OK, this makes sense. It is simpler to position the red mark for the most
conservative conditions than to have a varying Vne. In gliders, often used
for racing, it makes sense to provide the pilot with the actual Vne which
varies with altitude so that they can extract maximium performance.

Mike
MU-2



"T o d d P a t t i s t" wrote in message
...
"Mike Rapoport" wrote:

Vne is a fixed mark on the airspeed indicator and,
as such, doesn't move.

Despite the Vne mark on the altimeter, it definitely is not
a fixed IAS (or CAS) number. Nor is it always a fixed TAS
number. It is the number defined by the manufacturer that
is usually found in the flight manual.
Wilbur Wright

So what is the mark on the airspeed indicator supposed to mean then?

Good question. Here's the rule:

FAA Federal Aviation Regulations (FARS, 14 CFR)
23.1545 - Airspeed indicator

(a) Each airspeed indicator must be marked as specified
[including Vne] ...

(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.

I suspect the compliance method used is to put the limits in
the handbook and put a placard in the aircraft. That's how
it's done in mine.

Here's the rule when VMO/MMO applies and Vne does not:

(d) ... 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.

My Vne red line is the speed at sea level, and it begins to
drop above 10,000' per the placard and flight manual.

I have
never seen anything in any of the flight manuals that I have (four)
referring to Vne going down with altitude. I am not disputing that it
does
but I am mystified as to why it isn't better explained in flight manuals.

If it's not placarded and doesn't appear in the flight
manual, you can assume the red line is correct up to maximum
operating altitude. Of course, you can fly airplanes above
service ceiling with some help from nature (wave lift comes
to mind), just as you can fly a glider, so you still want to
be aware of the common altitude dependency of Vne. You
can't really assume anything about Vne except when flying
within the limits.



"It is possible to fly without motors, but not without knowledge and
skill."
Wilbur Wright