A hurricane sounded okay at first but there are two problems: Gertrude would be blamed for her actions, and hurricanes dont dissipate when they hit a plane. She also wouldnt enter the plane. A bird would probably be blamed, too, unless the question really wants to be stupid by saying "No one ever knew a bird caused the crash." She also wouldnt enter the plane, unless she entered and began attacking the pilot...Lol unlikely. But a lake sounds the best suiting, "Lake Gertrude" The pilot crashed into Lake Gertrude, the water seeped in and drowned everyone and wouldnt be blamed because it's the pilots fault for crashing. Then again, a lake is inanimate so it cant cause its own death.