I got the Add-On package #3 a couple of days ago. I then selected the B-17 and replaced the OS 52 4-stokes with 43 lb. AMT turbines! The plane gets to 400 mph and then starts all over again from 0 mph. The plane actually (not just the numbers on the screen) stalls and then stars to pick up speed again. Must be a limitation of the program. Try it, it is very fun!!