Sounds like you need a new job.
Putting a request in 4 months away and possibly being denied is insane. I can call off anytime I want and have someone flown in to cover me. One time I was denied a full day off, and only given a half day and almost quit over that.
But I do work alone and calling off a day prior isn't the best solution for anyone..
I would tell him flights paid for, you approved it. Either fire me over it or I'm taking the time off