I've only flown four times, and they were all on one trip when I was in my late 20s. I was already incredibly anxious about it beforehand and was seriously worried about having a panic attack once on board. Thankfully that didn't happen, but all of the flights were a bit turbulent and I got off the final leg of the trip vowing to never fly again. So I totally identify with your son, and I can reiterate what a few others have already said below - it's mostly about not feeling in control. At least in my case, safety statistics have absolutely ZERO impact on my fear. I recognize that my fear isn't all that rational, but at the same time, it's not something I can just ignore.

I feel for both you and for your son, as I do for my wife. She grew up in a military family and was used to living/traveling all over the world. We obviously don't do that now. However, she knew about my fear long before she married me, so she knew I would likely not be traveling all over with her. In your case, you are just kind of stuck being at odds with your son's fear. I'm not sure there is an easy solution, but I would caution against FORCING him to go along if there is a reasonable alternative way for him to stay behind with relatives. A trans-Atlantic flight would not be a pleasant time to have a panic attack.

Good luck.