Qatar Airways

This is a very common problem. For a try avoid JPEG Compression it is necessary to allow as little treatment as possible to the sky and keep a certain amount of noise. I recommend using a different degree of noise removal for the sky and everything else.

To remove noise, it is better to use the free plug-in Dfine2 or paid plug-in Topaz DeNoise

David, I don't know in what way you save your photos, but always remember to use option "save for web", with the highest quality (maximum and 100%) and make sure that all three options (progressive, optimized and embed color profile) are unselected. That should help you with a jpg compression rejections.

And for grainy sky, I also would recommend you Dfine2, because DeNoise generally generates more banding (but it has also stronger algorithms). Instead Dfine2, you can use simply noise reduction in Camera RAW filter. To make sure that your sky is "clear", use option "equalize" in Photoshop (the same function you use in order to find dust spots). When the colours are equalized, you can easily check amount of noise in sky.

grainy film shots are accepted. I see no reason why noise in digital shots should not be accepted. Within reason