Complex sentence: Escape slides are packed and held within the door structure inside the "slide bustle", a protruding part of the inside of an aircraft door that varies in size depending on both the size of the aircraft and the size of the door.
Split into simpler sentences: Escape slides are packed and held within the door structure inside a slide bustle. This is the protruding part of the inside of an aircraft door and varies in size depending on both the size of the aircraft and the size of the door.