QFE vs QNH options
Beware mixing the two... The fcu may have a QFE option ( they sometimes default to this on power up in the A330 for example)
This is NOT the same as the QFE pin programming on the FMS..
Which can be identified by the approach page having MDH instead of MDA ...
There are issues with the qfe programme.. not the least are issues doing fully managed approaches, or lnav vnav for Boeing dudes...
Some like the egpws isssues mentioned earlier, some like the fact that you can only type mdh values in up to 5000 feet , so how do you remedy that one into say Nairobi, Kunming or Sanaa for example?
There is a section in the FCOM about the issues...suggest you resd it closely.
And the autopilot has different disconnect points ... Which can be briefed but might be unexpected if you are not prepared.
There is also a bulletin about copying the secondary over to the primary and getting an erroneous value in the MDA/ MDH field by the elevation etc...
Overall, be very careful how you use any of these would be my advice.
In China Southern for example I asked about what they do when they go to a high alt airport ( they have QFE pinned FMGS) I was told they just use the MDA...but my answer about why not type in the MDH for lower airfields , and when would you change over was a bit vague...
In summary... The charts that convert QFE/QNH metres etc as designed for each airfield seem complicated but they would appear to be the safest I have seen...
The key there is not to have the metres button selected below transition as that can screw you up ( it just messes with your head a bit) in Russia for example... Ask emirates ..they had a few incidents with that a while ago. Lucky domodedevo is pretty flat...
MW