Hi Alexander,
I've no idea what would happen to the plane but I want to comment on your son. I think it is wonderful that he has asked such a question to you. To me it shows imagination and willingness to learn and with those two things he will go far.
My youngest son, Lucas, is a bit like that. A few months ago he asked me "Dad, if we stretched the Earth out till it was the size of a piece of string, how long would the string be?"
I loved this question and it was a great oopportunity to show hm that maths is important and does actually have some uses. We made some assumptions (the string would be 1cm in diameter, the earth was spherical with 12,756 km diameter) and used very simple maths formulae to determine the answer. He was really engaged by it.
Your son may like the 'Wait, But Why' website if you haven't heard of it already. Lots of great hypothetical stuff on there to engage an inquisitive young (and older
) mind.
Cheers,
Dan