ATC: Knots vs. Mach?

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

On Wed, 07 Jul 2004 19:29:06 -0700, AES/newspost
wrote:

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".

For the jet crew out there.... What's the transition point between
mach and airspeed callouts? FL180?

For us it is variable. Mostly with temperature. For instance, we normally
climb at 270 knots until M 0.75, and continue referencing Mach.

Also, if you select a target speed with the FMS it is IAS until 24,350 and
then the numbers automatically turn to Mach by the computer.

I've never really though too much about it. If ATC wants your speed you give
them IAS. If they want your Mach, they ask for Mach. If a chart is
referenced IAS, we use IAS. Some charts are referenced Mach, then of course,
Mach is used.

Karl

"Nathan Young" wrote in message
...
On Wed, 07 Jul 2004 19:29:06 -0700, AES/newspost
wrote:

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".

For the jet crew out there.... What's the transition point between
mach and airspeed callouts? FL180?

"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.

"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.