English: Since it first entered the NASA inventory in 1974, NASA 515 has been a testbed for research into a multitude of issues affecting aircraft safety, efficiency and capacity. It goes beyond the typical research facility in that it demonstrates new concepts in real-world situations. The aircraft has been modified to include a second flight deck positioned behind in what was the aircraft's first-class cabin section. In addition, the B-737 has rows of computer consoles and data collection stations where researchers monitor real-time flight results. This picture of the cutaway model of the B-737 shows the general layout of the aft flight deck and the research stations in the aircraft.