questions on braking conditions and radar
 

how do controllers suppose to know the runway's braking condition when pilot ask this when on final approach?

and some controllers use mach nos on high level decents, and some use ias??

And in the parts of the world where we experience winter conditions etc often, ALL airports with ATC or AFIS/FIS have one........ :

We use it all the time in the winter, after the runway has been swept, and when we (ATC) think it is warranted. (I a pilot reports report less BA then we have reported etc)

The car (A Saab 9-5 Estate here at Bardufoss/ENDU) often do testruns inbetween landings, when the aircraft lands, the car starts the run following the aircraft down the runway. A return run has to be made, in all it takes about 5 minutes. You need about 15-20 miles spacing on final to get a testrun in between.
(2443 meter rwy)

All good radar controllers (and some bad ones too) know that a/c fly Mach above certain levels and then switch to IAS once lower. If an a/c descending is given an IAS to fly while still in Mach mode, words to the effect of "when able" are added. It just means that during Mach there is no problem, but one may occur on IAS. Other controllers need to control the mach too, so normally regulate that first then give an IAS to convert to. Basically it all amounts to the particular controller and certain situations.

For Breaking Action, In Marseille airport (where it snows once every other year ;-) ), we have a special device that can be attached to any car...it takes longer than a check with a special vehicle...but it works well!