But how did they keep flying without anyone in the engine room? Plothole?
I'm going with 'it was just a few minutes: the engine didn't have to overheat and the fuel didn't have time to run out'.

I don't care how deus ex machina this was, either. For me, it's like this shows it wasn't about all that Guru crap, but the Avatar State is related to energy. Katara did say in 3x01 that he had some knots in the back or something -blocked energy, in other words. That hit looks like what acupuncture or shiatsu are meat to be like: free energy through the body, unblock whatever chakra was blocking the Avatar State. I don't know, it makes a lot of sense in my head, Asiatically speaking.
And the other Avatars had told him that attachment was good in his case.
You know, some people are saying Aang didn't sacrifice anything but he did sacrifice spiritual enlightment. So he got a girlfriend in return, but Aang is still a monk and that must've hurt.

I don't think it was a pussy, children's cartoon solution not to kill Ozai. Taking away the power from a man who thought to be the most powerful one in the world, and leaving him alive afterwards, seeing the glory accomplished by those he underestimated as weak. That brings him more pain and humiliation than a death in battle in my opinion. For such a man it's a more terrifying punishment than dying in the spot. Besides, children's show or not, it's more like Aang to end everything like this. It's justice and peace.
Maybe I'm a stupid hippie, but death is mostly never the answer. Not killing him showed that Aang was stronger than Ozai, not that he was weaker.