Man and Machine — Page 278, Lesson 451

I want to walk you through the interface between the pilot and the aircraft — what we call the Man and Machine relationship. We've already looked at how the aircraft environment is adapted to human needs through pressurisation, soundproofing, and air conditioning, which controls temperature and humidity. That's the Liveware–Environment interface. Now we turn to the two remaining interfaces: Hardware and Software. Let's start with Hardware, specifically the design of flight decks. A fundamental feature of cockpit design is that the pilot must be able to see all important displays inside the aircraft and maintain an adequate view of the outside world without making more than the minimum of head movements. That means the cockpit space has to be designed around a defined position of the pilot's eye. This position is called the Eye Datum, also known as the Design Eye Position or Reference Eye Point. In the cockpit, it's often indicated by a marker on the central windscreen pillar — a little indicator that only appears aligned when your eye is exactly at the designed point. Why does this matter? Because the external view is particularly important. You must, without strain, be able to look over the top of the instrument panel and see enough of the ground ahead to land the aircraft. If you're sitting below the eye datum, the undershoot area — the ground just before the runway threshold — will be obscured. If you're sitting higher than the datum, the overshoot area — beyond the runway — may not be visible. And in that latter case, the aircraft instruments may also be difficult to read accurately. Once the design eye position is set, and once the anthropometric range of pilots — that is, the range of human body sizes and shapes — has been determined, then the size of the cockpit workspace and the amount of adjustment needed for the seat, rudder pedals, and so on can be established. But the designers are constrained by a key fact: the cockpit, for aerodynamic reasons, is placed in the narrowest section of the aircraft. Now let's move to Aircraft Windows. External vision is of great importance, but the size and shape of windows are determined by aerodynamic and weight restrictions. Large windows need thicker glass and require stronger, thicker frames. So a compromise must be reached: you get reasonable external vision without too great a weight penalty. Next, the Design of Cockpit Seats. Each year, flight durations continue to increase. Pilots spend longer and longer in the seat, so it's of the utmost importance that the seating is comfortable and adjustable to each individual pilot's size and shape. Flight deck seating must have a lumbar support to maintain the natural shape of the spine. That reduces the chances of lower back pain caused by a failure of the shock-absorbing discs between the vertebrae. Additionally, the seat should, if possible, be isolated from vibration of the airframe. Finally, restraint. You need a 5-point harness with a negative g strap. The negative g strap holds the harness in position during negative g manoeuvres — that is, when you're being pushed upward out of the seat — and it prevents 'submarining' under the lap strap during rapid deceleration. Submarining is exactly what it sounds like: sliding forward and down under the lap belt, which can cause serious injury. So to summarise: the cockpit is built around your eye datum, windows are a compromise between vision and weight, seats must support your spine and isolate vibration, and the harness must keep you firmly in place through all manoeuvres. That's the hardware side of the Man and Machine interface.