Mid air collision - not a possibility, since crash far apart.
Mistake at airport - in a universe of (put here the number of flights of the last 100 years) this happened 0 times. Probability : 0.000000....1%
Mechanics a few years ago put the wrong hydraulic fluid in a plane and it crashed. It does happen.
I never said it wasn't terrorism. I simply said there were other possibilities. Any good investigator considers all the possibilities and lets the evidence speak for itself.