Early aviators had a system of radio signals to guide pilots through fog and bad weather.
Dots and dashes were beamed out from a landing field and picked up in the pilot’s earphones.
If he heard dot-dashes, he was too far left, and dash-dots meant he was too far right.
But when the signals converged into a continuous buzzing sound, the pilot was “on the beam,” or safely on course.
An instrument landing system, or ILS, is a ground-based instrument system that provides precision guidance to an aircraft landing on a runway, and uses a combination of radio signals and lighting in low visibility.