Dave has brought this to us :
A lot of civil aircraft are kept clear by inserting a tube into the lower
edge whose other end is connected to a silica gel container, but that would
be difficult to do with a DG window.

Not to mention the cost of hiring an aircraft to take the panel up :-)

--
Regards,
Harry (M1BYT) (L)
http://www.ukradioamateur.co.uk