First, let me define what we mean by an action slip — Page 160, Lesson 257

I want to walk you through two specific types of errors that can happen when we rely on motor programmes — those well-practiced, automatic sequences of actions we develop through skill learning. First, let me define what we mean by an action slip. An action slip occurs at the selection stage of a motor programme. That means you've correctly learned the drill for one situation, but you accidentally select and execute the wrong programme for the situation you're actually in. For example, imagine you have an engine failure drill memorised perfectly. If you experience a loss of hydraulic pressure, you might find yourself running the engine failure drill instead — because that's the programme your brain selected, even though it's the wrong one for the event. A very common real-world example is reaching for the flap lever when you actually meant to lower the landing gear. Another example: a student knows the correct answer to a multiple-choice question but marks the wrong option on the answer sheet — that's an action slip at the selection stage, not a knowledge failure. The second error is environmental capture, also called habituation. This happens when an action is performed so frequently in the same environment that the environment itself triggers the motor programme automatically, even when the action isn't appropriate. The classic aviation example: a pilot on final approach confirms "three greens" — meaning three green lights indicating the landing gear is down and locked — without ever actually selecting the landing gear down. This happens when a pilot has practised many circuits, and the familiar environment of the final approach triggers the verbal confirmation habit. When questioned afterward, those pilots are genuinely convinced they saw three green lights, even though the landing gear was never selected down. The environment captured their behaviour. Now, the excerpt makes an important point: these two errors — action slip and environmental capture — are the major disadvantages of motor programmes. The only way to avoid them is for pilots to constantly monitor both their own motor actions and each other's. You must carry out drills and checks diligently, and never automatically. That last word is critical: never automatically. The moment you let a check become purely automatic, you open the door to these errors. Finally, a note on terminology: action slip and environmental capture are sometimes grouped together and called routine errors. A routine error is any error immediately associated with a motor programme — that is, any mistake that comes from executing a well-practised skill rather than from a lack of knowledge or ability.