There are manual pins that have to be moved by a lever, and sometimes a lever and button. To get the slide pack to deploy when airborne, the door would have to be "disarmed" intentionally and the slide lever pulled. It's either that or the slide pack wasn't installed correctly to start with by the ground crew. Boeing wouldn't be to blame for this or it would be happening a lot more often.

Just what I thought.

Total incompetence In maintenance department!

UA’s reputation just keeps sinking lower when it was already near the bottom.