Difference between QFF and QNH
Hi,
I'm in the US where these 'Q' codes are not common, and I want to better understand them.
I understand (I think):
QFE : Absolute pressure locally (usually at airport threshold).
ALT set with this pressure displays 0 on the field
(at the reference point, in ISA temp?)
QNH : Local barometric pressure at MSL (reported in METAR)
ALT set to this pressure displays Indicated Altitude
(true altitude if ISA conditions)
The references I have been looking at (WIKI & my old books) say that QFF is QFE reduced to MSL using station temperature used in weather reports (not METAR?), so that ISOBAR lines make sense given reporting stations different altitudes (and hence pressures). If this is so, then what is the difference between QFF and QNH?
Thanks for your expertise.