Thanks for the comments Chris. Yes, I added the noise on the first two - I thought it made them a little more interesting as images. I agree about the plane (a DH Dragon Rapide) being a little flat. I think the third image is the best of the three, and indicates how much more I've learnt about photoshop in the past few days!
I like the first one the most. It's looks like a candid reportage shot. The third one doesn't work as well for me because there isn't enough contrast for the selective colour to pop. The midtones are pretty bright in the shot so you could try doing a levels adjustment and moving the grey point slider to about 0.6 - that should give you a lot more contrast.
How did you do the conversion for the shot of the Rapide? It's possible you could get a lot more depth in the shot just by changing the way you convert to B&W