As an aside, many years ago a number of northwest aircraft used reverse thrust to back out of a gate, eliminating the need for a tug - certainly at Minneapolis when I was there in 1986. I think that this was only feasible with relatively low by-pass ratio engines such as JT8Ds used, on DC9 and 727s). It saved manpower costs but could result in higher maintenance costs and the introduction of higher by-pass ratio engines with the A319/320s and I suspect health & safety lead to the ending of the practise.