QFF=QNH at MSL, question

[ft]

Or skip the math and look at what the altimeter settings really are.

For QNH you set the altimeter to give you the correct altitude above sea level when at the reference point (threshold). For QFE you set the altimeter to read zero when at the reference point (threshold).

If the threshold is at sea level, the altimeter should read zero in both cases. Ergo the altimeter setting must be the same. If it wasn’t, the readout would be different and either the altitude QNH or the altitude QFE would be off.

Edit: Note to self: Get off high horses and soapboxes and learn to read! QFF, not QFE.

The point is still valid though, no math required. If you reduce the pressure through an enormous altitude of zero meters, it doesn’t matter a whole lot whether you use ISA or the current temperatures.

Cheers,
Fred