 The Boeing 727 also used a mix of inboard Krueger flaps and outboard slats, although it had no engine between them.Most early jet airliners, such as the Boeing 707 and Boeing 747, used Krueger flaps only.While the aerodynamic effect of Krueger flaps may be similar to that of slats or slots (in those cases where there is a gap or slot between the flap trailing edge and wing leading edge), they are deployed differently.