Thank you. My old career Army dad taught me gun safety at a young age.
I don’t know why anyone would carry a pistol with a round chambered in an aircraft unless he was expecting big trouble. It’s not like it’s takes a long time to rack a slide. (I assume he wasn’t carrying a revolver.)
Even if you were going to parachute into combat, I don’t think you would exit the aircraft with a round chambered in your weapon.
A negligent discharge is caused by either ignorance or carelessness. The person can be considered ignorant, if they have not been trained. They are careless, if they disregard their training. There is no such thing as an accidental discharge.
There are absolutely ADs. They are far more rare than NDs since they require an unlikely mechanical failure of the weapon, but they do happen. I had a .50-cal AD during a patrol on one of my Strykers due to a mechanical failure. CO and BN armorers looked at it and concluded the same thing—mechanical failure, not operator error.