Originally Posted by AustinBear

I was on a flight a few days ago and there was a very tall (and somewhat large) passenger who could not fit in the seat with the armrest down. He needed it up to articulate his right leg enough to fit under the seat in front of him

I don't know what the rule is, but the FA helped him pull it up. He was in an exit row in which it was fixed. Apparently there is a button at the rear of the armrest that releases it to be raised.

Seems if you were belted properly, it would not be a safety issue - except perhaps when the carts come down the aisle!