In the old days, when centering was often discussed here, I liked to talk about the 'weight' of the parts of the photo. Centering is not about counting pixels from the extremes of the subject to the edge of the frame, but about putting the 'centre of gravity' of the photo in the middle.
The helicopter fuselage has more 'weight' than the long slim tailboom or the rotor blades. Therefore the tailboom and blades should ideally be put closer to the edge than the fuselage, putting the fuselage more in the centre, such as here.
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Photo © Peter de JongView Large View Medium
Photo © Peter de JongView Large View Medium
Photo © Peter de Jong
I agree with Colin that including the entire rotor is much better in this case, but I would still consider the 'centre of gravity', so I'd put the top blade close to the edge and the fuselage more in the middle.
So I don't think either of your crops is actually well centered. In the second, you also cut the front blade right through the tip, which doesn't look nice.
The screeners usually allow quite a lot of liberty in cropping helicopter shots, but I think this might be helpful.
Peter
