The Montreal Convention didn’t require Jennifer Moore to prove negligence by British Airways when, disembarking at the end of a Boston to London flight, she fell taking the last step off a mobile staircase. Under Article 17(1) of the treaty, all she had to prove was that her injuries were caused by an “accident.” Each step down the staircase was 7.4 inches, except that the gap to the ground for the final footfall was 13 inches. Because the ground was “further down” than she expected, Moore was thrown off balance and …