AirFoil self check failing - ZIBO B738-800 modified - X-Plane.Org Forum So when i load up on X-Plane 12, a message saying "Airfoil self-check failed: You entered ZERO LIFT SLOPE... for a foil that HAS LIFT! This is impossible! This makes Austin guess at lift intercept for 3aD foul efects, which is a less accurate simulation! Aircraft/Laminar Research/B737-800X/b738_4...