Flex takeoff is permissible when anti-ice fluid type 1 or IV is present on what part of the aircraft?

The correct answer is that flex takeoff is permissible when anti-ice fluid type 1 or IV is present on the wings of the aircraft. This is crucial because the wings are the primary surfaces responsible for generating lift during takeoff. The presence of anti-ice fluid on the wings ensures that any potential ice or snow is effectively inhibited from forming, which could lead to reduced lift or aerodynamic performance issues.

While anti-ice fluids may be applied to other areas of the aircraft as well, the specific concern during takeoff revolves primarily around the wings, where any contamination from ice or snow could significantly impact flight safety. The fuselage and tail do not play as critical a role in lift generation during the initial phases of flight. Therefore, the presence of the fluid on the wings is what makes flex takeoff permissible, ensuring that the aircraft operates safely and efficiently under potentially icy conditions.