Man and Machine — Page 283, Lesson 467

I want to walk you through the "Software" part of the Man and Machine chapter, starting with checklists and manuals. This is about the human factors side of the documents we use in the cockpit — not the aircraft's software, but the procedural software that guides our actions. Let's begin with the introduction. The importance of good design in checklists is fundamental to the safe operation of aircraft. That's a strong statement, and it's true. Aircrew must be afforded rapid accessibility to accurate information in manuals and checklists. In other words, you need to be able to find the right data fast, and it has to be correct. There is plainly a requirement for crews to be sufficiently familiar with their documentation so that they know where to find relevant information in the quickest possible time. So you can't just have the book on your knee — you have to know how to navigate it under pressure. Now, the main requirements for checklists. I'll go through each one. First, unambiguous. Every item must mean exactly one thing — no room for interpretation when you're busy. Second, easy to read. That sounds obvious, but it's a specific design goal. Third, kept to a manageable size for easy use on the flight deck. A checklist that's too big or too long becomes a hindrance, not a help. Fourth, fullest use is made of good cross-referenced indexing and colour coding of pages by topic. So if you're looking for the engine fire procedure, the index should point you there clearly, and the pages for that topic might be a consistent colour so you can flip to them quickly. Fifth, division of pages with protruding thumb locators. Those are the little tabs that stick out from the side of the page — they let you feel your way to the right section without having to look. Sixth, amount of information presented is relevant to the needs of the pilot. No extra clutter. Only what you actually need for that task. Seventh, presented in easily understood language. Plain, direct phrasing — no jargon that isn't explained, no ambiguous wording. Then we get into text specifics. Size should be kept well above the minimum required for bare legibility since it may have to be read in poor lighting conditions by a crew that already has a high workload. So don't just make it big enough to read in perfect light — make it bigger, because you might be in a dark cockpit with a lot on your mind. Type face should maximise legibility. That means a clean, clear font — nothing fancy or hard to decipher. A mix of upper and lower case together with bold and italics should be used with care to maximise clarity and emphasis. So you can use these tools, but you have to be deliberate about it. And here's a critical note: UPPER CASE text and the use of italics may be useful in conveying emphasis but neither of these are as fast to read as normal text. So if you write a whole sentence in capitals, it actually slows the reader down. The note drives this home: THUS LONG MESSAGES, IN UPPER CASE, SUCH AS THIS, SHOULD BE AVOIDED SINCE WORD SHAPE WHICH ACTS AS A CLUE IN READING, MAY BE LOST. That's the key point — when you read normal mixed-case text, your brain recognises the shape of the whole word, not just individual letters. All capitals destroys that shape cue, so reading becomes slower and more effortful. Now, use of colour. Colour is a preferable way of categorizing information and giving importance to different sections of text. So you might have emergency procedures in red, normal checklists in black, that kind of thing. But — and this is important — the legibility of different text/background may well vary under varying light conditions. For example red text on a white background may become effectively invisible under red light. And red light is common in cockpits at night to preserve night vision. So a colour scheme that works in daylight might completely disappear when you need it most. Finally, checklists — design usage. The maximum benefit is obtained from checklists when the pilot adheres to the designed procedure. If the checklist calls for a challenge and response, then this is the way it should be used. So if the procedure says the pilot flying calls out an item and the pilot monitoring responds, you do it that way — don't improvise. The design is intentional, and following it exactly gives you the safety benefit it was built to provide.