Everything heera said! I always try book an overnight flight or break his sleep and do an early morning one. I did an overnight with my son and he slept through the whole flight.
Everything that you know soothes him (that is allowed on the plane) bring it with you just in case. Some babies do better than others. Bring an empty bottle/sippy cup with you and request some juice or water for him as the plane goes up and as it descends bcuz some babies will feel the popping in their ears and thats when they start to cry and are uncomfortable. chewing gum helps but he is too young to chew the gum and not swallow it. Other than that I’m sure he will do great!! Some babies I’ve seen not even budge lol❤️💎