2.
At the start of any program, asking questions is the most important part of the process. If you get [the customer's] requirements wrong, then you don't have a successful product.
Joe Sutter
3.
. . . It wasn't until the jet engine came into being and that engine was coupled with special airplane designs - such as the swept wing - that airplanes finally achieved a high enough work capability, efficiency and comfort level to allow air transportation to really take off.
Joe Sutter