I want to disagree slightly with my esteemed colleague, Screener2. (Screener fight!)
All I want to say is that I don't think this pic *can* be rescued, at least not without a rescan of the original. The reason for that is that I think it has been sharpened as much as possible (maybe slightly too much so) already - looking at the Northwest titles and the windows suggests this. However, at the same time, the US flag on the fuselage is completely indistinct, and the Northwest logo on the tail seems very soft.
I have tried very gently applying some unsharp mask to the image, but it seems to have made things worse. My suggestion would be to go back to the start & rescan the image from scratch, and then as S2 suggests, crop the image so the aircraft is centered. You may need to adjust your scanner settings to get a better result.