When I'm controlling on here I will undoubtedly refer to all 3 of these terms at different times and I have been asked in the past why they are different so hopefully this will provide some sort of explanation.
A flight level is based on a Standard Altimeter Setting(SAS) this is 1013Hpa or 29.92 Ins. All aircraft flying above certain altitudes (different all over the world but at the minute its 3000ft in the UK) should have this set to aid de-confliciton between aircraft.
A height is based on a pressure that has been corrected for the airfield elevation of where you are making approach (QFE). so when you sit on the ground at the airfield and have this pressure set your altimeter should read zero (or pretty damn close). This is what is used for making an approach to most uk military airfield.
An Altitude is based on a pressure that has not been corrected for airfield elevation (QNH). Most civil airports and aircraft use a QNH. When you land with a QNH set your altimeter should read the airfield elevation above mean sea level.
in the UK we have regional pressure settings(RPS) which are valid for 1 hour and are the lowest forecast QNH for that whole area. any aircraft flying on this pressure is also operation on an altitude. Similar systems exist in different countries all over the world.
The uk RPS map is below
Dave, do you know how the Typhoon deals with barometric altitude? Nowhere can I find any function to adjust the barometric altimeter's pressure setting, and thinking about it, it's probably not very difficult to do it automatically these days, but I don't know for certain.
I'll see if I can find out but its definitely not automatic. Each aircraft operating together has to set a common pressure setting. Regardless of whether this pressure is actually accurate in that specific bit of space.
Without a common pressure on each aircraft it makes safe operation in a training environment seriously difficult