Originally Posted by
SThor
Hey.
I believe the ADS-C reports show the indicated mach number as cleared rather than the true mach number you might actually be flying. Don’t quote me on that though but I would believe that it’s similar from an ATC perspective as IAS vs. TAS, you fly a certain TAS to comply with a cleared IAS and that changes with altitude etc etc. You’re cleared M.083 and you are a true M.0812 to fly an indicated M.083 as input into the FMS then you are considered and shown as doing a M.083.
ADS-C reports show if there is a discrepancy between actual vs. cleared route for instance. If a different fix/route is inserted into the FMS than is cleared a message promts and advises the controller. Would probably be the same action if a report shows a different mach than cleared.
I've never flown with ADS-C, and haven't flown the Atlantic for quite a few years, however ATC always assigns a True Mach. We then converted that to an indicated mach, and flew this indicated mach on the mach meter. Eg for an assigned true mach of .75, we flew an indicated mach of .76 on the mach meter.
ADS-C I believe sends the mach indicated by the air data system, in this case it would be the .76 value. Hence the question I have for our new Falcon 2000, an assigned true mach of .82 would be .84 indicated mach for this aircraft. So ATC would continually receive .84 via ADS-C when .82 was assigned.
Does this make sense?