I had to hire someone to look after my son when I'm flying (LH too). She comes home and sleeps here if we're away (dad's a pilot like in your case). He's spent every Summer since he was born with my parents who move seaside from June to September.
I'd find very difficult to spend 9 days in a row away, especially when the child is very little. In my experience, after 3 days they find it hard and start asking for Mum even if they're with Dad or Gran. I think I'd go for the 5+5 option.
Good luck
