Complex sentence: Rocky and Ginger finally grab onto the string of lights which was caught on the plane's landing gear as the plane departed, but Mrs. Tweedy soon awakens and grabs the lights, which weighs down the chickens' plane.
Split into simpler sentences: Rocky and Ginger finally grab onto the string of lights which was caught on the plane's landing gear as the plane departs. However, Mrs. Tweedy soon awakens and also grabs the lights, which weighs down the chickens' plane.