Airplane's compass mag dev

[George Las]

Morning

I have to preface this post by telling you that I am not a pilot, nor will ever be due to a physical impairment, but since my senior year in high school (1971) have had a very keen interest in aeronautics.

Now for my question regarding magnetic heading and the aircraft's magnetic deviation.

If I'm not mistaken when "swinging the compass" is performed it is done in 30 degree increments. Right?

Let's us say that after swing the compass it is found that the correction for 060 degrees you would steer 062, and for 090 you would steer 095 degrees.

So in order to find the calculated compass heading what deviation would be used if for example your magnetic heading is 075 degrees?

What I'm basically asking is how to figure the deviation between the 30 degree increments?

Thanks in advance.

George

[Curt Johnson[_2_]]

In theory, interpolate. In your example, steer 078.5 degrees.
In practice, you can't resolve that on the compass, the local magnetic
variance isn't constant, and the winds don't always do what the
forecasters say, so aim for somewhere between 075 and 080 until you see
the next landmark on your route plan.

Curt

On 3/24/2012 7:40 AM, George Las wrote:
> Morning
>
> I have to preface this post by telling you that I am not a pilot, nor
> will ever be due to a physical impairment, but since my senior year in
> high school (1971) have had a very keen interest in aeronautics.
>
> Now for my question regarding magnetic heading and the aircraft's
> magnetic deviation.
>
> If I'm not mistaken when "swinging the compass" is performed it is done
> in 30 degree increments. Right?
>
> Let's us say that after swing the compass it is found that the
> correction for 060 degrees you would steer 062, and for 090 you would
> steer 095 degrees.
>
> So in order to find the calculated compass heading what deviation would
> be used if for example your magnetic heading is 075 degrees?
>
> What I'm basically asking is how to figure the deviation between the 30
> degree increments?
>
> Thanks in advance.
>
> George
>
>
>
>

[Kai Rode]

>So in order to find the calculated compass heading what deviation would
>be used if for example your magnetic heading is 075 degrees?

In theory you should use linear interpolation. In practice no one I know
even bothers. You can't steer that precisely anyways and such precision
would only be useful for dead reckoning...hello NDB/VOR/GPS? But to pass the
test you should know how it's supposed to be done.