there's something not quite right with your contrast and colours. The whites are so bright they make my teeth hurt, but they don't seem really WHITE, and the colours seem dark and muddy. Perhaps this could be improved by toning down the colour saturation some, reducing the contrast a little, and then tweaking the overall colour balance to either reduce the red a little or increase the blue. If the original is too yellow, this can also be fixed by a boost to the blue element.
looks to me like the problem is a slight lack of crispness. There's already a little grain there, so sharpening is only going to worsen it. I just tried running it through the sharpen filter, and this improves the aircraft, while making the sky too grainy, so perhaps you could mask the sky and just gently sharpen the plane, enough to crisp it up a little, without adding jaggies.