This site is being deprecated.
Please see the official X‑Plane Support page for help.
On Download page: http://www.x-plane.com/desktop/try-it/ they have:
DOWNLOAD FOR LINUX (64-BIT)
Other Platforms: Windows, macOS, & 32-bit Linux installers.
except it does not work. They should say "Only for Ubuntu people, we don't care about anybody else!" - really? IPv6 Required? PulseAudio Required? GTFO! XP10 Foreva!
This site is no longer being actively maintained.