[klem]

You'll understand if I don't take up matlab, C# is enough of a challenge!

Those formulas are generally what I am using.

btw I assume our TLR_Cpm is for altitude in feet not metres (TLR_Cpf?).

The problem we have for calculating Density Altitude is that there is no OAT indicator. Then there is the question of whether Z_AmbientTemp relates to the cockpit altitude.

I did calculate a lapse rate from Z_Temp and Z_AltMSL and assuming 288.15 at SL but that gave daft results.

So I have assumed Z_AmbientTemp as OAT. I crashed at SL and it returned 290.1K or ~17C. At 15000ft it gave 260.2, a lapse rate of 0.0019933 for the CoD environment so I guess its OK for our purposes.