As for the color of the sky, as someone already mentionned, it is clear when you look up, but not when you look toward the horizon. We can see a lot of atmospheric perspective ( that is, the humidity, pollution and everything) between you and the background (the buildings). That atmospheric perspective, which is gray in a polluted city, is much more deep in the area just above the horizon, because it extends way further, so it gives a grey sky such as this. You have to shoot on a very very very clear day not to see it in a city.
But for the grain, your problem seem to come, in my point of view, from a contrast too high. You lose all the detail in the dark (for example the fan of the engine) and clear (the white part of the plane's fuselage) parts of the picture. You probably had way more detail in these areas on the original picure, straight out of the camera. If not, the camera itself shoots with too much contrast. You could probably set it to a lower value.
(Sometimes, the light of the day gives too much contrast that the dynamic range of the film (or in this case the ccd) cannot fully render. I don't believe though that we can account for such a high contrast only caused by the type of light you had. Usually, days that give such high contrasts don't have as much atmospheric perspective as you have on your picture.)
When you add more contrast to the entire picture (eith an image editing software), it most of the times results in a granier picture, because you increase the contrast between the "grains" and their surroundings, hence you see them more. So my advice would be to try different contrast values. If you have Photoshop, work with the curves in an adjustment layer, so you can always change the settings.