Converting Mode C flight levels to altitudes
Hi
I know transponder encoders send out pressure altitude, and I know ATC can convert this value into an altitude to display on the screen.
I remember it is to do with the difference in QNH from 1013mb and then times it by 28ft and add that to the flight level reported???
What formula is used and what are the variables based on? Is it based on the pressure at the aircraft position or the ATC location? And does the altitude of the aircraft change the 28mb/ft bit of the formula? (I think this is related to temp and pressure???)
cheers
smithgd