Topic Author
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Joined: Tue Nov 30, 1999 12:10 pm

What Is An Isochrone?

Mon Jul 28, 2003 11:40 pm

If anyone can help on this one, I would greatly appreciate it.
In preparing for the JAA OPS exam, I have come across this question:

When a course is plotted at minimum time route, one passes from the air isochrone to the corresponding ground isochrone by applying to point K (original spot) a vector KK' which is equal to

wind at K.
wind at K'.
mean wind from the preceding ground isochrone.
mean wind up to the next ground isochrone.

and there seems to be some argument as to the proper answer.

Can anyone help?

Posts: 1278
Joined: Tue Oct 16, 2001 4:05 pm

RE: What Is An Isochrone?

Tue Jul 29, 2003 12:05 am

My attempt for this question:


n : an isogram connecting points at which something occurs or arrives at the same time


A line on a map, chart, or graph connecting points of equal value.

If that's the case, what that means is your air plot and ground plot both have equal specific time values, but are just pointing in different directions with different lengths.

In that case, I'd pick c), because that vector would represent the winds you have already encountered on course since your last position fix.

I could be wrong, because I'm not too terribly familiar with that kind of lingo either.

I thing I am certain about this whole thing, though. Blame the French for coming up with words like these in their exams.
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Joined: Sat Aug 18, 2001 7:10 am

RE: What Is An Isochrone?

Tue Jul 29, 2003 12:24 am

It's just a line on a map. Like an isobar which connects points of equal pressure and isochrone connects points where things happen at the same time. A circle marking the distance in each direction a plane could travel in an hour is an icochrone.
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