Quote: From what I read/understand about his death, it was an accident, and it happened with Nefaria was getting away. I'm sure that Nefaria didn't care one way or another though, but it's like the whole Doctor Octopus and Captain Stacy thing.
What happened was this- Nefaria was escaping, Thunderbird jumped on the plane and started smashing it and the plane crashed as a result. It was mostly Thunderbird's fault.
Nefaria is somewhat snarky about it in his next Avengers appearance... it's entirely possible that he intentionally killed him to cover his tracks.