Fargoo,
It was the A320-100's I was referring to,took delivery of them in May 1988. I remember the airstairs well, unreliable as you say. De-activated after several "door open" indications in flight. Some of our newer A320's still have the 2 step ladder to nowhere under the floor boards in the avionic bay.
Were you BA engineering at LGW by any chance?
Apologies for the thread creep.