Steps to replicate: Install Redstone Arsenal and AS, power any piece of armor or the elytra (only crashes when powered), put on armor.

Some crashlogs thanks to Not Enough Crashes:
https://bytebin.lucko.me/cLh1ED4Y6h
https://bytebin.lucko.me/Q7Tdt8n0XP
https://bytebin.lucko.me/v6VBGKIZi4
I can't make much sense of them, but the fellas at the CoFH discord confirmed that it's AS causing the issue.

Just got word from the CoFH devs, apparently this issue will be fixed in the next update to Redstone Arsenal. I'll leave the issue up until then. (Just to make sure)