“In an uncertain world, statistical thinking and risk communication alone are not sufficient. Good rules of thumb are essential for good decisions.”
Three minutes after taking off from LaGuardia airport in New York City, US Airways Flight 1549 ran into a flock of Canada geese. At 2800 feet, passengers and crew heard loud bangs as the geese collided with the engines rendering them both inoperable.
Gerd Gigerenzer picks up the story in his book Risk Savvy: How to Make Good Decisions:
When it dawned on the passengers that they were gliding toward the ground , it grew quiet on the plane. No panic, only silent prayer. Captain Chesley Sullenberger called air traffic control: "Hit birds. We've lost thrust in both engines. We're turning back towards LaGuardia."
But landing short of the airport would have catastrophic consequences, for passengers, crew , and the people living below. The captain and the copilot had to make a good judgment. Could the plane actually make it to LaGuardia, or would they have to try something more risky, such as a water landing in the Hudson River? One might expect the pilots to have measured speed, wind, altitude, and distance and fed this information into a calculator. Instead, they simply used a rule of thumb:
Fix your gaze on the tower: If the tower rises in your windshield, you won't make it.
No estimation of the trajectory of the gliding plane is necessary. No time is wasted. And the rule is immune to calculation errors. In the words of copilot Jeffrey Skiles: "It's not so much a mathematical calculation as visual, in that when you are flying in an airplane, things that— a point that you can't reach will actually rise in your windshield. A point that you are going to overfly will descend in your windshield." This time the point they were trying to reach did not descend but rose. They went for the Hudson.
In the cabin, the passengers were not aware of what was going on in the cockpit. All they heard was: "This is the captain: Brace for impact." Flight attendants shouted: "Heads down! Stay down!" Passengers and crew later recalled that they were trying to grasp what death would be like, and the anguish of their kids, husbands, and wives. Then the impact happened, and the plane stopped. When passengers opened the emergency doors, sunlight streamed in. Everyone got up and rushed toward the openings. Only one passenger headed to the overhead bin to get her carry-on but was immediately stopped. The wings of the floating but slowly sinking plane were packed with people in life jackets hoping to be rescued. Then they saw the ferry coming. Everyone survived.
All this happened within the three minutes between the geese hitting the plane and the ditch in the river. During that time, the pilots began to run through the dual-engine failure checklist, a three-page list designed to be used at thirty thousand feet, not at three thousand feet: turn the ignition on, reset flight control computer, and so on. But they could not finish it. Nor did they have time to even start on the ditching checklist. While the evacuation was underway, Skiles remained in the cockpit and went through the evacuation checklist to safeguard against potential fire hazards and other dangers. Sullenberger went back to check on passengers and left the cabin only after making sure that no one was left behind. It was the combination of teamwork, checklists, and smart rules of thumb that made the miracle possible.
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Say what? They used a heuristic?
Heuristics enable us to make fast, highly (but not perfectly) accurate, decisions without taking too much time and searching for information. Heuristics allow us to focus on only a few pieces of information and ignore the rest.
“Experts,” Gigerenzer writes, “often search for less information than novices do.”
We do the same thing, intuitively, to catch a baseball — the gaze heuristic.
Fix your gaze on an object, and adjust your speed so that the angle of gaze remains constant.
Professionals and amateurs alike rely on this rule.
… If a fly ball comes in high, the player fixates his eyes on the ball, starts running, and adjusts his running speed so that the angle of gaze remains constant. The player does not need to calculate the trajectory of the ball. To select the right parabola, the player's brain would have to estimate the ball's initial distance, velocity, and angle, which is not a simple feat. And to make things more complicated, real-life balls do not fly in parabolas . Wind, air resistance, and spin affect their paths. Even the most sophisticated robots or computers today cannot correctly estimate a landing point during the few seconds a ball soars through the air. The gaze heuristic solves this problem by guiding the player toward the landing point, not by calculating it mathematically . That's why players don't know exactly where the ball will land, and often run into walls and over the stands in their pursuit.
The gaze heuristic is an example of how the mind can discover simple solutions to very complex problems.
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The broader point of Gigerenzer’s book is that while rational thinking works well for risks, you need a combination of rational and heuristic thinking to make decisions under uncertainty.
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