OK… Back to GNS530 …
ETA Calculation
Interesting property of Ground Speed, that seems to affect GNS530 (MSFS , and maybe even RL GNS530)
In MSFS, GS is always Positive value, even if the wind is so strong, and you are actually moving backwards wrt ground, being blown backwards, away from your destination.
So when the GNS530 calculates ETA, if the plane is in effect moving backwards, the ETA should be NEVER (infinite) but as the GS goes through that zero point, the faster you are moving backwards (away from the destination) the ETA starts to reduce again.
For Practical purpose, this is probably not an issue – nobody flies a C712 in 100 knot + winds (only in MSFS) - but it was not till today that I appreciated the effect of GS always positive.
Its Actually even more interesting.
If you are heading AWAY from your Destination, the ETA also DECREASES, the faster your GS.
So, based on that, I think the current calculation using absolute GS as a “absolute” Scalar is Incorrect.
The ETA should be Calculated on the COMPONENT of your GS towards the Destination.
This would proved a solution to all the above, and make a lot more sense ???
So even in moderate winds, the ETA will be correct …
Got to wonder what the RL GSN530 does in this situation !!!
Also see : https://groups.google.com/g/apps4av-forum/c/MGqtJqv6W8w?pli=1
Gets even more complicated !!!
Looks like at the moment, ETA is only valid, if your Course is direct to Destination, and you are actually moving Towards the Destination.
Even then if flying on a course Towards you destination, if you are effectively moving backwards, you will get an ETA that will make you think you are going to get there in some specific time, and you NEVER will 
If course, having that nice new Wind Speed indicator in the GNS530 Mod, gives you a HINT when it displays a 110 knot headwind !!!





