Photographing out of an airplane requires a fast shutter speed to overcome the vibration of the plane. You don't need to use small lens apertures for depth of field because everything is relatively far away, and the landscape or cityscape will be in focus at any lens aperture (assuming you are not including the wing of the plane). Therefore, I shoot wide open, or perhaps one or two f/stops down from wide open for maximum sharpness, and my shutter speed is at least 1/1250. I prefer 1/2000 if there is enough light and I don't have to raise the ISO too much.
The picture I've attached here shows the famous statue of Christ the Redeemer in Rio de Janeiro, Brazil. I shot this from a helicopter with the door taken off to maintain the best quality possible. I waited for good lighting on the statue before I hired the chopper. I took this about an hour before sunset, and I made sure that I angled the camera downward to avoid including the rotors in the picture.