Hey Bob and Team,

This question has been wrecking my brain as I have no idea how to approach it.

An aircraft flies south from 20 degrees South for 600nm, the LMT of EOD at destination will be:

a. Later by 18min on 31st January
b. Later by 19min on 30th June
c. Earlier by 18min on 31st January
d. Earlier by 19min on 31st March

Would really appreciate you help on this one.

Ah, this is a problem only until you twig to where some information exists.

We are talking end of daylight. You normally are concerned more with longitude effects rather than latitude and the latter tends to get overlooked somewhat. However, where do you go to get the information anyway ? Beginning and end of daylight charts - AIP GEN 2.7-3 through -6. Do these give you any information on latitude ? Indeed, they do as one of the parameters involved is latitude.

So, the next consideration is "how far are we flying south" in terms of latitude ? We are flying south (ie along a meridian of longitude), which is a great circle path, so we can use the normal latitude scale conversion of 1 minute latitude = 1 nm (approximately). So, for 600 nm, we have a very simple mental sum

600 nm = 600 minutes of latitude = 10 degrees of latitude

so we are moving from 20S to 30S for the exercise.

Now, it is just a case of testing each of the available answers to find one which works.

(a) GEN 2.7-5 gives you, for 31JAN, around 1907 LMT (20S) and, around 1925 LMT (30S). Difference is 18 minutes later. Looking good ?

(b) GEN 2.7-6 gives you, for 30JUN, around 1755 LMT (20S) and, around 1736 LMT (30S). Difference is 19 minutes earlier. Bin.

(c) we can bin this one by reference to (a). We are looking for a later time, not earlier.

(d) the chart gives a negligible difference so we can bin this option.

So, (a) looks to be the one with which to run for me. It would have been better had the question made it clearer that we are looking to compare EOD for the two latitudes but that is pretty much a logical conclusion.

Thanks so much John ! You're a lifesaver! Will definitely try more questions like these to get a more handle on these type of scenarios.

Will definitely try more questions like these to get a more handle on these type of scenarios.

That's the trick. First, one needs to learn the background stuff. Then it is just practice, practice, practice. The only two things in the exam which present a problem are speed and accuracy.

Did I mention practice, practice, practice ?