"Ben Jackson" wrote in message =
news:YL5xd.284746$R05.189455@attbi_s53...
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I never understood why they bothered to specify a "book" speed for
approach category when the real rule is that it's based on the speed
that you fly during the approach.
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Ben Jackson

The reason is based in aerodynamics.
1.3 Vs0 is an acceptable approximation to the point of maximum
lift/drag ratio of fixed-wing airfoils on typical small =
general-aviation aircraft.
That makes it a reasonable target for threshold-crossing speed.