Chapanis found that the controls for the [World War II Flying Fortress] Wing Flaps and Landing Gear looked exactly the same AND were positioned close to each other.

So close to each other in fact, that exhausted pilots approached the runway and flipped the switch for what they believed to be the landing gear, but instead flipped the wing flaps switch, slowing their descent and then grounding the plane.

Today, not only are the two controls fairly far apart in the cockpit, the lever for the Flaps is large and squared, while the Landing Gear’s knob is shaped like a wheel — as recommended by Chapanis.

More context and photos here: https://medium.com/swlh/the-flying-fortress-fatal-flaw-694523359eb

https://en.wikipedia.org/wiki/Shape_coding