ATC: Knots vs. Mach?

"AES/newspost" wrote in message I appreciate that these are occurring in
quite different ranges of
operation and the units involved are very different in scale, but I'm
still curious about the potential confusion, or at least possibility for
same, in using two different sets of units for the same quantity

Controllers will preface the number with the appropiate scale. Additionally,
Mach will be a 2 digit number whereas Airspeed will be a 3 digit number.

Do different levels of ATC consistently use only one of these units and
not the other?

No

Do cockpit instruments read in both units, or are there
two separate "speedometers" (or a switch that has to be thrown to read
in one or the other)?

Both units are on the same instrument simultaneously.

What's the smallest _civilian_ aircraft that will
have a mach meter?

The 6 passenger CitationJet comes to mind.

Do prop or turboprop airliners have a mach indicator?

Most do not. Props are not efficient at airspeeds of Mach concerns.

D.

"Nathan Young" wrote in message For the jet crew out there.... What's
the transition point between
mach and airspeed callouts? FL180?

As we climb, the outside air temperature drops. As the temperature drops,
the speed of sound drops. We climb at indicated airspeed (not true airspeed)
until mach climb airspeed matches indicated airspeed, at which point we
transition over from indicated airspeed to mach airspeed. For the jet I fly,
the transition occurs around FL240 (24,000') depending on outside air
temperature.

D.

Some flight guidance and control systems automatically switch from IAS to
Mach at a given Flight Level. Example would be the MD-80 DFGC. If the
IAS/Mach switch is pushed below FL 270 it shows and controls current IAS.
If the same switch is pushed above FL 270 is shows and controls current
Mach.

--

B-58 Hustler History: http://members.cox.net/dschmidt1/
-

"Mark Hewitt" wrote in message
...

"Really Me" wrote in message
m...



At or above FL240, express speed (IAS) in Mach
Below FL 240, express speed in knots

Any reason?

Yes, but remember that Filght Simulator is not a good benchmark. Flight Sim
is "dumb", it doesn't know anything. It uses lookup tables, not aerodynamic
modelling, for aircraft performance.

"Charles Newman" wrote in
message ...

In Flight Simulator, I use knots below 14,000 and Mach above 14,000.
Below 14,000
true airspeed and indicated speed are pretty close, but above 14000, they
start to drift
apart quite rapidly.


"BTIZ" wrote in message
news:yC4Hc.15044$z81.6157@fed1read01...
IIRC.. from controlling traffic more than 25 years go..

Speed control for spacing, must use Mach numbers above FL290.. not
Indicated
airspeed in knots.

Below FL290, or was it FL250, use of IAS in knots is standard..

Ref: 7110.65 (which I do not have handy right now)

BT

"AES/newspost" wrote in message
...
Listening to audio channel 9 on United, at higher altitudes and during
cruise I hear ATC say things like "What's your mach?" and "Maintain
mach 77" and at lower altitudes and during approaches "slow to 180" or
"maintain 250 for spacing".

I appreciate that these are occurring in quite different ranges of
operation and the units involved are very different in scale, but I'm
still curious about the potential confusion, or at least possibility
for
same, in using two different sets of units for the same quantity
(especially when you recall incidents where confusion over units has
led
to loss of satellites, or airliners running out of gas).

Do different levels of ATC consistently use only one of these units
and
not the other? Do cockpit instruments read in both units, or are
there
two separate "speedometers" (or a switch that has to be thrown to read
in one or the other)? What's the smallest _civilian_ aircraft that
will
have a mach meter? Do prop or turboprop airliners have a mach
indicator?

in one or the other)? What's the smallest _civilian_ aircraft that
will
have a mach meter? Do prop or turboprop airliners have a mach
indicator?

Must get a new ASI for my "Hovey Delta Bird", maybe I can get one with both
scales?
;)
Peter