"Darkwing" theducksmail"AT"yahoo.com wrote in message
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"Wolfgang Schwanke" wrote in message
...
es330td wrote in


In theory you could use GPS altitudes when flying MSL/QNH setting,
because both systems measure absolute altitued, so you would expect
them to be the same. If GPS could be relied upon that is. Unfortunately
it cannot, GPS altitued measurements are unrealiable and can drift
wildly (as opposed to GPS 2D positioning which is quite accurate).
Traditional altimeters are much better.

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I'd like to jump right on the floor


If GPS altitude is unreliable how do you shot a GPS approach or is this
why WAAS was implemented?

Standard GPS approaches a flown with the altitudes from the altimeter. WAAS
approaches rely on GPS position correction from a local transmitter.


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*H. Allen Smith*
WACO - We are all here, because we are not all there.