What might be different about an SLR for a PPL than for any other aspiring photographer? If size is an issue then the Olympus SLRs and mirrorless cameras are the ones to look at.
Otherwise all the main makes (includes Pentax, Nikon, Cannon, Sony, Panasonic) all have excellent offerings at various price points. Of course the more expensive cameras have not only more features, but more importantly better sensors which is an issue if you will be shooting in low light levels. They all have reasonable kit lenses.
Hope you are not planning using your camera whilst flying!