‘Pitch’ is a word that has a lot of different meanings in English, but I think three are relevant here: • It can mean the steepness or incline of a slope (usually a roof), which I think is what you mean when you say level. Eg: The roof isn’t flat, it has a very steep pitch so that rain runs off it easily. This isn’t what it means in the example you shared though • It can also mean the swaying or movement of a ship or an aircraft. Eg: the ship pitched back and forwards on the large waves during the storm. It has the sense that it’s making things unsteady and possibly a bit dangerous. It’s not a gentle movement. I’m not sure this is quite what your example is saying either • It can also mean to move forward and down very suddenly. This is what I think it means in your example. A plane could pitch in an emergency, meaning it starts falling towards the ground nose-first. Hope that helps!

Because a plane flies in three dimensions there are different words for how it moves off a straight line: like pitch, roll, yaw. I think pitch means going up and down like on a rollercoaster but not sure.