Quote 18 greens: "I've nothing against SCA (whichever floats your boat and it works). With the SCA method you need to know how many miles you are off to apply the sca then determine your closing heading , then apply the new track. And how do you know when you have regained track."
1. To find out how many miles off track you are, you refer to your map and estimate. You will probably be within a mile, which means you should see your turning point when you get to it.
2. The closing heading will always be the same. If you've planned at 120 knots, it will be 30 degrees off from your originally planned heading. The amount of time you fly this heading is the variable and this depends on you off track estimate.
3. How do you know when your on track again? You trust the method. You turn back onto your original heading (with a suitable correction if you consider the error to be persistant) when you have reached the time to do so. This will probably be without reference to the map. If you apply the technique accurately, you will be back on track, or certainly close enough to find your next check/turning point.
The technique works. It's simple geometry and what's more, it's very easy to apply. I was learnt the technique while a pilot in the RAF and tought it to my PPL students subsequently. Some of the techniques the students had been taught previously to regain track or fly direct to the TP ranged from the mildly confusing to the completely baffling, and from interesting to astounding. Getting out your nav rule, protractor and whizz wheel while attempting to fly accurately and look out is not a practical option in my opinion. Without exception, those I showed the SCA to agreed that it was the best method by far.