Mach Number question?

[Sheep Guts]

Gday All,
Im just enquiring why ATC in a RADAR environment, uses Mach Number for procedural seperation ie. I hear quite often which ever Centre Im on while flying (not a jet) they ask traffic whats their mark number and ask them how much faster they can cruise etc using this figure. I thought Groundspeed would be more logical. Or is it that they use it as a guide when looking at the traffics GS on the screen?

Hey just wondering?

Sheep

I just found the answer. Mach Number is used by Jet Pilots because of compressibilty problems and the fact that all performance data is based on this. Hence when asked by ATC if they can cruise at a higher MachNo. depends on their Altitude and close proximity to high speed buffet. Well atleast I think I found the answer. Thanks all concerned.
Sheep

[divingduck]

Hey Sheepguts,

We also use the Mach number for the mach number separation standards across non radar areas like oceans etc.

Many of the places that surround us here in the ME don't have radars so we have to set them up with either 10 minutes, no closing, or with the faster ahead by a certain speed vs time.

Very handy thing if we could only get Bombay to agree:{

[Spodman]

If aicraft have closing mach number we may offer a speed reduction to number 2 rather than changing level.

If they are at the same speed but the distance is close controllers may impose a speed restriction so they may be informed if #1 wants to reduce speed or #2 wants to go faster, thereby bending our separation standard.

We can't impose a restriction on an aircraft's groundspeed, as that depends on factors outside the pilot's control, so we "peg" the mach numbers and add a bit extra on "for mum".

Comments about mach number technique from the duck relevant also.