Originally Posted by
RichardH
An unusual question as it has been asked. Questions with positions on different latitudes usually state that the highest track (or vertex) occurs at a particular longitude.
At the vertex the GCT must be either 270 or 090, then you can use convergency (conversation angle not available) between the given vertex longitude and wherever they want the GCT measured.
Once you have done a couple these are relatively straightforward.
For this question I drew an accurate scaled polar/circle diagram and got GCT at A 190 GCT at B 340, but the diagram is too complicated to show & explain here.
I wouldn't waste too much time on these type of questions, also not sure your source of questions is entirely reliable, been some strange wording along with an incorrect answer before.
Many thanks again Richard. If you wouldn't find following my thoughts a little further: this isn't a question I have found in an ATPL question bank. I am trying to make a ATPL question of my own. But choosing 2 points A and B, I guess the value of the GCT at A and B has a specific value. I can't simply "STATE" that the GCT at B is that much, to then calculate the GCT at A. So I wanted to find the GCT at B to deduce the one at A. I have tried using this webite:
https://onboardintelligence.com/GC.
And I get:
And:
So GCT arrival at B = 340°.
From that I can do my hand calculation and find GCT at A:
________________________
Given GCT(B) = 340°, let’s find the exact GCT(A): We know g° (the difference in longitude) between 110°W and 100°E = 70°+80°=150°.
The Mean Latitude is Lm = 82,5
And we know that: GCTB - GCTA = Cg = 2 CA = g. sin (Lm) = 150°. sin(82,5) = 148,72.
So the GCTA= GCT B - Cg = 340 - 148,72 = 191,28°.
Close enougt to the answer 190° from the website?
Right? Is that acceptable?