1.) Aircraft do not have "unprotected" circuitry or every single lightning strike would fry our equipment. So it may not damage all equipment.
2.) Energy density is required to induce an electric field. The further away the lesser the problem. If you are close enough to have the circuitry fried your probably close enough not to have to bother for a landing anymore.
Try this:
http://www.qsl.net/n9zia/emp.html
more coming up when I can find it again.