Hilton wrote:


Yes, if we all had extremely efficient receivers, but we don't. The FAA and
some radio guys got together and decided on applicable distances. Once they
figured that out, they had a bunch of semi-spheres. While it would have
been 'correct' to define the service volumes are a semi-sphere, it wouldn't
have been all that useful to us (pilots). So the FAA made them (mostly)
cylinders (and ensured that the cylinder lay within the semi-sphere) to make
it easy for pilots to figure out whether or not they were in the service
volume. i.e. it is a combination of radio effectiveness and pilot
usefulness that describes the service volume.

I just made that up, but it sure sounds convincing, logical, and almost as
good as if I had stayed at a Holiday Inn last night... instead of working
on software.

Hilton

If the FAA simply depicted a cylinder of theoretical signal strength
within the actual "semi-sphere" of service, I would completely follow
the analogy.

However, the FAA has depicted cylinders of various diameters stacked
upon each other. Given that the VOR is line-of-sight, I did not
understand why, for example, a VOR would be received 130nm out at FL180
yet only be received 100nm at FL500. Doesn't it logically follow that at
the higher altitude the VOR would be able to be received further out?

(See AIM 1-1-8)and then order some room service! ;-)

Antonio