A helicopter was flying around above Seattle when a malfunction disabled all of the aircraft's navigation and communications equipment. Due to the darkness and haze, the pilot could not determine the helicopter's position and course to get back to the airport. The pilot saw a tall building with lights on and flew towards it, the pilot had the passenger draw a handwritten sign reading "WHERE AM I?" and hold it up for the building's occupants to see. People in the building quickly responded to the aircraft, drew a large sign, and held it in a building window. Their sign said "YOU ARE IN A HELICOPTER". The pilot smiled, waved, looked at his map, determined the course to steer to SEA-TAC Airport, and landed safely.
After they were on the ground, the passenger asked the pilot how the sign helped determine their position.
The pilot responded "I knew that had to be the Microsoft support building. They gave me a technically correct but entirely useless answer."