AP3456 diagram show a parallel track for clarity and to explain the piont. If it's a once only error, such as weather avoid or flying around a hill (quite likely at low level where flying a constant heading and speed isn't always possible) ending up parallel to track is a very real possiblility and then a correction to your original heading won't be necessary. If the track displacement is due to wind then it's a cumulative error, the track won't be parallel and a correction should be made.

AP3456 says apply the SCA and then when it is estimated you have regained track then correct the error. This is OK for fast jets doing 7 miles a minute because your SCA is only 8 degrees and your max drift next to nothing. But it also mentions the technique may be adapted, so there's nothing to stop you making the correction earlier if you wish. I seem to remember that instructing on the Chipmunk (16 years ago now, so a dim memory) we made the turn and while we were heading back to track, we then made an assessment of the drift and applied a correction. (I think I explained this in the post with my hand drawn diagram). No need for clever maths, I don't know anyone smart enough who can do precise trigonometry in their head while flying accurately and looking out - I certainly can't. We often used to make a sensible guess which once we were experienced, got quicker and more accurate. The TLAR (That Looks About Right) method is more than adequate for getting close enough to track to find your next turning point.

One other mentioned adaptaion is to halve the angle at lower speeds and double the time. This is what I used in the flying club environment using 20 degrees for approx 90 knots of GS. I know it can change with GS and quite considerably if the speed is reuced by a srtong headwind, but the point is that it's only going to get you approximately on track so that you will be in visual contact with your next turing point.

SCA is a derivation of the 1 in 60 rule which many track regaining techniques are based on. However, as it uses fixed figures, it's a lot easier to apply and a lot less difficult to screw up. this is why the CAA were advocating the SCA as the futre track regaining tool for GA about 8 years ago IIRC.

It seems the teaching of it in practice may be ''less than effective''. Perhaps it's time for the CAA to issue some guidance becasue there seems to be a lot of confusion.

Dan Winterland
15th Nov 2009, 03:47
DFC wrote:

"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)."

Read the last sentence of the AP3456 extract again. It says:

"When it is estimated that track has been regained, alter heading to maintain the original track (allowing for any change in wind, if necessary)."

DFC
15th Nov 2009, 08:50
There's quite alot of roundabout chat on this thread which is making a very simple technique seem very difficult.



Quite correct. Do what the RAF and I say and it is very simple as well as working correctly.

Look at the diagram, SCA is noted in two places. This can only happen when the track being flown and the planned track are parallel.


"When it is estimated that track has been regained, alter heading to maintain the original track (allowing for any change in wind, if necessary)."


The RAF are using the method exactly as per the diagram. However, at the speeds they fly, the point where the aircraft is estimated to be back on track is perhaps some 7nm away (420Kt GS) from the point in the diagram where the aircraft is paralleling track. As everyone knows, at low level the wind 7nm further down the route can be different. Therefore, having regained track if a different wind exists than existed when the aircraft started the SCA (dotted line in your copy of the RAF manual) the heading to maintain track will be different from that which was used to fly the parallel track - as per the diagram.

Your ascertion that the RAF must be right is correct. The RAF and I are teaching the exact same SCA method with the exact same diagram.

Please re-visit the basics (as per the RAF since you like what they say). SCA is based on the 1 in 60 rule. The SCA angle is measured at the point that the aircraft regains the planned track.

If you can just at least grasp that basic principle from the RAF diagram then you can see that and aircraft with an SCA of 40 degrees diverging from track by 2 degrees will have to turn through 42 degrees in order for the intercept angle (SCA) measured at the point where the aircraft regains track to be 40 degrees.

Can that really be so difficult?

BEagle says turn through 40 degrees and then when back on track...... Even if that does intercept planned track the angle between the intercept track and the planned track will not be 40 degrees - not SCA. Therfore it is not as per the RAF diagram.

All I am saying (have been saying from the start) is that we have to use the RAF method correctly.

I break the 42 degree turn above into two simple steps for the student. Turn by 2 degrees to parallel and then turn by SCA 40 degrees to get back on planned track. The angle betweent he the intercept and planned tracks will be SCA - as per the RAF diagram.

A picture may paint 1000 words.

However the proof of the pudding is in the fact that BEagle's student who ended up in the situation way back in post 18 would fail their GST by following BEagles system. That would not happen of they used the SCA technique correctly.

So I end with the request I made at the very start. If instructors are going to teach SCA as a method. Please teach it correctly so that in practice it is a valid method and will not let the user down.

BEagle
15th Nov 2009, 09:27
This is getting boring....

The system works, don't confuse everyone with your absurd hobby-horse sums.

If the student has calculated a heading of 080, sets off on 080 and maintains a diligent FREDA check cycle to resunch the DI, he/she will have been flying the same indicated heading as planned. Simple.

If a track error is discovered, start the SCA process and get back towards track. Then apply the drift error if, and only if, you are 100% certain of the cause being wind velocity.

If the student has been less than careful with heading maintnenance, the track error might be due to drift or it might be due to an incorrectly set DI or flying out of balance. Reduce the track error first by using SCA (e.g. turn left onto an indicated 040 for 3 minutes if 3 miles right of track, then back onto an indicated 080, then resynch the DI if necessary and, if the DI was OK, apply the drift error. And add 1 minute to the ETA.)

I resent your arrogant comment that anyone using SCA as I've described would 'fail their GST(sic)'. There is no navigation element in a GST - that is an NPPL term. The PPL Skill Test does include a navigation element; all the students I tested who found themselves off track and who applied SCA correctly completed their navigation element well within the tolerances. Not due to luck, but due to diligent application of a very simple technique.

Dan Winterland
15th Nov 2009, 11:13
At 420 knots, we didn't bother with drift much, if at all - not when your max drift is a 7th of the windspeed. In the Hawk, you just pointed the pitot probe where you wanted to go, and usually that's where you ended up.

As for making a correction of 2 degrees before applying the SCA - how are you going to judge that a 2 degree correction is what's required? At 90 knots that's equivalent to 3 knots increased wind component!

If you can judge that at 2000', you're a far better pilot than anyone else I've ever flown with.

DFC
15th Nov 2009, 11:44
If the student has calculated a heading of 080, sets off on 080 and maintains a diligent FREDA check cycle to resunch the DI, he/she will have been flying the same indicated heading as planned. Simple.



But in the real world the wind is seldom exactly as forecast.

The comapss seldom is exactly aligned on every heading and the DI plus compass in most aircraft are graduated in 5 degree steps. Therefore, despite perfect planning calcuations, it is unlikely that even the best pilot will stay exactly on planned track due to the wind being slightly different, the OAT being slightly different (TAS different), the altitude flown not exactly the altitude planned, the QNH not being exactly what was planned, the pilot reading 102 off the compass when it says 101 and setting 103 on the DI when trying to set 102 but of course the actual HDG(M) is 100 - there is a 3 degree error straight away!!!

For short legs, the difference may be minimal. However, are we limiting the future pilot to only flying short legs in excellent visibility?

We teach - fly a constant heading. The whole basis of the common techniques for regaining track is dependent on the heading being constant. If the student wanders all over the place in heading then even if they do manage to fix their position and get back on track they have no idea why they were off planned track.

Being told that if they do everything correctly they will nto be off track does not help.

Will you ever read what you have written and how a student following your instructions can end up more of track than they were at the point they discovered the error - post 18 clearly shows that. Such a student will fail their skill test simply because they did what you said. A PPL could infringe airspace by doing what you say.

Simply put following your steps exactly needs to have a health warning because no method of correcting back onto track should ever in any circumstance cause the pilot to be more off track at the end than they were when they discovered the error.

-------

Dan,


As for making a correction of 2 degrees before applying the SCA - how are you going to judge that a 2 degree correction is what's required?


Another joke? :)

I seriously hope so.

I made the error so small because BEagle complained that I was using errors that were too big in relation to the SCA. I could have used 1 degree error with an SCA of 40 degrees. The result would still be that in order for the intercept angle at the planned track to be SCA (40 degrees) the diverging track would have to change by 41 degrees.

To answer your question;


how are you going to judge that a 2 degree correction is what's required?


The first student I asked came up with the correct response;

Because having held a constant heading, after 30 miles you are 1nm off planned track.

Simple indeed.

BEagle
15th Nov 2009, 12:25
Will you ever read what you have written and how a student following your instructions can end up more of track than they were at the point they discovered the error - post 18 clearly shows that. Such a student will fail their skill test simply because they did what you said. A PPL could infringe airspace by doing what you say.

Simply put following your steps exactly needs to have a health warning because no method of correcting back onto track should ever in any circumstance cause the pilot to be more off track at the end than they were when they discovered the error.


Complete and utter drivel. You're trying to use an absurdly extreme case to justify your pointless mathematics.

Even with a DI and compass aligned on a northerly heading on a bumpy day, I've never seen such huge errors as your diagrams portrayed. In any case, the student will (if he/she's been taught correctly) have pre-planned sufficient visual fixes to ensure that the time between them is no more than about 10 min in still-air, so correcting exactly back to track after SCA correction will be simple.

When I've flown the aeroplane to a position deliberately off track and handed control to the student to practise an SCA correction, at the end of the correction I've revealed the GPS CDI to them to show them how close they are to the pre-planned track. It was usually exactly in the centre, even with the CDI set to ± 1.0 nm full scale deflexion.

HQ CFS agree with my teaching - if you don't accept it, take it up with them. As Dan and I have repeatedly told you, SCA applied exactly as I've described works just fine.

Lastly, any more insulting remarks alleging that people to whom I've taught SCA will be likely to fail their Skill Test will not be tolerated. You may have your opinion on the matter, misguided though I think it is, but blatant accusations are wholly unacceptable.

DFC
15th Nov 2009, 17:52
You're trying to use an absurdly extreme case to justify your pointless mathematics.



Am I? Is being 1nm off track with a 2 degree error absurdly extreme? I can use 1 degree as the error and 0.1nm off track to show that you are not teaching SCA as described by the RAF!!

You pick the figures (any ones you like) and I will show that what you describe is not the RAF method.


Lastly, any more insulting remarks alleging that people to whom I've taught SCA will be likely to fail their Skill Test will not be tolerated. You may have your opinion on the matter, misguided though I think it is, but blatant accusations are wholly unacceptable.


A candidate who uses a method of track correction that can cause the aircraft to be further off track at the end of the correction than they were at the start will fail their skill test. That statement is true no matter what they use as a method.

It would only be insulting / unacceptable if the comments were both untrue (post 18 shows otherwise) and referred to something which was your invention and personal method (which you claim it is not). :)

Remember that the RAF measure SCA at the point where the aircraft intercepts planned track. You don't and there is the crux of the problem. If you did we would not be having this debate.

Please Please look at the RAF diagram.

If the RAF approve your teaching of SCA then they need to change their AP as quoted by Dan above. I don't think that is likely! :D

The health waring stands until you can show that what is shown in post 18 is impossible, I have mis-used your description of how to apply SCA with the figures supplied by Dan or you can show that by using another common method (1 in 60, double the error, etc) the same thing would happen.

Big Pistons Forever
15th Nov 2009, 18:04
This thread started out interesting but has now IMO just become silly. The point of the exercise is to get to the destination, not apply mathematical formulas to the 2nd ddecimal point. If we are talking PPL training than three most important things things students must do are

1) learn how to fly a steady heading for a substantial period of time (harder to do then it sounds for new pilots)

2) At any time in the flight be able to point to the map and say "this is where we are"

3) Understand and apply the basic SCA concepts which are you must calculate a heading to maintain and then a heading to regain. After this the student must be able to apply the TLAR (That looks about right) test ( ie have we turned in the right direction and is the magnitude of the course change to regain, sensible)

My experience, particualarly at the PPL level, is that the method by BEagle in the first post of this thread is plenty good enough to do the job of getting to the destination. While you can point out the theoretical limitations of this explanation and rightly point out that strickly speaking it is not completely mathematically correct, in the real world of PPL's flying light aircraft it just doesn't matter.

Cows getting bigger
15th Nov 2009, 19:05
Hence the reason many instructors don't bother teaching SCA. There are far simpler methods of regaining planned track. It would appear however, that there are some who can't see the wood for the trees. :)

BEagle
15th Nov 2009, 19:31
The main reason why some instructors are unable to teach SCA with confidence is because they weren't taught it themselves, have minimal real world experience, can't find any reference to it in their Janet-and-John instructor notes and don't really understand the elegant simplicity of the method.

Listen to the wise words of Big Pistons Forever, a chap with vastly more experience than most others on this site.

DFC
15th Nov 2009, 19:57
Understand and apply the basic SCA concepts which are you must calculate a heading to maintain and then a heading to regain.


Exactly.


Listen to the wise words of Big Pistons Forever


Indeed :D :D :D

---------

As I said at the start I don't want this to be a for / against SCA debate.

SCA when properly applied is a simple effective and appropriate method of both regaining track and moving the aircraft a set distance left or right of current track.

It not the only method but I do agree with BEagle that it is a simple method.

Dan Winterland
15th Nov 2009, 22:57
"As for making a correction of 2 degrees before applying the SCA - how are you going to judge that a 2 degree correction is what's required?

Another joke?

I seriously hope so".

Yes, you're absolutely correct. What was I thinking?. If you look at the video below which I just posted on You Tube, at about 1'.12'' you will notice we applied a 2 degree track correction.

YouTube - Tucano Low Level (http://www.youtube.com/watch?v=2wR7NqgUcfM)

DFC
16th Nov 2009, 09:20
Dan,

We are talking about DR techniques as applied to the civil pilot here. Your video is of low level military exercise with legs measured in seconds rather than minutes.

Do you teach civil pilots to operate their normal navigation exercises at such levels with such short legs?

You have shown us the RAF book answer is the same as what I have been trying to get across. Please do as BEagle says;

Quote:

Originally Posted by BEagle
Listen to the wise words of Big Pistons Forever


Quote:
Originally Posted by Big Pistons Forever
Understand and apply the basic SCA concepts which are you must calculate a heading to maintain and then a heading to regain.

Exactly. :ok::ok::ok:

Dan Winterland
16th Nov 2009, 12:21
FERFECKSAKE! Don't you have a sense of humour? Don't you understand Irony?? Of course we wern't flying 10 second legs. And how do you think we were going to map read accurately in all that turbulence pulling 3g round the corners? I couldn't even see the map! The whole point of posting the video wasn't to show how good military pilots are (although I thought we looked pretty cool) it was to demonstrate that the subject of navigation has many aspects and should be flexible.

The point is that navigation is sometimes more of an art more than a science. You can talk about the theory all you want, but in the end it's all about common sense and how you apply the techniques to achieve the aim. Often it's difficult. But there are tricks of the trade which will make it easier, whether you're doing 420 knots at 250', or 90 knots at 2000'. And the SCA is one of those.

The theory of SCA is simple. It's application is even easier and the results more than adequate to achieve the aim of finding the next turning point or the destintion. But it's use (as with any navigation technique) does require some flexibility and intelligence. Put those together and they equal common sense (which is what I understood what Big Pistons Forever was trying to say in his last post).



Something which seems to be lacking in this discussion.

BEagle
16th Nov 2009, 13:37
Exactly, Dan

Now, are you sure it wasn't 3.035 G?

I remember the Ladybower run! But in those days it was in a JP5 - and the fun detectors had a 500ft MSD limit in place....:mad:

Do you see any differences between 'my' SCA teaching and that taught by CFS? Apart, that is, from the timing correction when using a 40 deg SCA.

Amazing how all our students managed quite happily, isn't it? In fact the only student I recall failing the navigation section of his Skill Test was someone who over-read his chart, misidentified a town and started flying in circles trying to work out where he was..... Yet there was a 'dogs nuts' feature nearby, from which an SCA correction would have been easy.

He'd been 'taught' some other method by a 'double error dinosaur'; when he was retaught using SCA he passed with ease.....:rolleyes:

DFC
16th Nov 2009, 15:29
Do you see any differences between 'my' SCA teaching and that taught by CFS?


Where do you want me to start? :rolleyes:

However, in the interests of safety, I am obliged to point out that someone doing it your way could possibly end up infringing airspace because that is a definite posibility that exists with "your way" and no other way.

Anyone who sits down and says that when flying at 1nm per minute it will take you 1 minute to travel a distance that is greather than than 1nm should not be involved with navigation.

To expect a customer to pay for being told such rubbish is unbelieveable.

I have tried as much as any instructor can ever be asked to try and teach you something - to mend the one problem with your procedure by a simple tweek. You refuse to take-in what is being said most probably because you feel it is a personal afront to say that something you have devised does not work.

Perhaps the FIE doing your next renewal will take some time to discuss the issues. :E

Until then, the health warning must stand that a pilot following your method could end up more off the planned track than they were at the start of the "correction". They could as a result infringe airspace, fail their test or find that they have less of a safety margin against terrain than they planned.

BEagle
16th Nov 2009, 16:51
The question was for Dan, not you with your stupid obsessions, DFC.

Big Pistons Forever
17th Nov 2009, 00:17
RE the Tucano video. What I saw was a radio mast used to set a heading untill the inlet became visible and then cranking and banking as necessary to follow the inlet. Jolly good fun and a great piece of practical navigation but I am frankly stuggling to see where SCA was applied.:confused:

Dan Winterland
17th Nov 2009, 01:03
Hi BEagle, no I don't. The point to make is that although the SCA is fixed for your groundspeed, and it should be applied for as many minutes you are miles off track, it's still a flexible technique. You can pick the bits out of it which work best for your situation. Which is what AP3456 says and how I learnt it when I was a student. It's use should be applied with common sense.

Hi BPF. I think the irony of my comment was lost a little. I posted the video to show that navigation not always a black and white science which is what is being advocated on this thread. The route was one I used to give the students when running up to their Final Handling Tests at an RAF flying training school. They had to do about 10 minutes low level navigation before all the GH stuff. The route took them from Nottingham in the UK, west to Buxton which is in the peak district, north to the TV mast at Crossland Moor and then south down Ladybower resevoir. It was a good route as it was quite tricky with airspace all around (at the mast, Manchester TMA is only 2000' above you) and some great contour flying. The test was not about the navigation as that had already been assessed on the Final Nav Test. It was more about the low level handling.

The video is turning at Crossland Moor mast and then weaving down Ladybower. The resevoir has several dams and it was the one used by 617 Sqn when they trained for the Dams raid. The video was shot by me in the front seat with another instructor flying from the back. The day was very bumpy and Chris was flying quite hard, you will notice the g meter was reading 3g in the turns and it was all I could do to hold the camera.

The nav technique being used was following a line feature, so no need to use the SCA as we were always on track - or close to it. Actually. the direct track on the map went about a mile to the East, but by following the line feature we knew we would end up on track eventually. Low level navigation is all about contour flying to give you the best protection from being seen and staying exactly on track not a major consideration. The only time you really need to be on track is on the final run in to a target.

Oktas8
17th Nov 2009, 19:23
Perhaps the FIE doing your next renewal will take some time to discuss the issues.

Nope. (Insert emoticon for wincing at the thought of being so crass.)

But I would very much enjoy the privilege of doing a check for many of the posters here. First five minutes ticking boxes to satisfy CAA criteria, then the following 55 minutes enjoying watching an expert do his job well. Everybody happy.

O8
FIE

Dan Winterland
17th Dec 2009, 14:11
Ditto.

And if you're interested, I've just uploaded two more You Tube clips from the same flight as the low level down Ladybower resevoir video.

YouTube - Tucano Formation.wmv (http://www.youtube.com/watch?v=OQ-QIer3TFA)

YouTube - Tucano Tailchase.wmv (http://www.youtube.com/watch?v=F-2C1mYx6j4)

GearDownFlaps
17th Dec 2009, 15:16
Cracking Videos Dan
I teach sca to students at ppl level primarily because i am a Fxxkwit and cant do any sort of mental maths whatsoever . I have yet to have a student (assuming his wind his correct etc etc ) ever fail to regain track and adjust accordingly using this method .
So im happy with it:ok:

Checkboard
19th Dec 2009, 21:47
Just read the four pages of this, and found it mildly amusing. :) Thanks guys :ok:

It's interesting to see two sides arguing so positively FOR "SCA" - and thus wondering why there is an argument at all!

Having said that, and understanding both sides, have to say I am with DFC on this one - all DFC is trying to say is "SCA is great - just make sure you are pointing the right way before you use it."

I also understand most won't care - but at least DFC can know that yes, it does get read. ;)

DFC
20th Dec 2009, 23:15
all DFC is trying to say is "SCA is great - just make sure you are pointing the right way before you use it."



Exactly.

9 10