with "unstoppable" electronics
Was listening to an interesting programme on Radio Four last night about GPS jamming. (apparently the increase in employees movements being tracked by GPS has led to a big increase in cheap, handheld GPS jammers.)
Anyway, according to the programme, the biggest jammers of GPS are large solar flares. Now a single aircraft losing the signal for 20-30 seconds halfway across the Atlantic is no big deal but every aircraft simultaneously losing their GPS in the skys over New York or Chicago is more of a bigger deal.