Density Altitude Equation on HP 35s

[ptros]

The calculation on Wikipedia is okay but it assumes dry air therefore your Density Altitude will indicate lower than actual. We are calculating humidity (water vapor) indirectly by using the dew point. Humidity displaces air which decreases lift which results in a higher density altitude. That said formulas which assume dry air are not specifically dangerous to use given temperature is the primary driver. If using a dry air Density Altitude formula results in an aircraft's performance to be at threshold then one might assume calculating humidity will be more definitive in finding that threshold, and it will. But on those hot humid days its better to leave the plane in the hanger and do something else until temps cool down.