Can cosmic rays shoot down aeroplanes?

At cruising altitude, planes get a heavier bombardment from cosmic rays than we do at ground level. So you need to be very sure that any critical electronics controlling the plane can cope.
The same applies to a lesser degree even at ground level, especially as electronic systems get smaller and faster.

Electronic devices rely on semiconductors. In metals, electrons are free to move around between atoms. In insulators they are tightly bound to the atoms and can't move. But in semiconductors they are almost free. All they need is a little nudge and they can carry an electrical current, and this is why we can use them to build complex devices by arranging exactly how and when any current will flow.
Unfortunately they can get a nudge from a passing cosmic ray too. This can turn a one to a zero in a computer's memory. Not too bad if it just means your mp3 player skips a beat, but terrible if the autopilot goes haywire.

A very good way to test electronics, and make sure this won't happen, is to put your prototype electronics in a beam of neutrons, which you can do at the ISIS spallation source in Oxfordshire. The neutrons fake the most dangerous cosmic rays.

ISIS suffered some severe cuts in that spending review, and was going to have to run below capacity. So I was very glad to see that a couple of days ago David Willetts, the Universities and Science Minister, announced a new £11 million investment in a project called "Chipir" on ISIS which will test the safety of electronic systems found in aircraft and cars.