There’s 20M lightning strikes per year in the US according to a quick web search, with the vast majority of those happening in Florida and very few on the west coast.
Let’s assume west coast flights don’t apply, only ones in the SE United States. Even then, you could maybe be “lucky” enough to get one strike per day.
Doing some very rough napkin math, a lightning bolt can provide ten billion watts of power, but for something way less than a millisecond (most sources I’ve seen say closer to a nanosecond, but let’s be optimistic and go with 1/1000th). Assume we have the ability to buffer this (we don’t, to my knowledge), that gives us 10MW for one second assuming 100% efficiency. A 747 takes 90MW of power just to get airborne and it needs that for longer than a second even for that. So basically you’d need something like at least 100 lightning strikes just to get the 747 airborne (assuming that’s doable in 11ish seconds, I think it “might” in extreme circumstances).
I’m sure my math is grossly flawed in some way, so don’t expect scientific accuracy at all, but it should clearly show the absurdity of using lightning as a power source for jet flight.
Free power?