On 01/04/2007 04:28 AM, Torsten Dreyer wrote:
> Well - at least on the eastern side of the atlantic, where I do instrument
> flights in real world, the 090 radial is always EAST of the station, the 270
> radial is WEST of the station.
> A controller advice "proceed on radial 090" or "intercept radial 090" always
> means you shall fly exactly east (magnetic) of the station and fly away from
> it.
> If you are requested to fly on radial 090 *inbound*, you are expected to be
> east of the station and fly *to* it on a track of 270.
This is the sort of thing that gives pedantry a bad name.
1) I started this discussion by discussing a number of scenarios
and emphasizing that in most of them, position was specified in
terms of bearing /from/ the reference.
So please let's not argue about specifying pointlike positions and
locations. There is nothing to argue about. The --azimuth option
to fgfs is unconventional, and AFAICT nobody disagrees about that.
2) The exception to the "outbound radial" rule applies not so much
to positions as to course lines.
Pedantically and etymologically, all radials "should" be rays i.e.
half-lines. In contrast course lines are /lines/ (not half-lines).
Operationally, lines are very significant.
If you are west of the station,
-- a controller could (in pedantic theory land) instruct you to
intercept the "090 course line that passes overhead the XYZ VOR";
-- or I suppose another circumlocution might be "intercept the
reciprocal of the XYZ 270 radial";
++ but it is rather more concise to call it the "XYZ 090 radial",
which is the terminology that US controllers use (and are required
to use).
You can think of it as a _generalization_ of the idea of radial if
you like: a radial that is a line rather than a half-line.
I say again that using half-lines /from/ the station is good practice
and common practice for specifying locations. But the point remains
that using full-lines is good practice and verrry common practice for
specifying courses. (The full-line terminology differs from the half-
line terminology only for inbound courses.)
As additional support for this, if any were needed, consider the case
where you are southwest of the station, and instructed to fly a 045
heading to intercept the 090 radial. Depending on the deails of the
situation, you might intercept the relevant line on the near side or
far side of the station. The controller doesn't care -- and you
shouldn't care either -- which of these two cases comes to pass. From
a human-factors point of view it would be bad practice, indeed it
would be absurd to worry about the distinction between these two cases.
For good reason the VOR CDI indicator was designed to conceal the
distinction. These human factors have been understood since at least
the 1940s, when the VOR system was designed.
Bottom line:
-- When specifying pointlike positions, radials are rays i.e. half-lines
radiating /from/ the station.
-- When specifying course lines, radials are full lines.
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