"The airlines have apparently been sending out "scout planes" to explore which routes are usable, and for the most part have reported "no problems" for the routes they've tested."

Not exactly: http://www.bbc.co.uk/blogs/thereporters/robertpeston/

This poses an interesting problem; this is a natural catastrophe, and will capitalism be able to rise to the task of dealing with it effectively? The omens are not good as stranded passengers are being give the usual airline treatment of being ignored or infrequent impersonal communications, and the focus is moving to the economic rather than human cost. There seems to be some pressure from the airlines on NATS to allow some flights, and given the contempt the government and the media hold science in these days it remains to be seen whether caution or cost prevail.

For those of us living under busy flightpaths, it's been a once-in-a-lifetime chance to see clear blue skies sans vapour trails or roaring jets. That said, let's hope this clears soon and those people can get home.