The altitude range arc, or “banana” as many users call it is a very useful tool in Infinite Flight, seen here. It extends out from the pilot’s aircraft icon on the map.
The arc’s main function is to represent the point at which the aircraft will hit its set altitude that you set in autopilot. It’s position is determined by both the speed in ground speed and vertical speed of the aircraft. And keep in mind that ground speed factors in wind, and wind speed changes with altitude changes.
The “banana” is a feature that is often looked over. It can give you a greater understanding of how well your ascending or descending, giving you even more information to use to make changes mid-flight.