I cut a lot of standing-dead... always tricky. Most of it is elm, a few oak... and if it's leaning, it's normally not leaning in the direction I want it to fall. Because of too many mishaps and close calls I've gone to rigging every one on a dead-head pulley, even if I have to string over 100 foot of cable to do so. The cable doesn't need to be placed real high on the tree, 10-12 feet will usually suffice. I put goodly amount of tension on the cable (come-a-long, winch, vehicle, etc.) before I start cutting, and then add even more after the face cut; the idea is to get it moving early in the direction I want it to fall... and keep it moving in that direction. Sometimes, if I think it's needed, I'll add a recovery strap to the end of the cable for the "bungee cord" effect. I want a sharp chain to make a fast back cut... the faster the better. If it's a real tricky situation I'll get some help, hook the cable to my truck (if I can), so the "help" can keep the line "pulling" on the tree all the way to the ground... near always the tree will fall right on top of the dead-head.
Right or wrong, I'm not much for using PPE, but I do put on the hardhat when I'm working under a standing-dead... they have a tendency to drop widow-makers when they start moving.