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# Teaching SCA as a method

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# Teaching SCA as a method

14th Nov 2009, 16:32

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15th Nov 2009, 03:32

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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.
15th Nov 2009, 03:47

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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)."
15th Nov 2009, 08:50

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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.
15th Nov 2009, 09:27

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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.
15th Nov 2009, 11:13

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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.
15th Nov 2009, 11:44

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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.

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.
15th Nov 2009, 12:25

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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.
15th Nov 2009, 17:52

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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.

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!

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.
15th Nov 2009, 18:04

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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.
15th Nov 2009, 19:05

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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.
15th Nov 2009, 19:31

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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.
15th Nov 2009, 19:57

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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.

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

---------

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.
15th Nov 2009, 22:57

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"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.

16th Nov 2009, 09:20

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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.
16th Nov 2009, 12:21

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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.
16th Nov 2009, 13:37

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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....

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.....
16th Nov 2009, 15:29

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Do you see any differences between 'my' SCA teaching and that taught by CFS?
Where do you want me to start?

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.

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.
16th Nov 2009, 16:51

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The question was for Dan, not you with your stupid obsessions, DFC.
17th Nov 2009, 00:17

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