Originally Posted by Kickstart
..is it true to say that if an aircraft does not have enough air speed then it will get into difficulties (stall) on a downwind turn..?
Not exactly. If the plane has enough airspeed to maintain straight and level flight it should be able to execute a downwind turn without stalling. The problem is that if the margin is small and the turn is not made carefully a stall is likely, because when the wing is banked for the turn some lift is lost.