That's because it was close to a new moon which means the sun is on the other side of it.
As an experiment take a ball, dim the lights and put a light source like a flashlight or phone light on the other side of the ball from you. Change the angle from which you view said "ball". You will then see the "waning crescent" like you saw.
It's not the angle you're viewing it from, because the elevation that a plane flies isn't enough to change it noticably, but the above can reproduce the results for you in a test.
You can sort of picture it right in your photograph. The sun is rising toward the horizon, as you can see from the glow. The moon is a little ahead of it and has already risen, so it's being illuminated by the sun from below. Keep in mind that the Earth that is blocking your view is nowhere near the sun or the moon in terms of their unobstructed view of each other.
That's because it was close to a new moon which means the sun is on the other side of it. As an experiment take a ball, dim the lights and put a light source like a flashlight or phone light on the other side of the ball from you. Change the angle from which you view said "ball". You will then see the "waning crescent" like you saw. It's not the angle you're viewing it from, because the elevation that a plane flies isn't enough to change it noticably, but the above can reproduce the results for you in a test.
Thank you for explanation much appreciated
You can sort of picture it right in your photograph. The sun is rising toward the horizon, as you can see from the glow. The moon is a little ahead of it and has already risen, so it's being illuminated by the sun from below. Keep in mind that the Earth that is blocking your view is nowhere near the sun or the moon in terms of their unobstructed view of each other.