Since you are a businessman, I'm going to be direct:
a) You were fighting an uphill battle right from the start because you took this photo at probably THE absolute worst time of the day to take such a shot, ie, on a clear day with the sun high in the sky. To make matters worse, you took it from the shadow side of the plane. This decision essentially forced you to make some fairly major adjustments in PS to deal with the resulting high contrast and deep shadows.
You did a pretty good job working around this problem, but images made with major post-processing (aka, PP) adjustments *never* look as good as getting a good image right at the start, in your camera. Forget the really interesting possibilities that would open up if you had shot around dusk with supplemental lighting, but, if you had done nothing more than positioned things so that you could shoot from the sunlit side of the plane, there would immediately have been vastly more "pop" in your photo. FYI, I've attached a copy of one of my photos from a shoot for an Annapolis publication of midshipmen training in a glider. Notice, in this photo, I didn't try to shoot into the sun.
b) In your photo, the viewers' eyes are not led to where you want them to be, ie, on the plane, and especially, on the cover you are trying to sell. There are several reasons for this. First, there is way too much detail and texture in the sky and on the ground, and because the viewer can see a bit of the hanger under the belly of the plane -- the viewers' eyes keep getting pulled to these areas.
Second, there is a pale blue/cyan color cast over just about everything in the image, so there are no good color contrasts to help guide the viewer's eyes. Part of the reason for this is because on a day like this, shadows will always have a blue cast because these areas are receiving their illumination from the blue sky, not the yellow sun. Below, I've also attached a little quick and dirty demo that shows the beneficial effects of minimizing the overall blue cast to provide color contrast (not just brightness contrasts) in your image. This little example introduces it's own problems (eg, 1 second masks ;-) ), and certainly does not purport to address all of the problems with the image, but is just to suggest how better color correction generally gives more impact / pop.
c) With respect to the post processing you did, in addition to there being too much detail in the sky (which I suspect you added or enhanced), there are also various odd pixellated and streaked areas in the sky. Also, the edge between the plane and the sky (and other background elements) was done poorly, so it left this odd boundary -- soft and with a dark halo in areas. Both of these issues might seem to be minor, but I can assure you that they really will detract from an overall impression of quality, and "pop" to the image.
If you want more details about my suggestions, don't hesitate to ask.
Best regards,
Tom
Attachments:
1. For immediate reference, here is the photo part of your advertisement (down-rez'ed for in-line display):
2. Same as #1 except simplified the sky and removed the overall blue cast in order to provide color contrast against the blue cover.
3. One of my shots from a shoot for a USNA publication showing midshipmen training in a glider. I put the sun to my right, instead of in front of the camera, to intentionally give plenty of "pop" and a feeling of depth to the photo. (Note: putting the sun in this position isn't something I would recommend for a portrait -- unless you also used a fill light).