Hi all, I have a couple of flights coming up, short haul MAD - LHR and Long haul MAD - MEX and wondered if there is any system to how seats are allocated by the computer if you don't pay for one, or if it's completely random?

I suppose specifically I was wondering:

- does it fill from back to front or front to back as check in progresses or neither?
- does checking in early have any impact, are you more likely to be seated in a particular area, or could you still be in a middle seat at the back?
- will they put solo travellers in window/aisle seats as long as these are available?

I'm interested not just to know the outcomes of not paying for a seat, but I was also wondering if I do pay for a seat, where I might be more likely to get an empty seat next to me. Normally this works best at the back, but if the system fills from the back then obviously actually the front may be better.

I'd be interested in your experiences, thanks.