Originally Posted by
beatnik
Don't know if the aircraft is shielded or if the shape of the fuselage requires that you need an external aerial (as aircraft have)
Perhaps someone can shed some light for me?
Yes.
The aircraft fuselage is effectively a "Faraday cage" (see Google for more detail) that prevents radio signals from passing. The windows leak a bit of RF through, so holding your radio up against a window will allow some reception.
But as said above, the local oscillator in your receiver may interfere with the aircraft equipment. Or it may not, but I wouldn't risk it.