[aprssig] APRS Speed Spec? (Above Mach 1)

Brett Friermood brett.friermood at gmail.com
Thu Oct 12 10:45:39 EDT 2017

On Thu, Oct 12, 2017 at 8:16 AM, Robert Bruninga <bruninga at usna.edu> wrote:

> These remain in Knots because that is the APRS standard for speed, but of
> course you can also display them in MPH if you want to make that conversion
> which I think all PILOTS use.

In US Aviation, knots is the standard measure of speed. If interacting with
ATC or other aircraft speed needs to be reported in knots, distance in
nautical miles (except weather related distances in statute miles), and
altitude in feet. Using anything else simply doesn't work.

Now there are a number of pilots who use MPH and statute miles inside their
aircraft. Many older aircraft have airspeed indicators calibrated in MPH
vs. knots and there is actually a large number of experimental amateur
built aircraft that were purposefully built with MPH airspeed indicators.
It's really just a personal preference, but any interaction outside the
aircraft still needs to be in knots.

Brett KQ9N
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