Roy Vegard Ovesen wrote: >On Sunday 21 January 2007 19:15, John Wojnaroski wrote: > > >>Likewise, not sure where you're going with this. ATC simply reports the >>current altimeter setting to the pilot. Above FL180 all altimeters are >>set to 29.92 or 1013. Encoding report aircraft altitude, otherwise ATC >>relies on what the pilot reports as aircraft altitude. >> >> > >I did a lot of research when I wrote the code for the encoder and transponder. >Unfortunately I didn't note where I found the information. I seem to remember >that the encoder encoded the pressure to pressure altitude, _not_ ASL >altitude. I'm searching the web right now to try and find info that can >confirm this. > > > >>But you might try >> >>Ref. Aviation Formulary, Ed Williams, www.best.com/~williams/avform.htm >> >>for data on a standard atmosphere >> >> > >Thanks for the link, I'll look into that. > > > > FYI for anyone interested in the topic and how things work....
All encoding systems, whether they are built into the altimeter or not, transmit your altitude corrected to 29.92 inches, or standard barometric pressure. ATC's ground equipment makes the altitude corrections directly onto the controller's screen. In short, what you dial up on your altimeter has no effect on what they see on their screens. There are no specific operating instructions for using an encoding altimeter other than setting it to the local barometric pressure and selecting Mode A/C on the transponder. The computer at the ground radar site as well as the altimeter electronics are referenced to 29.92" Hg. This means that the altimeter always supplies altitude codes based on 29.92" Hg regardless of the altimeter's barometric setting. The ground computer automatically computes the difference between the "29.92 altitude" received from the aircraft and the local barometric pressure. It presents the controller the proper "MSL altitude." Since the altimeter electronics are referenced to 29.92" Hg, changing the altimeter setting does not change the controller's altitude readout. No cheating allowed ;-) Regards JW ------------------------------------------------------------------------- Take Surveys. Earn Cash. Influence the Future of IT Join SourceForge.net's Techsay panel and you'll get the chance to share your opinions on IT & business topics through brief surveys - and earn cash http://www.techsay.com/default.php?page=join.php&p=sourceforge&CID=DEVDEV _______________________________________________ Flightgear-devel mailing list Flightgear-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/flightgear-devel
