# Understanding QFE, QFF, and QNH MET

A number of qualitative questions from the exam.

• If you land with QFEQFE —Static pressure measured at an aerodrome set then the vertical distance indicated will be above the airfield. This is zero on landing.
• If you land with QNHQNH —Static pressure at MSL calculated from QFE using ISA temperature lapse rates set, then the vertical distance indicated will be above mean sea level. This is elevation on landing (and it does not matter that you do not have ISAISA —International Standard Atmosphere conditions.)

The difference between QFEQFE —Static pressure measured at an aerodrome and QNHQNH —Static pressure at MSL calculated from QFE using ISA temperature lapse rates is a function of the distance to mean sea level and the ISAISA —International Standard Atmosphere lapse rate. As the latter is a standard number, to get between QFEQFE —Static pressure measured at an aerodrome and QNHQNH —Static pressure at MSL calculated from QFE using ISA temperature lapse rates requires only knowledge of the elevation.

The difference between QFEQFE —Static pressure measured at an aerodrome and QFFQFF —Static pressure at MSL calculated from QFE using actual temperature lapse rates is a function of the distance to mean sea level and the actual lapse rate. As the latter is not known, to get between QFEQFE —Static pressure measured at an aerodrome and QFFQFF —Static pressure at MSL calculated from QFE using actual temperature lapse rates requires knowledge of the elevation and the lapse rate. Irrespective of whether you are discussing QFEQFE —Static pressure measured at an aerodrome v QNHQNH —Static pressure at MSL calculated from QFE using ISA temperature lapse rates or QFEQFE —Static pressure measured at an aerodrome v QFFQFF —Static pressure at MSL calculated from QFE using actual temperature lapse rates, the higher up you are, the less the pressure.

As the difference between QFEQFE —Static pressure measured at an aerodrome and QNHQNH —Static pressure at MSL calculated from QFE using ISA temperature lapse rates is a function of the distance to mean sea level, if this distance is zero (elevation is zero or the airfield is at mean sea level: these mean the same thing) then there is no difference between QNHQNH —Static pressure at MSL calculated from QFE using ISA temperature lapse rates, QFEQFE —Static pressure measured at an aerodrome and QFFQFF —Static pressure at MSL calculated from QFE using actual temperature lapse rates.