Use manual mode and manual focus. Raw mode if you know how to use processing software. Prefocus at infinity or a touch short of infinity.
For an idea of settings, the photo below was with the FA 43, 1/90 shutter, f2.0, ISO 3200.
Buy a collapsible rubber hood that screws in like a filter. They are inexpensive. You can press the hood against the glass to block interior reflections. Flexible rubber lets you aim the camera while maintaining the seal. Keep the lens close to the window to hide dirt.
The ideal time to snap shots is during a sharp turn towards your side of the plane. That lets you aim downwards yet shoot perpendicularly through the glass. You might even be able to see the ground if you are stuck seated above the wing. Pay attention to what the plane does during takeoff and landing.