While out checking the orchards on one particular windy day with her dad, Sunny decides to try out a little tip her friend Storm told her about riding the air thermals during one of his flying lessons. These flying lessons are a secret btw. Unknown to her parents, Sunny had been taking a few flying lessons from Storm in secret. She’s still taking lessons from her mother for over a month now and hasn’t gotten anywhere other then being able to hover 3 feet off the ground. Storm wasn’t much of a teacher himself, he showed off more then taught but Sunny still learned more from Storm then her mother. But in all, she’s still only able to manage a wobbly glide.
 
So Sunny climb’s up on the fence and readies herself for a strong gust of wind. She doesn’t have to wait long when suddenly a huge gust of wind comes along and lifts her off the fence. Sunny flaps her wings likes crazy to try and stay upright. Big Mac just happens to glance over his shoulder and see’s his daughter being carried away by the wind. He gallops over to her and leaps up into the air and catches the end of her tail in his mouth and holds her from being carried away. He has a frown on his face but it quickly disappears when he hears his daughter laughing. Still being pulled by the wind like a kite she turned to her father while her little wings buzzed like a humming birds wings. “Did you see me daddy? I flew! I actually flew!” Her laugh was so infectious that Big Mac lets out a chuckle more so out of relief that his daughter was alright then her actually flying. Though not a pegasus himself he knew the difference from flying and being blown around by the wind like a piece of paper.
 
After this Big Mac decides it time to convince Fluttershy to let Rainbow Dash teach their daughter to fly.
 
Backstory of picture from the artist

@Poptard  
This

I take it as Mac realizing just how difficult it is to keep her under control, and as he just barely manages to catch her this time, it dawns on him his daughter is going to be a true wild child, flying everywhere at high speeds, pulling tricks, and defying death. And Mac is going to be sitting on the ground the whole time, able to do nothing but pray and pray harder to Celestia that it’s she won’t collide into that awfully large tree and break her neck and Mac will have to carry the body of his beloved daughter back to her mother…
 
So yeah, realizing a bunch of Parental Fear.

@wselfwulf
 
The kid’s trying to fly by catching wind gusts like a seagull. Big Mac is all “haha nope!”

@Background Pony #41CD  
well that’s what got from it

@wselfwulf  
Wrong.

That’s not a look of pride/joy on Big macs face, that’s a look of trying to betray pride/joy but is secretly thing “why oh why did I get her pregnant”