Quote:
Originally Posted by CaptainDoggles
Boy. I thought I'd seen some moronic arguments in my time, but this really takes the cake.
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I have to disagree Doggles...wildly O/T but a very interesting argument. A lot to be learned from these arguments IMO. And it is not about whether Biggin Hill is at +/- 1ft.
Interesting in that you can see the practical problems associated with having different aircraft flying around relying on pressure sensors (aneroid barometers) that are measuring pressure but displaying altitude or height values.
If everyone sets their altimeters for QNH (current SL pressure), the departure altitude displayed will be close to the surveyed airfield chart height but QNH will need to be continuously updated via radio with the passage of time and distance. Airfields and terrain will be collided with at their correct height, and aircraft in the same airspace will display similar altimeter values, but only if all aircraft are being continuously updated with appropriate QNH via radio.
If everyone sets their altimeters for QFE, height data is only appropriate for the departure airfield for a short period of time.
If everyone sets for QNE (standard pressure), all aircraft altimeters are reading the same flight level (within instrument error), a plus for managing traffic interactions. No updating is needed. However terrain and airfields may appear at different altitudes than physically surveyed data.
Crumpp, it sure seemed, even re-reading, that you were stating that physical airfield elevation was changing in some manner according to pressure and temperature (either physically or to some procedural convention). If you didn't mean that, what did you mean exactly?