Once the speed brake is extended, what action will not retract it?

When the speed brake is extended, the action that will not cause it to retract is extending the flaps. This is significant because the flight control systems are designed in such a way that extending the flaps allows for increased lift and drag, often requiring the speed brake to remain extended to manage aerodynamic forces effectively.

The retract mechanism for the speed brake is typically influenced by the other actions mentioned. Moving the power control lever (PCL) to idle engages certain aerodynamic efficiencies that lead to retraction, as does moving the speed brake switch forward, which is a direct command to retract it. Additionally, applying brake pressure often signals a reduction in speed or descent rate, which may also lead to the retraction of the speed brake. Therefore, since extending the flaps does not provide a retraction command to the speed brake, it is the correct response to this question.