[Navigation] Variation & Deviation

[Joshilini]

Hello!

I am currently studying for my PPL(a) in the United Kingdom. I have recently bought the "Air Pilot's Manual" series and have been trying to answer the helpful questions at the back of the book.

For the Air Navigation book (book 3), there is one particular question on variation & deviation which has slightly confused me. Here is the question:

Given the following deviation card, fill in the blank spaces in Table 3 below (page 449 for anybody with a copy of this book):

FOR/STEER:
N/003
E/087
S/181
W/272


I filled out the table and it looks like this:

http://i50.tinypic.com/1j9jf8.png

All of my answers were correct apart from the one highlighted in red. According to the book, the answer is actually 022.

My question is... why? :D

Thank-you.

[Air Soul]

Rather than just give you the answer, I'll give you another question!



Give Compass headings for the following True headings, all Var 8W, and Dev as per your original question;

T
090
060
045
030
360

Hope that helps!

KR

AS

[TCL68]

From the Deviation card, track N, steer 003 (3 right) and at E steer 087 (3 left), so there is a difference of 6 degrees right to left. Interpolate and do the maths.
More importantly, for as much as you plan, when in the air, the wind will seldom be as planned, so corrections are necessary. So while good planning is very important, good technique for corrections is paramount.
Good luck with the exam and hope that helps.

[Joshilini]

Thank you Air Soul and TCL68 for your help. I understand how it works now. I have my navigation exam next week.

Thanks again.

[flying_highover]

From the Deviation card, track N, steer 003 (3 right) and at E steer 087 (3 left), so there is a difference of 6 degrees right to left. Interpolate and do the maths.

Interested in this myself.

Could you explain the maths behind it bit further?

Thanks!

[selfin]

Quickest approach for this is linear interpolation (http://en.wikipedia.org/wiki/Linear_interpolation).

Here's a graph depicting the above problem to complement the Wiki article. In this example the 021.67° has been rounded to 022° as most of us, in Britain at least, try to avoid flying decimal degrees.

http://img37.imageshack.us/img37/1281/lerpdev.png