Complex sentence: Additionally, the handle moved a metal plug into a vent cut in the outer hatch panel: if the vent was not plugged the fuselage would not retain pressure, eliminating any pneumatic force on the hatch.
Split into simpler sentences: Additionally, the handle moved a metal plug into a vent cut in the outer hatch panel. If the vent was not plugged, the fuselage would not retain pressure, eliminating any pneumatic force on the hatch.