On 12/31/2008 10:29 AM, I wrote:
> Standard dogma in IFR training is that the VOR CDI indicates
> two degrees per dot, while the LOC CDI indicates half a degree
> per dot. These numbers are quite believable. Good practice
> is to check them as part of the 30-day IFR receiver check.
Important clarification: The VOR numbers are quite believable,
and are checked monthly. However.....
The LOC numbers are only a rough rule of thumb. According to
the AIM, the localizer beam is supposed to be designed to be
700 ft wide at the threshold. That's ±350 feet if you prefer
to think of it that way.
That means that as the runway length varies from (say) 6000 ft
to 15000 ft, the CDI sensitivity varies from more than 0.6
degrees per dot to less than 0.3 degrees per dot. (I hear
rumors that it is artificially pegged at a minimum of 0.3
and a maximum of 0.6, overriding the 700 ft rule, but don't
quote me on that.)
The 0.5 degree dogma will get you in the ballpark, but
that's all.
Quoting from navradio.cxx
// According to Robin Peel, the ILS is 4x more
// sensitive than a vor
r *= 4.0;
That may be useful as a rough approximation, but nothing
beyond that.
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