Man and Machine — Page 283, Lesson 462

I want to walk you through two important areas in the cockpit environment: cockpit lighting and the basic design principles for controls. These are fundamental to how we, as pilots, interact with the aircraft safely and efficiently. Let's start with cockpit lighting. Every instrument needs a lighting system so you can read it in any light condition, from bright daylight to total darkness. On conventional dial instruments — the older round 'steam gauge' type — there are two main options: internal lighting built into each individual instrument, or external lights that illuminate a whole group of instruments. In most cockpits, you'll actually find a mixture of both internal and external lights. Now, in a glass cockpit — that's the modern electronic display setup — the brilliance control acts as an adjusting mechanism to cater for varying light conditions. Once you set it, the screen brilliance may be automatically retained by an ambient light sensor fitted in the cockpit. That sensor measures the surrounding light level and adjusts the display brightness to keep it consistent for you. What's essential in any system is an adjustment that allows for both the state of natural light outside and your own individual preference. All lighting systems should avoid harsh shadows and reflected glare, because those can hide information or cause eye strain. There's been a tendency in modern civil flying to use higher brightness levels on the flight deck. Research has indicated that on long night flights, fatigue and drowsiness seem to be less with higher brightness levels. This is especially relevant because with age, visual acuity — the sharpness of your vision — decreases, and older pilots require a higher brightness level to see clearly. There's also a specific operational point: should there be a possibility of thunderstorms or lightning, you should turn cockpit lights fully up. The reason is to reduce, as far as possible, the 'blinding' effect of flashes. If your cockpit is dim and a lightning flash occurs, your eyes will be much more severely dazzled. Turning the lights up high helps your eyes stay adapted to a brighter environment, so the flash has less impact. Now let's move to Hardware – Controls. This is about how we, as pilots, send instructions back to the aircraft. The basic idea is simple: displays pass information from the aircraft to the pilot, and controls pass instructions from the pilot to the aircraft. But there are several basic considerations that govern how controls should be designed and arranged. First, standardization. Most importantly, controls should be standardized in their location and sense of use from one aircraft to another, and between different aircraft types. For example, to operate a manual valve, rotation should be clockwise to close and anti-clockwise to open. That consistency means you don't have to relearn basic movements every time you step into a different aircraft. Second, frequency of use. Controls should be located within an easy reach envelope of all designed users of the aircraft. Controls that you use frequently or for protracted periods should be located so that they do not require an awkward or fatiguing posture. If you have to stretch or hold an uncomfortable position every time you adjust a frequently used control, that leads to fatigue and distraction. Third, sequence of use. Controls that are frequently used in a given order should be laid out so that the sequence of use is represented in the layout of the controls. As well as being convenient, the layout itself acts as a prompt for the pilot — your hand naturally moves through the correct order because the controls are arranged that way. Fourth, importance. Important controls must be located in easily reached and unobstructed positions. You don't want to have to move a chart or reach past something to get to a critical control in an emergency. Fifth, visual/tactile dissimilarity. Switches and knobs that control different functions should not look or feel the same. This reduces the chances of inadvertent operation — you can tell by touch or by sight which switch is which, even without looking directly at it. These principles might seem like common sense, but they are the result of decades of experience and accident investigation. They are built into the certification standards for aircraft design.