Good evening HN39,
The sentence of mine you quote has effectively been rubbished by me, by virtue of my apology above. [I was mistakenly under the impression that you were arguing that FPV was based on TAS, which would have made the FPA relative to the airmass, not the earth.] Am tempted to amend my post, but that seems dishonest, and I doubt it will be read in isolation.
You raise another interesting point about the alleged dependence of the FPA/FPV ("bird") on VS data from the AD. The pressure lapse rate in the atmosphere does indeed vary with temperature deviation from ISA. I suppose the air-data system may correct for that, but that's me guessing again...
The cockpit altimeters do not correct for temperature deviation, presumably to keep all aircraft "singing from the same hymn sheet" for ATC separation purposes, and also because the AD system cannot know the temperature deviation of the entire atmosphere below the aircraft.
Last edited by Chris Scott; 22nd Mar 2010 at 22:53.
Reason: Syntax improvement.