Hello,

in RPL/PPL Volume 2, Part 6 question 52, we must select a feature for the "most accurate speed check between WEE WAA and YSGE".

I went for the Moonie River crossing, since it's around 60 nm from WEE WAA and the map depicts it as large enough to set apart from other features in the area.

However, the correct answer is indicated to be the Gwider Highway crossing, which is an additional ~40 nm flight time.

My thinking for the river is big enough to not miss, and I'd cross it earlier in the flight so I can get an earlier speed check.

I can see good reasons for picking the highway. For example, the river's water may fluctuate over time, making it smaller or large, therefore a variable feature, whereas the highway looks always the same.

Could you help me understand that thinking behind choosing the highway instead of the river in this case?

Thank you!

You're missing the point behind the book's recommendation. I suggest that there is naught wrong with your thought processes.

If you are looking for track guidance, then you are best served by some sort of linear feature which is more or less aligned with your planned track. Perhaps something along the lines of a highway or railway line going in the same direction as the aircraft is ?

If you are looking for a G/S check, then you are best served by some sort of linear feature which lies athwartships of your track. Again, perhaps a highway or railway line which lies approximately at right angles to your track ?

These recommendations are looking at what is likely to be the MOST useful sorts of features.

In your story, there is nothing wrong, per se, with the river. Most of us would use BOTH features to figure G/S as the flight progresses. The question, though, probably is addressing the consideration of which is the BETTER feature. If a text author were to consider all the ifs, buts, and maybes ... the text would end up half a metre thick ....

Thank you, John, that's clarifies it for me.