It really is flaky if not properly installed!
It only runs on Internet Explorer and in newer versions only runs properly in compatibility mode.
To download a section its best just to print to pdf and save that (if you can get the print feature setup).
I run it on my home PC in Internet Explorer 10 but still haven't managed to get the print function working. I also get two pop up errors I have close each time but apart from that it all works. (Run IE10 in Compatibility mode).
Another tip is to go Uninstall all the Airbus stuff you can find in Add/Remove programs in Windows then when you start IE and run Airnav, allow it to install all the software it wants.
For your info my machine has the following plugins running (all installed by Airn@v)
HTML Printing 2.1.001
ISOView 7.0.607
ADOC Navigator Active X 1.11.0
Install Active X 2.0.0
Cortona Active X 5.1.0167
Hope this helps a bit, for what it's worth on the works machines we use a much older version of Internet Explorer and it all works wonderfully!