The http://home.flightgear.org/download/main-program/ page points to version 2018.2.1 for MacOS, but the file does not exist anymore!
It should now point to version 2018.2.2 (https://sourceforge.net/projects/flightgear/files/release-2018.2/FlightGear-2018.2.2.dmg/download)
Thanks.