UA752: Also I have noticed that on lots of jets that the metal directly below the door is not painted...why is that?
Another possible explanation is given here: http://www.concordesst.com/model102/pop9.html
I don´t know if this problem is also relevant on subsonic planes; But helicopter rotors are known to pick up static electricity while they are moving through the air.
So this unpainted area below the airbus door might be used to discharge the fuselage in a controlled way in order to spare an unsuspecting passenger...
Seems a little small for mechanical protection.
Do jetways usually have brush contacts in this area?