Hi Steve, The Airnav Acars Decoder locks up when used with XP (it is the program which locks, not XP, as everything else still works at least on my machine). You can try Wacars which does work, but I have found that using my old Pentium II machine using Windows 98 SE works much better for Acars, I have Sky-Spy and the Airnav decoder on it and all is well. Best regards - Mike Simpson, Penrith, NSW