True Altitude?

[FrankB]

Thanks Soldier, you are da man!.

The math is quite simple once you have the missing link, which, for me was your equation [1].

Reviewing my research I saw the equation before, but

1. In a different form: TAS = EAS*SQRT(AD@MSL / AD_ALT) and then the definition of EAS introduced dynamic pressure or Mach number and I never got results at least close to yours.
2. With a remark it is valid only for low-speed flight (~0.3 Mach)