Catiamonkey has it right - FADEC (and any systems other that go outside the fuselage) are heavily shielded for things like lightning and HIRF. Electronics that are contained inside the pressure vessel are also shielded, but the threat is lower due to the shielding provided by the fuselage. If you're wondering, the 787 systems were designed for higher threats because the carbon fiber fuselage doesn't provide as much shielding as aluminum. Solar storms are pretty minor compared to the threats that we design for.
Several years ago Boeing was working on a specially modified 767-400ER, I think it was called an 'E-10'. Basically they were going to put a big, zillion watt ground search radar under the fuselage (they needed the extra length of the 767-400 to make it fit forward of the landing gear). Dual 150 KVA generators on both engines to power it.
Anyway, this radar was going to be direct line of sight to one engine's FADEC. I got a call from someone on the military side, wanted to know how much HIRF the FADEC could handle. I responded we tested to 200 volts/meter average field - what's your requirement? 'Can't tell you that, it's classified - what can you handle'. Again I responded 'we tested to 200 v/m, we didn't test to failure - how much more do you need?' 'That's classified'....
I was somewhat relieved when that program got cancelled..
