Before going to our aeroplane, let's explain the general idea of the process:
1. The object must be divided in simpler components. In our case: fuselage, wings, fins, tailplane and turbines.
For each one of these components, we must:
2. Build the approximate cross-section (see "Front" in the left image).
3. Using the side plan as the background image, extrude the circle, and grab and scale it following the outline (see "Side").
4. Now with the top plan as the background image, select successively each cross-section, and grab and scale it again, but now RESTRICTING the movement to the X axis (see "Top").