The easiest way to put APM Planner on Linux Ubuntu machine is to download the installer from here http://download.qt.io/official_releases/qt/ Qt5.4 or greater and then grab the code and build it in QtCreator or the command line.
It will work with 14.04LTS
The issue is building pre-built packages for 14.04 etc… This requires more effort and work and needs a ppa, or embedded qt binaries in the installer. If somebody wants to step up and build the needed ppa that would be great. In the meantime it’s the limited set of prebuilt packages.
We are maintaining compatibly at the code level with older distros, so you won’t need an OS version update.
Hope that helps 