An embodiment of the present invention provides a blocking door that is pivotally disposed on a fixed nacelle of a tiltrotor aircraft for pivoting between a stowed position when a proprotor pylon is in the substantially horizontal position and a protective blocking position in front of the proprotor pylon when the proprotor pylon is positioned in the non-horizontal position. In other aspects, there is provided a blocking door and a method of reducing infrared and/or radar signatures of rotorcraft with a rotatable proprotor.