Please consider adding a new Simvar "Nav Airport:index"
Currently, when an Active Loc/ILS/LDA is selected by a NAV radio, there is no SDK way to get the ICAO code for the Airport for that Loc/ILS/LDA .
ie To get the airport KDCA in the left Blue Window, in the Garmin GNS530 GPS, and similar units.
"Nav Name:index" gets the LOC/ILS/LDA's runway (LDA 19)
"Nav Ident:index" gets the LOC/ILS/LDA's ICAO code (IVWH)
But there is no Simvar to get the associated Airport "KDCA"
ie no "Nav Airport:index"
Note: Actually "Nav Name:index" gets the LOC/ILS/LDA's runway (LDA19) - No space between LDA and 19, but thats easy enough to re-format in the GPS code. to 1:1 match the Real World GPS formatting.