The Spyglass's flight assist will allow you to fly as high up as you want. It will accelerate above 100m and accelerate the more the longer you keep flying.
To turn the flight assist on or off, open the menu by clicking the "Menu" button, then go to Tools. Clicking the Flight Assist button will switch the flight assist on or off. The current state is shown in the dialog and in local chat.
Flight assist won't stop working if you power off your Spyglass.