However, during the past four trips I've experienced a problem with the main mapping window freezing and completely blanking out - requiring me to reboot in-flight with all the distractions that involves. Only the map window develops a fault; the Enroute Features window and the ETA/Altitude data etc is not blanked out. Indeed when viewed later the flight log shows the GPS tracking continued in the background.

If no one else has experienced this issue then I suppose it might indicate a fault with the PDA, even though it is dedicated to SD and hasn't had any other software added since SD was originally installed. Any suggestions would be welcomed.

Posting a photograph of what the screen looks like when this happens might be helpful. Perhaps you can convince it to repeat during a local car journey?