The Accumulative Nature of Aviation Accidents and Human Error

Key Insight

Commercial jetliner crashes rarely result from a single, dramatic mechanical failure, but rather from an accumulation of minor difficulties and seemingly trivial malfunctions. This pattern is consistent across virtually all industrial accidents, exemplified by the 1979 Three Mile Island nuclear near-meltdown. That incident began with a relatively routine blockage in a water filter, which cascaded into moisture leaking into the air system, inadvertently tripping two valves, and shutting down the flow of cold water into the plant's steam generator.

Subsequent failures at Three Mile Island included the valves for the backup cooling system being closed (for reasons unknown) and an indicator showing they were closed being blocked by a repair tag. Furthermore, a special relief valve in another backup system stuck open, and its associated gauge in the control room was also not working. No single major event caused the crisis, but five completely unrelated events occurred in sequence, each of which, had it happened in isolation, would have caused only a minor operational hiccup, but their combination brought the reactor dangerously close to a meltdown.

In typical plane crashes, several preconditions often combine: poor weather, time pressure (plane behind schedule), and pilot fatigue (52 percent of pilots in crashes have been awake for twelve hours or more). Additionally, 44 percent of the time, the two pilots have not flown together previously, affecting their comfort and coordination. The average accident involves approximately seven consecutive human errors. These errors are seldom about a lack of technical knowledge or flying skill; instead, they primarily involve breakdowns in teamwork and communication, such as one pilot knowing critical information but failing to convey it, or failing to catch another pilot's error.