Clearance to cruise at a given Mach number is also used by ATC to separate aircraft longitudinally on flights over non-radar covered areas, e.g. North Atlantic or South Atlantic.
Airliner performance tables in the POH or AOM like range etc are mostly based on Mach number.
I guess this is also related to the trip cost index constraint that is coming from their OPS department.
Ibra wrote:
otherwise why CAT can still use Mach numbers?
Probably because they’re often Mach number limited.
when ATC says fly 240kts (never ask me that yet), I guess they are referring to IAS?
Correct. TAS for planning, IAS for sequencing.
I thought it is N for nautical miles per hour :)
faa.gov
ENTER the True Air Speed for the first or the whole cruising portion of the flight, in terms of:
Kilometers per hour, expressed as K followed by 4 figures (for example, K0830), or
Knots, expressed as N followed by 4 figures (for example, N0485), or
True Mach number, when so prescribed by the appropriate ATS authority, to the nearest hundredth of unit Mach, expressed as M followed by 3 figures (for example, M082).
airways wrote:
It is definitely TAS
Thanks I always wrongly thought it was IAS 
(otherwise why CAT can still use Mach numbers? but probably the assumption is CAT & GA don’t mix ), a last one when ATC says fly 240kts (never ask me that yet), I guess they are referring to IAS?
It is not KTAS that goes in FPL it is NIAS
It is definitely TAS
tmo wrote:
Thread drift – why is it “KTAS” and in a flight plan we denote knots as N and kilometers as K? :-)
Probably because the abbreviations have different origins. The use of “N” for knots in flight plans is of course because the “k” in “knots” is silent so it is pronounced as “nots”.
RobertL18C wrote:
15/16 USGPH, an added benefit might be the ability to use skis and floats
That GPH is twice of a Mooney on similar KTAS (but can’t have it on floats/gass)
It is not KTAS that goes in FPL it is NIAS
15/16 USGPH, an added benefit might be the ability to use skis and floats. Never thought of the KTAS convention but it precedes Eurocontrol flight planning codes. :)
