Aircraft engine nacelle with bi-directional ventilation system and related methods

Bi-directional nacelle ventilation and cooling systems (300) for use with aircraft (100) and related methods are disclosed. An example apparatus includes a passageway (302) to fluidly couple an opening (304) formed in a nacelle (202) of an aircraft engine (102) and an engine compartment (404) of the nacelle (202). The opening (304) provides an inlet into the engine compartment (404) when passive airflow is available to vent or cool the engine compartment and the opening (304) to provide an outlet from the engine compartment (404) when forced air is needed to vent or cool the engine compartment. A fan (508) is positioned in the passageway (302) to provide the forced air when the passive air is unavailable.