You guys think too much...The plan for 9/11 evolved - its started as a job involving crop dusters. Atta was denied a loan to buy some cropdusters so he made the decision on his own to shift to hijack commercial planes and use them instead. OBL didn't care or even knew what was happening - he had other manage / take to fruition operational plans. Once the decision was made - the muscle was recruited / trained / and send to the US to assist in the operation.

BTW - OBL and company doesn't abandon an idea until it is made to work. In 1996 they tried to blow - up a plane using liquid explosives. They will not stop until they do it. We should be more concerned about preventing that than wasting time on why they didn't use an Airbus.