Recently, I have had several photos rejected for quality being below current standards. The rejection notice says the following:

Quality:
The photo is of overall lower quality than our current standards. There may not be a particular issue which we can point out to be corrected, but rather lower quality overall.

Here is an example of one of the photos that was rejected. It appears to me to be a perfectly fine shot...The color seems good, it is centered both vertically and horizontally, it is sharpened (but not overly so) and shows the entire aircraft. There does not seem to be any heat haze or distortion either. So, why the rejection? And is it possible to appeal the decision somehow? This is a great site, and I try my best to submit quality shots. There have been some that I admit were less than stellar, and I usually knew they were borderline when I submitted them, but this one in particular is NOT one of them.

I appreciate the help.

Aaron

This picture does not look too bad to me. Sailingdutchman may be right on sharpness. In the rejection email, that you received' the reason is given. But maybe one of the screeners can step in and give some further explanation.
But as stated; rejections happen to us all. I try to learn from the comments in the rejection emails. It has helped me to improve my post processing.