the climbing rate gauge should have HUGE variations caused by atmosphere

[jf1981]

Originally Posted by zipper

Interesting. Here in the US we use pressure altitude (QNE) only for all aircraft above 18000 ft MSL. Below that the combination of not wanting aircraft flying into the ground (unintentionally) during airport operations with reduced visibility and having those aircraft (below 18000 ft), both terminal and en-route, synchronized vertically requires that they all set their altimeters to their local pressure settings (QNH). Any air traffic controller or Flight Service Station can provide local pressure information, and will give it (and winds, etc) spontaneously after querying intentions.

Yes, in France depending upon where you are, the transition altitude varies, if not indicated 3000 ft used, but currently eg 5000 ft may be used instead in controlled areas. Apparet from that, it's flat land so in mountainous areas I really don't know what rules are applied there, we have some cities in the alps. Have to have a look at it.