Textbook of Usability

Also known as: ergonomics, HFE

Human factors engineering (also called ergonomics, especially outside the US) is the discipline of applying knowledge about human capabilities and limitations to the design of systems, equipment, and procedures. It emerged during World War II when engineers recognised that many aircraft accidents were caused not by mechanical failure or pilot incompetence but by poor cockpit design.

The landmark case: Alphonse Chapanis, one of the founders of the discipline, investigated a series of gear-up landings in the US Army Air Forces. He found that pilots were retracting the landing gear instead of the flaps because the two controls were identical toggle switches located side by side. His solution — shape-coding the controls (a wheel-shaped knob for gear, a flap-shaped knob for flaps) — eliminated the confusion.

The key insight: well-trained, motivated professionals make predictable errors when design conflicts with human capabilities. The solution is better design, not more training.

Human factors engineering covers:

• Anthropometry (body measurements and reach envelopes)
• Physiology (fatigue, workload, circadian rhythms)
• Perception and cognition (vision, attention, memory limits)
• Motor control (Fitts's Law, reaction time)
• Decision-making (heuristics, biases, training effects)
• Team and organisational factors (CRM, shared mental models)

The discipline has shaped aviation, healthcare, nuclear power, and consumer product design. Its principles — error tolerance, standardisation, defence in depth — are the intellectual ancestors of much of modern usability and safety engineering.