The Boeing product line is thus a family of families, all sharing a consistent design philosophy that produces additional commonality between families. Two basic factors encouraged Boeing to use the family approach in developing the most complete product line in commercial aviation. The first is customer preference. Airlines find that when they get their airplanes from one manufacturer that offers a comprehensive product line, it saves them money every day. Obtaining parts is less complex and expensive, and faster, as well.
Mechanics can use many of the same tools and procedures across a variety of airplanes.
Perhaps most important, flight and cabin crews are always in a familiar environment, helping them do their jobs efficiently on every plane in the fleet. And, especially for flight crews, a consistent flight-deck design philosophy makes it easier to transition between families. The second factor is safety. The Boeing flight deck helps crew members communicate with each other and for the flight control system to continually communicate with them. Crew awareness is the heart of flight safety and the consistent focus of Boeing flight-deck design.