How Psychology Helped Design Safer Airplanes

The B-17 Flying Fortress was one of the most successful bombers of World War II but suffered a fatal design flaw that created a new discipline that incorporated psychology into aviation design.

Airwolfhound I Wikimedia Commons

The Fatal Flaw of the Flying Fortress

The B-17 Flying Fortress dropped more bombs during World War II than any other American aircraft (Apple, n.d.). The fearsome heavy bomber was a marvel of engineering with crews admiring its remarkable toughness and survivability (Kuang, 2019) while being feared by its enemies because of its many defensive guns and heavy bomb load (Leone, 2023; Apple, n.d.). Mysteriously though, this sturdy plane with combat-hardened crews kept having an increasing number of accidents and crashes when returning to base (Galotti, 2008).

Thousands of reports piled up and made their way to a young psychologist who soon discerned a clear pattern: While these accidents were considered a result of “pilot error”, they were not random—which would indicate that unsuitable or unqualified pilots were being recruited (Kuang, 2019). Instead, there were hundreds of crashes because pilots either landed without deploying the landing gear or retracted the gear soon after landing (Kuang, 2019; Lachman et al., 1979). How could highly experienced and trained aircrews after returning from a combat mission make such rooky mistakes?

Flight-deck of a B-17.

Source: Eric Ward | Unsplash

After looking deeper into these mysterious accidents, a fatal flaw in the design of the B-17 was discovered: The landing gear and the wing flaps were controlled by two switches that looked identical placed right next to each other (a closeup image of the switches can be found here). Hundreds of pilots accidentally actioned the flaps instead of the landing gear, landing without the gear deployed (Kuang, 2019). It is standard procedures to retract the flaps after landing. Many further accidents occurred when pilots retracted the landing gear instead of the flaps (Lachman et al., 1979). Many bomber crews who survived raids deep into enemy territory tragically crashed their planes on reaching the safety of their home base because of a simple design flaw (Galotti, 2008).

Human Factors: Applied Psychology for Safety and Efficiency

The unfortunate saga of the B-17 triggered a radical revolution in aviation with a new awareness for the need not just to build great machines but to understand the humans who operate them. The team investigating the B-17 crashes came up with an ingenious idea known as shape coding: They recommended that crucial switches and controls on a flight deck should have unique shapes (often representing their function) so that pilots would intuitively feel when they reached for the wrong one. Shape coding has since become a legal requirement and is used on every commercially available airplane built since (Kuang, 2019).

Modern flight decks incorporate decades of psychological and human factor research to produce intuitive and state-of-the art designs.

Andrés Dallimonti | Unsplash

This revolution went even further and created the idea that machines should be designed around humans who operate them rather than simply trying to train people on whatever machine was built. This new approach birthed an entire new discipline within psychology and engineering called Human Factors and is at the heart of the ease of use of most things we use today.

From computers to smartphones, the user interfaces we now take for granted are the result of decades-long research and development that deeply examined how we perceive the world around us and how we act within it. Understanding human behaviour and cognition—the core tenets of psychology—is the essence of user-friendly design that resulted in tools such as the computer mouse and fire-door push-bars. Even when not directly related to safety, human factors play an important role in design that can have devastating consequences when ignored.

The Billion Dollar Mistake

In August 2020, Citibank distributed payments for a loan on behalf of a client but accidentally also sent all the lenders the principal capital on which the loan was based: over US$900 million (Stein, 2022). Later court filings showed that the mistake was made by a subcontractor who simply missed ticking two extra boxes on a very confusing and unfriendly user interface (Kay, 2021).

Interface used by Citibank at the time: A subcontractor missed ticking two boxes on the right, which resulted in a billion-dollar mistake

Court Filing

This example highlights how human factors play an important role not just in aviation and other safety-critical industries but across domains. Researchers have highlighted how user-centered design is imperative for technological development (Abras et al., 2004) and there is widespread evidence that applying human factor methods rooted in psychology to design has helped eliminate errors that can have significant negative consequences (Maxion & Reeder, 2005).

While some industries have been slow to pick up these principles, thankfully many safety-critical sectors have made them an integral part of their operations. Airlines have become incredibly safe, in part because of rigorously adapting human factor principles: 2023 was the second safest year on record with only 2 fatal accidents out of over 30 million flights—a ratio of one fatal accident for every 15 million flights (Calder, 2024).