Hello,
Um... reading this kind of post one has to be careful. Here are my interpretation:
QNH = actual measured pressure at SL
QFE = actual measured pressure at aerodrome (so QFE = QNH if aerodrome is at SL)
QFF = estimated pressure at SL calculated with a QFE measured at an aerodrome above SL and measured temperature
Now, Ft:
The mess when calculating it stems from the fact that the weight of that layer of atmosphere depends on the temperature in said layer. You either assume ISA temperatures and get a QNH or you base your estimate of the weight of that layer on the current temperature and get QFF.
Should we say "You either assume ISA temperatures and get a QNH'..."? Isn't QNH = actual measured pressure so if it is an estimated QNH it should be called QNH'?
Now Xacto, where can I read more about the derivation and the application of the formula you posted? Was it from a book?