Hillary was a nervous flyer. I'll try to put it into her words as much as I can. As in, not a direct quote, but she said something within a few words of this more than once.
"Well, in a car, if something goes wrong, I can just open the door and climb out. In a boat, I can swim or I'll have a life jacket. But in a plane? I know I can't fly."
Take off would be stressful. Landing would be worse. Any turbulence during the flight? Hillary would be white knuckling.
We would hold hands for long periods of any flight. She'd squeeze harder as she got more nervous but even with a low level of concern, her hand would be clammy with sweat.
She was conscious of this and didn't want to make the kids into nervous fliers because she was. When she and I would be split into two different rows with one kid each, she'd go out of her way to force a normal, cheerful demeanour even if the flight was bumpy.
For most of the flights in the last two years, the seating arrangement would be me with the two kids and Hillary across the aisle. My reasoning was generally that I wasn't going to sleep on the flight anyway. Hillary might. That meant that when we got there, she could be the one who was slightly more rested.
I don't think Hillary minded this arrangement all that much. Though she did comment more than once that she looked forward to when the kids were old enough and fine on flights so we could sit together again.