reasons behind speed control

[mxwbuaa]

hye, anybody knows the the base on which the rules about speed control are made?
the rules which is specified in icao doc 4444 are: At levels at or above 7 600 m (FL 250), speed adjustments should be expressed in multiples of 0.01 Mach; at levels below 7 600 m (FL 250), speed adjustments should be expressed in multiples of 20 km/h (10 kt) based on indicated airspeed (IAS).
Speed reductions to less than 460 km/h (250 kt) IAS for turbojet aircraft during initial descent from cruising level should be applied only with the concurrence of the flight crew.

[zkjaws]

Pretty straight forward really:
Above FL250 speed is usually referenced to Mach Number and 0.01 would be the smallest increment that a pilot would be expected to fly to.
Below FL250 speed is referenced to Indicated Airspeed and 10kts would be the smallest increment that a pilot would be expected to fly to.

The minimum speed of 250kts for the initial descent (at altitude) would be not far off the mimimum clean speed for a jet aircraft - dependent on weight etc.
Any slower and the aircraft would be approaching the stall speed or would require the use of flap.

[On the beach]

B747's, if number one, should be descended at mach .86 into 340kts. Everything else just tags along behind. Mind you, if you're a B747 and aren't number one, then you've just discovered the reasons behind speed control. :E

Bring back Tridents - 320 to 15. :ok:

[topdrop]

Westwind 350 til 5

[bekolblockage]

Topdrop
:ok: Recall 360 to 6 into Melbourne on the night shifts, so same same. Call us on Approach at 35 miles just left F350 on the drop. Straight in 16, 10,000 at Bolinda. Cool.
Loved watching trainess try to make you number 2. :eek: [Edit to add: What our Flows used to refer to as a "gorilla with a machine gun" i.e. Don't let anyone get in his way - give him what he wants! :}]

mxwbuaa
Not exactly sure what you are driving at but you need to understand the concept of aircraft transitioning from IAS to Mach No. on the climb and vice versa, on descent.

For most jets that happens around 26-28,000 ft so although F250 is a touch on the low side it is chosen as a cutoff where Mach number or IAS instructions should normally be issued.
In fact, decent en-route controllers (like On the beach :ok:) will normally provide a reduced Mach No. into an IAS if a speed reduction is required from top of descent. e.g. M 0.80 into 270 KIAS.
If you just say 270 KIAS on descent, that can actually be a speed increase at upper levels.
It's instructive to look at a table of IAS, Mach No., TAS vs Altitude to learn what is going on up there.

[ron83]

Had once an MD 83,was doing 320 on base,than 250 till 10:}

[TC_Ukraine]

hi, everyone.
Question: Why the aircraft's speed is expressed in Mach numbers above exactly FL 250? I mean not 220,230, 260 etc. How was it calculated?
And yes, I tried to google it. Coundn't find answer

[Vercingetorix]

Mach Number - NASA
Mach Number (http://www.grc.nasa.gov/WWW/k-12/airplane/mach.html)

:ok:

To infinity and back and, hopefully, in time for tea.