"Mike Rapoport" wrote
Thanks, it does. The question of what the red mark on powered
airplanes means remains. Is it Vne at the aircraft's ceiling? If it
is Vne at sea level then there should be some language in the flight
manual warning of this.

Mike... this is from 23.1545

(c) If VNE or VNO vary with altitude, there must be means to indicate to
the pilot the appropriate limitations throughout the operating altitude
range.

(d) Paragraphs (b)(1) through (b)(3) and paragraph (c) of this section do
not apply to aircraft for which a maximum operating speed VMO/MMO is
established under §23.1505(c). For those aircraft there must either be a
maximum allowable airspeed indication showing the variation of VMO/MMO with
altitude or compressibility limitations (as appropriate), or a radial red
line marking for VMO/MMO must be made at lowest value of VMO/MMO
established for any altitude up to the maximum operating altitude for the
airplane.

Bob Moore