Man and Machine — Page 283, Lesson 464

I want to walk you through some key design principles that govern how pilots interact with aircraft controls and warnings. These are part of the broader topic of Man and Machine — the human factors side of cockpit design. Let's start with symbolism. The idea here is that controls should, where possible, be shaped or marked in a way that hints at their function. For example, an undercarriage lever can be shaped like a wheel, and a flap lever can be shaped like a cross-section of a flap. This helps you identify the control by touch alone, without having to look down. Next is control/display compatibility. This means the physical location of a control should maintain a logical spatial relationship with the display it operates. A classic example: the columns of engine instruments — like the gauges showing RPM, temperature, and pressure for each engine — should be aligned directly with the corresponding power levers. So if you have two engines, the left engine's instruments sit in a column above or beside the left power lever, and the right engine's instruments align with the right power lever. That way, your hand and your eye are working in the same spatial frame. You can see examples of this in and . Now, control loading. This refers to the force required to move a control. That force must not only be within the physical capability of the target pilot population — meaning the range of pilots who will fly the aircraft — but it should also be harmonized with the forces required by other related controls. For instance, if a control column needs a large force to roll the aircraft but only a light force to pitch it, that mismatch makes the control difficult and uncomfortable to use. The forces should feel balanced and consistent. Then we have prevention of inadvertent use. Controls should be designed to minimize the chance you'll operate them by accident. Where accidental operation could be dangerous, the control should be fitted with a guard — a physical cover or latch you have to deliberately move before you can operate the switch or lever. Next is control position and present demand. The physical position of the control should tell you what function is currently selected. In some modern cockpits, the conventional control column has been replaced by a sidestick — a small joystick mounted on the side console. If both pilots have sidesticks, those sidesticks should move in unison. That way, when you take control from the other pilot, you can feel where the stick is already positioned, so you know the current demand being sent to the flight controls. Finally, simultaneous use. Controls that need to be operated at the same time — like the throttle and the trim controls during a go-around or a power change — should be located so that you can reach and operate both at once without awkward stretching or releasing one to grab the other. The text notes that great progress is being made to meet all these requirements, but even today some aircraft designs still have problems. Some are just a nuisance, but others should not be tolerated. Examples of those problems appear in Chapter 16, in reports submitted by pilots. Now let's move to warnings. This is a critical area. Every warning system must be 'attention getting' without being startling. It should not scare you, but it must grab your attention. Beyond just attracting attention, the warning should inform you of what is wrong and, if possible, guide you to the correct actions. For all important failures, the alerting function should be fulfilled by an audio warning. This is mandatory if the pilot is required to assume control — meaning if the failure demands that you take over manually, you must get an audible alert. Why? Because even the most conspicuous visual warnings rely on you looking in the right direction — they depend on head and gaze orientation. In a more extreme example, any visual warning is useless if the pilots are asleep. So the ideal warning system is this: a single audio warning that alerts you to a failure, and that audio directs your attention to a single central warning panel. That panel then announces the nature of the problem with a suitable illuminated caption — a light that tells you exactly what has failed. It is vital that warning systems be reliable. That means they respond to all genuine problems, but they do not generate false alarms. Early GPWS systems — Ground Proximity Warning Systems — were well known for generating spurious warnings, false alarms that went off when there was no real danger. It has been suggested that CFIT accidents — Controlled Flight Into Terrain, where a perfectly flyable aircraft is flown into the ground — have been caused by pilots who were so used to hearing spurious warnings that they ignored a genuine alarm. So reliability is not just a convenience; it is a safety-critical requirement.