How wide is an NDB approach course?

Within 10deg is pretty simple guidance in my book!

Bill Zaleski wrote:
On Wed, 17 Jan 2007 04:57:04 GMT, Jose
wrote:

[You're established inbound on an NDB]
When within 10 degrees of the published course.
There is no policy or rule to support that.

Taking Sam Spade's TERPs quote,

The primary area is longitudinally centered on the FAC, and is 10 miles long. The primary area is 2.5 miles wide at the facility, and expands uniformly to 6 miles wide at 10 miles from the facility.

I draw a little diagram, and find that the angle along the outside of
the primary area to be atan(((6/2)-(2.5/2))/10) = atan(7/40) = 10
degrees. So, ten degrees from the facility puts me 2.5 miles inside the
protected area. Sounds good to me. Start on down.

Jose

That's a lot of math to try to acomplish during an NDB approach.
Sounds like you are measuring it with a micrometer and cutting it with
an axe. You need much simpler personal guidelines when you take this
stuff into the cockpit.