The anorak in me insists on trying to grab a shot of everything I fly on (don't know why, I just do)
My system is as already stated, have the camera ready to shoot and just go for the shot as if your just a tourist, IF someone objects dont argue just nod, drop the camera to the hip and carry on shooting discreetly. Shooting "from the hip" is a recognised technique that pros use in sensitive situations and with practice can give good results. A wide angle lens and keeping the shutter pressed will give you a better chance of getting the shot.
If you know it's going to be a no-no such as in Doha or Dubai just go straight from the hip.
Works for me !