Wirestock/Getty Images Since it first flew in 1967, the Boeing 737 has been one of the greatest success stories in commercial aviation. With a small, narrow-body (a single aisle between the seats) plane with short- to medium-range, it was perfect for flights of just a few hours in length, which covers the majority of domestic routes. That led to thousands of these aircraft being delivered, making it the most popular plane in the world. In fact, at its peak, nearly a third of all flights were flo...