I have a book called The Lateral Logician by Paul Sloane & Des MacHale.

When I was teaching workplace communications at an adult learning college I used to throw one of these puzzles at the class members at the end of a lesson because it encouraged questioning, searching for facts and information, using logic and working together to find the answer. They could ask Yes/No questions.

This is one of the first puzzles in the book, in the easy section.

1.2 Bombs Away
"One night during the Second World War, an allied bomber was on a mission over Germany. The plane was in perfect condition and everything on it worked properly. When it had reached its target, the pilot ordered the bomb doors opened. They opened. He then ordered the bombs released. They were released. But the bombs did not fall from the plane. Why should this be so?"