Anthropometrical considerations

When designing a cockpit the manufacturer needs to ensure that the pilot can be seated comfortably, can reach all the required controls and can fit through the normal and emergency entry and exit routes. This presents a considerable challenge to the designer because of the extreme variability of the human body. None of us are identical (some twins excepted!) and even when individuals are of the same height they may have very different measurements for body parts such as thigh length, functional reach, etc. A considerable amount of research has been conducted into the anthropometrical measurements of pilots. For example, surveys have been conducted of RAF aircrew [7.3 and 7.4] and these have been used as the basis for the design requirements of UK military aircraft [7.1 and 7.5]. It is worth noting that there is also considerable variation between different groups in a population, and between the populations of different countries so that cockpits designed to suit the mean of one ethnic group may not be ideal for another.

The designer could use the average measurements of the intended pilot population for each body part in his calculations. This would be better than designing for one or other extreme of size but would still mean that pilots larger or smaller than the average (in effect just about everyone!) would have difficulty in fitting into the cockpit or reaching the controls. To overcome this problem the designer usually provides a range of movement for the seat and yaw pedals. On some occasions an extreme percentile determines the design, for example the door opening must allow the largest pilots to fit through. The range of sizes that the designer must cater for has increased in recent years as more women, who are generally smaller, have entered the previously exclusive domain of male pilots.

7.2.3 Controls

The helicopter cockpit incorporates a plethora of switches and controls, each of which must be designed carefully to assist the pilot when operating the aircraft. Switches must be easy to locate, identify and operate under all conditions. There are a number of means at the disposal of the manufacturer to achieve these design aims. Switches can be grouped together by function, such as locating all electrical controls on a single panel. Alternatively they may be grouped according to task, such as having all the controls required for engine start located together and arranged in the order in which they will be used. The frequency with which a control is used is also a factor in deciding its location, so that frequently used items are located where they can be operated by the pilot most easily. Less commonly used items can then be located in the less convenient positions, however, some infrequently used controls are of great importance and must therefore be particularly easy to locate. Controls associated with emergency actions are the prime examples of this. For example, fuel cut-off levers and engine fire extinguisher buttons may be used only very rarely but must be as easy as possible to locate, identify and operate in the case of an emergency.

Identifying the function of a switch or control and identifying the purpose of its selection positions are important aspects of design and assessment. The pilot must be able to identify a control quickly and accurately even when he or she is tired, busy or frightened. Furthermore the effect of selecting each position on the switch or control must be immediately apparent. To achieve these aims, switches and controls have to have correct labelling which can be read under all circumstances. For example, if the aircraft is to be operated at night the labels must have adequate illumination. It is also often necessary to provide more feedback about the status of a selected system than merely the position of a switch. This can take the form of lights or indicators to show that the system has been selected and is operating. The marking of controls associated with emergency actions such as door jettison handles and an underslung load jettison switch is an area where clear marking is essential. For this reason all specification documents that cover cockpit layout lay down in some detail the size, colours and position of markings for these controls.

The designer must give the pilot control over all the aircraft systems which means that he or she can close down engines, discharge fire extinguishers, disengage flight computers and jettison parts of the aircraft or its cargo. Clearly a lot of design effort must be made to ensure that these events only happen intentionally. Aviation history is littered with examples of aircrews who have made inadvertent or incorrect switch operations, often with disastrous results. There are a number of steps that can be taken to minimize the chances of this happening. Where inadvertent operation is likely to have a serious consequence controls may be provided with gates or guards which require a conscious action to release or pass and operate the control. Electrical interlinks to disable a switch if the system configuration is not correct can also be employed, such as weight-on-wheels switches to disable undercarriage selectors when the aircraft is on the ground. Other methods of minimizing inadvertent operation include covers, catches, recessing, wire locking or any combination of these.

Designers can also ensure that it is easy to discriminate between switches by using different shapes, colours, sizes and even textures. A cockpit full of identical switches may look good in the manufacturer’s brochure but it will spell disaster for the operational pilot. A good example of the use of shapes is the Westland Sea King autotransition panel, which employs a triangle, a cross and a bar to allow discrimina­tion between three controls at night.

The distance between controls and their method of operation are also important factors that must be considered. For example, locating a heater control next to a fuel jettison lever would clearly not be sensible particularly if both controls operated in the same sense.

A well designed system will give immediate feedback of the system status independent of switch position. For example, if a fuel boost pump is selected on, an indicator could change from red to show a white line completing that part of the fuel system schematic. On a less sophisticated system the pilot has to use the selection position of the switch itself to gain information about the system status. This can add significantly to the pilot’s workload and can also lead to errors, particularly for switches with multiple selections and those located further away from the pilot. Illumination of remote or integral lights and the use of indicators are the most common way of achieving status feedback.