Tim,
Superb job on the software - really like it.
Rather than reinvent the wheel... global airfield and navaid data is available under GPL from the X-Plane (flight simulator) data site
X-Plane airport & navigation data - Home page.
Obviously... it should be checked for accuracy before using for real flights, but it's a massive repository of data, mostly gleaned from official AIP sources.
While I'm here...
Happy to report that SkyAngel Plan works on Linux. Need to use VirtualBox rather than WINE, so Windows is still required.