The luxury of the Golden Age of air travel is still alive and well in the first-class cabins of the world's leading airlines.

But the de Havilland Comet’s success was short-lived. A fatal design flaw, hidden in plain sight, turned square windows into a deadly weakness. Cracks formed, pressure built, and tragedy followed.

In the event of an airplane accident, the flight recorder provides data that is invaluable for clarification. The device was ...