No Voodoo It is called reverse engineering. We use information from many sources; Real FDR data, Performance engineering manuals on both aircraft and engine (the real engineering stuff, not regular pilot operating manuals), and many hours in the big full motion simulators testing edge of the envelope situations. Finally, we have our real 737CL pilots do quality assurance tests on the feel and numbers inside the envelope. We have also "tuned" XP's flightmodel in many areas to get where we want. So we know (and can prove) that we are extremely close inside the envelope, and very close on the edges. Together with XP's superior flightmodel, this will give you a very unique experience handflying this aircraft. And actually, it will also dramatically improve realistic operations on autopilot. Your vertical profiles on climb and descend will be very realistic, engine performance in the entire envelope etc. So the "voodoo" is a combination of having the best information available, engineers that can understand it, programmers that can code it, and pilots that can test it, and offcourse the best sim platform M