DVI Aviation has Aviation Human Factors Experts that specialize in aircraft cockpit design and the coding or identification of aircraft controls. The cockpit figures prominently in any safety analysis because it is the one aircraft area that must meet the requirements of flight and concurrently provide for the requirements of the human occupants. DVI’s Aircraft Cockpit Design Experts understand how the design or placement of cockpit controls can cause possible pilot confusion and contribute to an accident.
While operating an aircraft it is highly desirable that the pilot be able to locate quickly and identify accurately the various controls. The importance of correctly identifying controls was first studied by the USAF in a survey of pilot errors. Five hundred pilots were asked to describe an error that they had made or had seen someone make in using controls. Of all the errors reported, 50% involved the operation of a wrong control. To alleviate this situation, certain critical cockpit controls can be functionally coded to aid the pilot in efficient and correct identification. Some common coding techniques include differentiating: (1) shape, (2) size, (3) position or location, (4) color, (5) mode of operation, and (6) labeling.
Control Shape. Shape can be used to provide a pilot with tactile cues indicating a control's purpose. For example, a switch for the aircraft’s flaps could be shaped like an airfoil or wing, while the landing gear retraction switch might be rounded to represent a miniature wheel. The US Air Force has developed 15 knob designs that are not often confused.
Control Size: Another way that the controls might be made distinguishable is by using different sizes. A disadvantage of coding this way, when considered alone, is that the number of tactually discriminable steps that may be used in the operational situation is quite small. A distinction should be made between two kinds of size discriminability. One is "relative" size discriminability; the other, "absolute." By "relative" size discriminability is meant the ability to tell the difference between two different sizes by comparing one with the other. "Absolute," on the other hand, means that no such comparison is made. The operator simply remembers that a knob is of a particular size.
Location: In order to ensure discriminable and unique control locations, controls must be separated by distances that are sufficient to avoid confusion among positions.
Colors: The use of red, orange, yellow, green and blue are easily recognized. Examples of color coding includes: cockpit warning lights are usually red or amber. Green lights are used in the cockpit to indicate the position of the landing gear. On some instruments, the appearance of a red flag indicates that the instrument is not operating properly. The green area on the face of some instruments indicates their operating range, whereas the red area indicates a dangerous operating condition. It should be noted that under low levels of illumination, color is greatly modified and at times lost. Red may become a dark gray, and blue, a light gray. Under red lights, colors lose their identity and appear grayish, possibly tinged with red or green. For example, light blue, under red light, may appear black, while yellow might appear reddish white, etc. In general, the greater the variation in the ambient illumination, the less the value of color coding.
Mode of Operation: Another method of making controls distinguishable is by varying the way in which the controls operate. For example, if two controls identical with respect to color, size, shape, and, even, position. However, if one of the controls is a push-pull type and the other a rotary control, they will tend to be distinguishable by the Pilot. This can also include control resistance, which can affect the speed and precision of the operation, the “feel” of the control, smoothness of control movement, and the susceptibility of the control to inadvertent operation.
Labeling: Labeling should be accurately perceived under the operating conditions.
Another key consideration in cockpit design and control placement is the placement of the pilot in the aircraft. DVI has Aviation Biomechanical Experts that can evaluate pilot seating and reach positions. For example, In December of 1981, a Piper Comanche aircraft temporarily lost directional control in gusty conditions within the performance specifications of the aircraft. The pilot later reported that with the control column full aft, he was unable to maintain adequate aileron control because his knees were interfering with proper control movement (NTSB database). When designing a cockpit, engineers should determine the physical dimensions of the operator. There are three basic design philosophies that should be adhered to when designing around physical dimensions: (1) reach and clearance envelopes, (2) user position with respect to the display area, and (3) the position of the body.