The composition is okay, but the lack of lighting makes it look static and flat.  You need to add shadows and highlights from the light's point of origin, in this case the sun.  Also, the color of the lighting on the plane has to match the color of the lighting and shadows on the clouds.  I've quickly made these edits to the picture; the shadowing isn't perfect, but should give you an idea of how to add depth and make the planes look less out of place:



You can download the psd here.  I hope it helps.