encoding altimiters send the info to the transponder as a flight level regardless of the setting on the subscale. the controllers then work out the appropriate altitude on the ground, whether this is done by the computer or the controller i dont know( any ATCO's wish to comment?)
imagine the chaos if it transmitted the altitude indicated, with people operating on QNE,QNH and QFE in the same area!
about the orange box, thats a good question. i would imagine that it gets its info (in at least duplex) from the altimiters as a FL, with any discrepances being worked out by some rather clever people in a lab after the event! remember that the box itself is just a data recorder so therefore doesnt need calibrating,just checked to ensure its operating on all channels/inputs.
Last edited by andyb79; 7th Aug 2004 at 00:48.