[Stiglr]

Actually, I don't think Merge will work, since it's altogether possible to have one object contain a couple of pieces that aren't one contiguous piece. So use either the Convex Object or extrusion strategies to mate them up. Go to Vertex mode, select the Vertices on the ends of each piece where they should meet, and then do the Convex Object; see what kind of "joint" you get. My predicition is that it'll be "messy", and not conducive to a smooth fuselage unit. Extruding from the yellow piece I think will be the best course of action. That purple area doesn't seem like it'll be too hard to recreate. You might want to Lock that, so that the outline of its shape is in view as you work, but you can't inadvertently select it or have it get in the way. Or, just reshape the area from your viewport background 3-views.