View Full Version : ADS-C and Indicated versus True Mach

12th Feb 2019, 19:44
I haven't used ADS-C yet on our EASy II equipped falcon, however I have looked up the difference between true mach and indicated mach in the relevant performance section. For a True Mach of .80, the pitot static calibration curve show this to be an Indicated Mach of .813

So I'm expecting to fly at .813 indicated, when assigned a true Mach of .80

And I'm expecting .813 to be sent via ADS-C, would that be correct?

And if so, how much of a mach variance does it take before oceanic control gets concerned? In this case it would be Mach .013

However, the mach correction gets even larger as the mach increases above .80 true



12th Feb 2019, 22:10
I never used any conversions when using ADS-C (744, anywhere up to .87 IMN). Just dial your assigned Mach into the MCP.

13th Feb 2019, 16:54
Intruder, perhaps the 744 has almost no difference between true and indicated mach?

I'm wondering if ATC would question our .84 indicated mach ADS-C report when .82 (true) was our clearance.

Maybe it was just the older days when that was any concern.

13th Feb 2019, 23:02
Shouldn't ATC be aware that not the true but indicated mach number is being reported via ADS-C?
(Maybe there even is a correction implemented in the ADS-C module for your airplane, you could of course just ask ATC what mach speed is displayed for them)

No matter what is reported to ATC you should follow your clearance, shouldn't you?

Anyway maybe one of those two links can help you:
Mach Number Technique (http://code7700.com/mach_number_technique.htm)

18th Feb 2019, 18:40
I submitted the question to the ATC forum. Wait and see.