Many children dream of flying a plane when they grow up, and being a pilot is often considered to be one of the coolest jobs in the world.
If you ever tried to do something difficult without knowing how you could say you're "flying by the seat of your pants." This expression comes from the early days of flying when planes didn't have much equipment to show the pilot where to go. It meant to fly a plane without the help of special equipment, such as a radio.
For example, if you had to take your friend to hospital but didn't know how to drive a car, you might say, "I can't believe we got here, I was really flying by the seat of my pants!"
If someone goes past the normal limits of something, usually to do something new or dangerous, you can say they are "pushing the envelope." This expression became known because of pilots that tested new planes. They would try to find out a plane's "flight envelope," which are its limits for things like how fast and high it can go.
So if you drove much faster than what was safe to get your friend to the hospital, they might say, "You were really pushing the envelope driving that fast."
If you think something will never happen, you can say it will happen "when pigs fly." This expression comes from the 1600s when people would sarcastically say "pigs might fly" if a person thought that something impossible might happen.
So if you offered to drive your friend home from the hospital when they're better, they might say, "I'll get back in a car with you when pigs fly!"