Mach to Airspeed Transition

[Terry Hunter]

ATC Guru's:
When a controller says "maintain 300 knots during the transition", what is the transition point at which the controller is referring to? I presume at a certain altitude and above, that ATC wants speed in Mach?

Thanks.
TH

 

[Choppy]

Basically hold a certian mach number until you get to 300 kts indicated and then hold 300 kts. Altitude will maybe be different each time.

 

[J.Otto]

usually the mid 20's

 

[Terry Hunter]

Thanks

 

[macdu]

Usually, between FL27/28 depending on the temperature.

 

[Mercy98]

Generally, aircraft that cruise at FL300 and above, and normally cruise at .75M and above have an indicated speed in the low to mid 200kt range. As they descend, they fly a constant Mach number, but the indicated speed increases. Once that Mach number matches a particular indicated speed, then that indicated speed is maintained.

The Mach number cannot be maintained at some point because it eventually will increase above the barber pole. There's no flying above that of course.

Typical indicated speeds that are maintained range from 280-340kt. If ATC wants a particular speed, so be it. Hope that helps.

 

[pilotyip]

FL240, the transition altitude between the highand low sectors. Above 240 Mach, below IAS

 

[BillJBrake]

macdu is correct, between FL270 and FL280. Technically a mach number can be assigned lower than that, and an indicated airspeed higher than that, but it's usually only if they're climbing/descending into the preferred regime.

PilotYip, not sure where you get FL240 from but that's a bit low to be used as a "standard". There isn't an arbitrary transition altitude between high and low sectors.

 

[Mike man]

Generally, aircraft that cruise at FL300 and above, and normally cruise at .75M and above have an indicated speed in the low to mid 200kt range. As they descend, they fly a constant Mach number, but the indicated speed increases. Once that Mach number matches a particular indicated speed, then that indicated speed is maintained.

The Mach number cannot be maintained at some point because it eventually will increase above the barber pole. There's no flying above that of course.

Typical indicated speeds that are maintained range from 280-340kt. If ATC wants a particular speed, so be it. Hope that helps.

What a terrific explanation...good job

 

[pilotyip]

Taught in Ground School

macdu is correct, between FL270 and FL280. Technically a mach number can be assigned lower than that, and an indicated airspeed higher than that, but it's usually only if they're climbing/descending into the preferred regime.

PilotYip, not sure where you get FL240 from but that's a bit low to be used as a "standard". There isn't an arbitrary transition altitude between high and low sectors.

http://www.faa.gov/library/manuals/aviation/instrument_procedures_handbook/media/CH-03.pdf

ATC issues speed adjustments if you are being radar controlled to achieve or maintain required or desired spacing. They express speed adjustments in terms of except that at or above FL 240 speeds may be expressed in terms of Mach numbers in 0.01 increments. The use of Mach numbers by ATC is restricted to turbojets. If complying with speed adjustments, pilots are expected to maintain that speed within plus or minus 10 knots or 0.02 Mach.