 However, the auxiliary power unit was initially optional, rather than standard, equipment.The wing has 13 degrees of wing sweep with a supercritical airfoil optimized for cruise flight at Mach 0.78.Though there are no leading-edge slats or wing fences, the wing has vortilons on the leading edge, to avoid spanwise flow, and small metal triangles on the leading edge to minimize airflow separation during flight at a high angle of attack.