Accurate Temperature Correction Formula
I am trying to develop an Excel formula for exact temperature correction for a friend, following the "accurate" formula from PANS-OPS Section III 4.3.4.1:
Correction = trianglehPaircraft - trianglehGaircraft = (-triangleTstd/L0) * Ln[(1 + L0 * trianglehPaircraft)/(T0 + L0*hPaerodrome)]
Where:
trianglehPaircraft = Aircraft height above aerodrome (pressure) ft
trianglehGaircraft = Aircraft height above aerodrome (geopotential) ft
triangleTstd = Temperature deviation from the ISA temperature K
L0 = Standard temperature lapse rate with pressure
altitude in the first layer (sea level to tropopause)
of the ISA.(See note (b) below) K/ft
T0 = Standard temperature at sea level K
hPaerodrome = Aerodrome height (pressure) ft
I have devised the following Excel Formula:
=(-"ISADEV"/-0,0019812)*LN((1+-0,0019812*"MDH")/(288,15+-0,0019812*"APAlt"))
where "ISADEV" is the temperature deviation from ISA (usually a negative number in cold weather)
"MDH" is the minimum descent height in ft
"APAlt" is the airport altitude in ft
-0,0019812 is the lapse rate in K/ft and 288,15 is ISA/sea level in K.
This results in meaningless results.
I am challenged by not really understanding why the basic formula should work and would be grateful for any hints on where I might have erred in applying it.