Bad Jokes and 9/11 Planes

This is a dark joke that compares bad jokes to the planes used in the 9/11 terrorist attacks. The punchline is that the jokes don't "land" meaning that they do not come across well or are not funny, just like the planes in 9/11 did not land safely. The humor is derived from the dark and unexpected comparison of something lighthearted (a bad joke) to a tragic event.