You can also find out the airline you thought you were going to fly with has subcontracted the entire flight to another carrier.  Norwegian Air did this to me last March so I got the privilege of flying with a Spanish company I'd never heard of....old plane, worn out seats, etc. I'd wouldn't't have booked this airline in the first place but wasn't warned of this or else would have rebooked.   So Norwegian Air you lost me for good.....