I'm sure the answer is "it depends", but which airline allows for the most schedule flexibility? I admittedly know nothing about the airline scheduling process, but how hard is it to add/drop trips? For example, if I'm scheduled for a Mon-Thur trip, but my kid has some school shit that my wife wants me to attend on Wed, can I drop the trip and it's easily picked up by someone else? Do I need to find my replacement? Or do I need to put in for a day off months in advance and hopefully the chips fall my way?