Redundancy, Rationality, and the Problem of Duplication and Overlap

N OT SO LONG AGO I experienced an emergency landing. We had been aloft only a short time when the pilot announced some mechanical failure. As we headed toward the nearest airport, the man behind me, no less frightened than I, said to his companion, Here's where my luck runs out. A few minutes later we touched down to a safe landing amidst foam trucks and asbestos-clad fire fighters. On the ground I ran into the pilot and asked him about the trouble. His response was vague, but he did indicate that something had been wrong with the rudder. How, then, was he able to direct and land the plane? He replied that the situation had not really been as ominous as it had seemed: the emergency routines we had followed were necessary precautions and he had been able to compensate for the impairment of the rudder by utilizing additional features of the aircraft. There were, he said, safety factors built into all planes. Happily, such matters had not been left to chance, luck, as we say. For a commercial airliner is a very redundant system, a fact which accounts for its reliability of performance; a fact which also accounts for its adaptability.