The evolution of cockpit design is credited to the advancement of Human Factors as a formal discipline. The definition of HF by Koonce (1979) reads “The study of the human’s capabilities, limitations, and behaviors and the integration of that knowledge into the systems we design for them with the goals of enhancing safety, performance, and the general well-being of the operators of the system”
Early Day Cockpits
The very early generation of flying was based solely on see (visual) and feel and was a relatively physical task. Control of the aircraft was solely ‘stick’ and ‘rudder’ and was a manual operation. Therefore Cockpit design was very basic with very few instruments to provide the pilot with information on aircraft and engine performance, cockpits normally consisted of three or four major instruments and there were only controls for basic flight.
Cockpit Layout (WW1 to 1980’s)
During the war, flying advanced in that aircraft were required to fly without visual cues, such as at night or in cloud, furthermore pilots were not only required to maneuver the aircraft but to navigate, fire weapons, deliver troops and perform other various duties. As the requirement for increased roles for the pilot were increased, so were the number of controls and instruments in the cockpit. As written by Salas and Maurino (2010) “More and more information placed inside the aircraft supplemented or replaced cues outside the aircraft”. This trend continued onto airliners up to the 1970’s until the number of instruments, knobs and controls outgrew the cockpit.
The increased number of flight and engine instruments resulted in the contrary to what designers had intended. There was limited integration of controls and instruments, and instead of increasing awareness to the pilot, workload and stress levels were increased. Wiener and Nagel (1988) summarized that “crew system designs and flight station layouts have frequently ignored the limitations and capabilities of the human operator”.
Human Factors influence on cockpit design and Layouts
The complexity in instruments displaying aircraft systems and performance resulted in high stress levels and error rates. Examples of this were missed signals, misinterpreted information and limited detection and recognition of a number of instruments by the flight crew (Weiner and Nagel, 1988).
Data shows that there was an increasing trend in the number of displays (Instruments & gauges) up until the 1980’s where there was a sharp decrease (Wiener & Nagel, 1988). The reduction of the number of instruments in cockpit designs coincided with the perception and human information processing focus that dominated the HF era in aviation around that same time (Salas and Maurino, 2010). It also coincided with the introduction of next generation aircraft such as the Boeing 757/767 and A310. In modern next generation cockpits the studies of these HF topics are reflected in design. There is not only a significant reduction in the number of instruments but the display of information in the form of glass cockpits reflects the improved understanding of the human cognitive process and the application to this in design of the systems (the objective of HF).
Design Considerations for the Modern day Cockpit
Anthropometry, which literally translates to ‘measure of man’, is the science of measuring human individuals (Aghazadeh, 1994).
Measurements can be in the form of
- Static measurements: Measurements when the body is still. (e.g. sitting height)
- Dynamic measurements: Measurements when the body is moving (e.g. a pilot’s reach envelope for the overhead panels)
- Contour measurements: Measurements of the body (e.g. head circumference or waist size)
Anthropometry in Aviation
Anthropometry is an integral part of ergonomic design, for aircraft designers anthropometry is not limited to the measurements alone but also who the targeted users and operators are. It is not feasible to design a cockpit for every individual in the world, rather a normal distribution is used where an aircraft is designed for the 5th to 95th percentile of the intended population (NASA, 1978). (note that this is not the same as the middle 90% of the population)
|Distribution of the 5th-95th percentile (image embedded from Webanswers on 12 August 2012)|
Anthropometry considerations in aviation include
|Body dimensions||Clothing (including gloves, shoes) of crew uniform|
|Hand size||Size, location and layout of button, switches, levers and small controls. Maintenance access for engineers|
|Length of arms and legs||Reach envelope for control locations|
|Sitting eye height||Seat adjustment to establish correct eye datum|
|Sitting height, sitting knee height and thigh thickness||Control column yoke clearance, desk and console design|
|Standing height||Ceiling and door height limitations, overhead panel reach|
|Sitting elbow rest height/ length||Armrest location|
|Body width and thickness||Fuselage, passageway, door and hatch size limitations|
|Thigh length||Seat length|
|Foot size||Foot location, space and controls (rudder and brakes)|
|Muscle strength||Control feedback forces (real or artificial). Service and maintenance requirements. Portable equipment weights|
Design eye position/ Eye Datum
The design eye position, also known as eye datum or design eye reference point (DERP) is one of the key aspects of cockpit design. A pilot should be able to view all the main cockpit instruments while maintaining a reasonable view of the outside world with minimal head movement (FAA, 1993). The instruments should be located high enough for easy viewing but low enough so that it does not obstruct the view of the runway ahead during take off and landing. The aircraft designer will first allocate a design eye position and from there build the cockpit around it, factoring in the reach envelope the designer can then position the controls, switches and dials to cater for the 5th to 95th percentile of pilots (Coombs, 1999).
In order to operate the aircraft as intended it can be seen that all pilots must use the same reference datum. This is normally achieved by adjusting the seating position in both vertical and fore/aft axis. Some aircraft will also have adjustable rudder pedals and/or control yoke/joy stick to ensure the pilot’s view is in alignment with the design eye position. To highlight the significance of the design eye position, sitting just 1 inch below the reference point on a Boeing 767 will result in losing 40 meters of ground vision during final approach.
Rarely does the cockpit design take precedence over the aircraft fuselage shape. A compromise therefore exists between the ergonomics and anthropometry of the cockpit and the aerodynamics and strength of the aircraft body. Nevertheless, the cockpit should be designed to be as spacious as possible. One way to achieve this is by de-cluttering the cockpit, position of a particular control will be based on the importance and frequency of use as well as whether the requirement exists between having it duplicated or shared (Enol, 2012). For example, the throttle levers, which are shared controls, are limited to be positioned somewhere in the middle of the cockpit so that it is accessible by both crew. Should a control be off-centred beyond the reach of one crew (such as the flap lever on some aircraft), then the pilot on the respective side will be solely in charge of manipulating that particular control. While this may create additional complications during unfavourable scenarios, due to workspace constraints it is not practical to duplicate all the controls and certainly not have all the controls in the middle of the cockpit.
Airline pilots remain seated for an extended period of time, long haul routes are often in excess of sixteen hours. While the importance of seat comfort itself is explanatory, there is also big emphasis on designing a seat that offers sufficient back support (Roskam, 2002). More information on aircraft seat ergonomics can be found here.
Humidity and illumination can also affect pilot comfort. Most large aircraft cockpits have a separate environmental control panel for pilots to regulate the ambient temperature. The difference in insolation due to the large windscreens often means that the cockpit will require a different setting than the rear cabin. The illumination on the left and right side of the instrument panel should have the ability to be adjusted independently to suit the individual pilot.
The main function of the safety harness is to reduce the momentum of the pilot (Jarrett, 2005). The harness secures the pilot during turbulence or in emergency situations such as rapid descend or explosive decompression (eg: windscreen failure). For this reason the safety harness must be wore at all times during flight.
There are four main types of safety harness:
|Lap||Single belt that is wrapped across the waist. This is not an acceptable form of cockpit safety harness as it provides little to no protection across the various planes of motion|
|Three point harness/ sash||Most commonly found in automobiles, although the three point harness provides good protection along the fore/aft plane. It does not provide adequate protection for lateral and vertical movements aircrafts are subject to|
|Four point harness||This is the ideal harness and almost universally used in all modern airliners|
|Five/six/seven point harness||Similar to the four point harness but with additional straps. This is used extensively in aerobatic aircraft but too cumbersome for airline use|
Most harnesses utilise an inertia reel which consist of a centrifugally operated internal mechanism that allows slow (intentional) movements but locks under quick travel. Most inertia wheels are designed to lock at 1 ‘g’ deceleration and can sustain a short burst of 20 ‘g’ deceleration without breaking (Coombs, 2005).
The display is the presentation of information and can come in the form of visual, aural or tactile. While visual is the main form of display in the cockpit, aural and tactile has its uses as well. Aural warnings from the likes of ground proximity warning system (GPWS) or traffic collision avoidance system (TCAS) and tactile warnings such as the stick shaker are powerful aids for the aircraft to communicate and alert the crew. Warnings will be discussed in more detail later.
As mentioned previously the display in the modern cockpit is designed around the design eye position. Ideally all displays should be large, legible, well lit and easy to operate. Due to workspace constraints however more prominent and frequent displays will have priority over ones that are less essential.
There are two forms of display design, analogue or digital.
|Analogue display||This type of display has the advantage that information represented by the needle can be interpreted almost instantly. The needle can provide information on direction and rate of change which can be interpreted with little effort required. Comparing information is also easier on an analogue display, a quick glance of two gauges with parallel needles in the green arc is a good indication that they are both operating within limits, there is no need to read into the quantifying numbers. This is why the analogue scale is still preferred in many instruments and is by no means limited only to traditional analogue instruments. Various perimeters on a glass cockpit display have adopted the analogue scale display. It should be noted that analogue display is not limited to circular or semi circular pointers but can also be vertical or horizontal (e.g. the vertical speed tape on a modern glass cockpit display is a form of analogue display).|
|Digital display||Digital display provides information by producing plain numbers. A calculator is the best example of a day to day digital display device. Digital display is useful when we are concerned about exact numerical values. Instruments that utilises digital display include the frequency selection panel, DME readout and altimeter subscale.|
The downside of the analogue display is that the ease of interpretation quickly diminishes with the introduction of the third needle. For example, a three point altimeters can take three times longer to interpret compared to a digital readout (Pallet, 1992). It can be seen that some instruments, such as a fuel gauge, will benefit greatly with a combined analogue and digital readout. A combined display will enables the pilot to read or compare (rough) figures quickly but if needed also determine the exact quantity of measurement.
Display light and colour
Illumination and colour plays a vital role in instrument displays. Instruments and controls can be lit internally, externally or both. Aircraft designers need to ensure lighting does not create glare or shadows and produce the correct brilliance for day and night operations. There should then be a way for pilots to fine tune the luminosity to accommodate each individual’s light sensitivity. Modern day LCD screens on glass cockpits have a narrower field of vision, however, as long as the pilot is seated aligned with the design eye position the display should not interfere with everyday operations (Nagabhushana & Sudha, 2011).
The correct use of colour schemes can aid in alerting the crew if something needs to be bought to attention. Using too many different colours however may clutter the screen and cause confusion. The main colours used for system monitoring are green (normal), amber (caution) and red (alert or emergency). On the horizontal situational indicator (HSI), the following colours are typically used.
|Green||Active or selected mode and/or dynamic conditions|
|White||Present status situation and scales|
|Magenta||Command information, pointers, symbols and fly to tracks. Magenta is also used on the weather radar to indicate areas of strong return (ie: possible turbulence/wind shear)|
|Cyan||Non active and background information|
|Yellow/Amber||Cautions, flags and faults|
|Black||Blank areas or system off|
Control layout and design
Aircraft controls supplement aircraft displays in communicating to the pilot. It provides a two way interaction between the aircraft and the crew. Controls should be easy to reach and be positioned appropriately in accordance to their usage. Controls which are used frequently should be positioned in a more prominent position. Controls should move in the natural sense and controls that complement each other or frequently used in conjunction of each other should be grouped together if possible (Jarrett, 2005).
Standardisation is important to avoid unnecessary confusion (Roskam, 2002). Although different aircraft manufacturers have their subtle differences, generally the layout of controls and gauges are set in the natural sense. Good aircraft type knowledge may not always prevent inadvertent actions. The Beech Bonanza, a popular light twin, initially had the gear lever positioned on the right side of the throttle quadrant, a position commonly used for flap settings. This resulted in numerous gear up landings where pilots raised the gear during short finals when the intention was to lower flaps. The manufacturer soon repositioned the gear lever as well as adding a squat switch to prevent the gear rising below a certain power setting. The accident records for gear up landings on the Bonanza is about 40% higher on the earlier non-standard cockpit layout aircraft than the later revised models (Landsberg, 1994). Other notable non-standard control layout aircraft include the Douglas DC-3, where the throttle quadrant levers are arranged as pitch, throttle then mixture as opposed to the standard throttle, pitch, mixture arrangement. Other layouts, such as the standard ’T’ instrument arrangement have remained the same since it was first derived.
Shapes and colours
Shapes and colours are also used in control levers and switches to reduce ambiguity and inadvertent operation. Below are some of the shapes, colours and order of controls recommended by the Federal Aviation Administration (FAA) for general aviation aircraft to adopt. This is also part of standardisation mentioned in the last paragraph.
|(From left to right) Black and Round - Throttle, Blue with three points - Pitch, Red with multiple points - Mixture, Silver and Jaggered edge - Supercharger|
The direction of controls and levers should operate in the natural sense and also flow with the checks and procedures. It is natural for example, to turn a dial clockwise to increase something and anticlockwise to decrease. In an emergency situation where the pilot is overloaded with information, switches and controls will be operated in an instinctive manner which may be opposite to what the pilot intends to do if it is not designed to operate in the normal sense. Boeing’s philosophy on switch direction is the ‘sweep on’ concept, where all switches on the cockpit sweep/switch on with the arm rising up no matter where the switch is located. Although this is very different compared to the Airbus single push ON/OFF button operation, the commonality between the two design philosophies is that it is put in place to reduce the chance of inadvertent operation. The Diamond DA42, a modern light twin training aircraft, has three identical levers for the park brake, cabin heat and cabin defroster situated together forward of the main throttle quadrant. The aft position of lever is to turn the cabin heat and cabin defroster unit OFF but park brakes ON. There has been cases where aircraft have landed with park brakes on (in some cases resulting to a forward flip), the natural tendency for the pilot to line up all the levers would have contributed to the cause of the accidents.
Control loading is the amount of forced feedback the pilot receives when manipulating the primary flight control. The force feedback must not be too strong that an average strength pilot will have difficulty in moving the controls, nor too light which will create over controlling problems. The force should be linear and equal between different axis (ie: the sensitivity of pitch and roll are not vastly different). The force should be strong but sensitive enough for the pilot to appreciate what is happening and provide control responses matching to what is required (Enol, 2012). On large aircraft with hydraulic systems this can be achieved by manipulating the control feedback motor torque, on aircraft with direct linkage between control and control surfaces, this is achieved by the use of aerodynamic devices such as trim tabs, anti trim tabs and horn balance which manipulate the aerodynamic force exerted on the control surface.
Aircraft warnings and alerts serve one of the four following functions
- Alert the crew of a problem
- Describe the nature of the problem
- Direct the appropriate actions
- Provide feedback (is the problem fixed or does it still exist)
Failures will either be a warning (red) or a caution (amber). A warning indicates that immediate crew action is required or there will be direct consequences to flight safety. A caution is to alert the crew of a failure although no immediate action is required (Nagabhushana & Sudha, 2011). Warnings can be presented in the form of visual, aural or tactile. While warnings should draw the attention of the crew immediately, it should not be done in such a way that it will startle the crew or append extra stress or workload.
Modern aircraft systems are integrals of many separate systems which may again be part of another subsystem (Pallett, 1992). Although any part of the system has the potential to fail, the workspace constraints makes it impractical to situate all the different warnings in prominent view to the pilot. Typically, a master warning and a master caution light is positioned somewhere directly in front of the pilot. Should the master warning or master caution light up, the pilot will have to determine the source of the problem by referring to annunciator panel located elsewhere or on a more modern aircraft opening the relevant pages in the EFIS system.
The most important aspect of any warning system is that it needs to be reliable and only report genuine problems or malfunctions. The crew must be able to trust the information presented to them, even in situations where it may appear to be contradictory to what is perceived to be happening. False warnings can be detrimental to flight safety, a false engine fire warning may result to an unnecessary in flight engine shut down, creating additional workload in an one engine inoperative environment. This is why with some systems such as the GPWS, it is mandatory by law to report any false alerts (known as nuisance warnings). The idea of compiling this information is to enhance the reliability of such a crucial equipment (Spitzer, 2006).
In the modern airline environment, the checklists is as essential as the instruments and controls themselves (Harris, 2004). Checklists and the cockpit layout should be coherent of each other and aircraft manufacturer would have had this in mind before arranging the cockpit layout. The actions should follow a practical flow pattern that is not only easy to remember but can also be conducted swiftly if required. More on checklists can be found here.
Glass cockpit and Automation
The vast information regarding the glass cockpit and automation warrant them to be covered as separate topics by themselves. Please click on the following links for further readings on the glass cockpit and automation.
Cockpit design and layout started from very basic which advanced to an overcrowded cockpit. The introduction of many instruments and gauges was for the purpose of providing information to the pilot regarding the performance of his/her aircraft. This however also resulted in high stress levels and a high error rate due to the lack of the human capability to process all this information. HF advanced in studies relating to the human cognitive process and attention and memory limitations in the 1980’s. As a result of the research carried out, cockpits were designed to better suit the human operator. Reduced number of instruments, the use of the Glass Cockpit and the display of information on these screens amongst many other things have all been introduced over recent years. It is inevitable that cockpit layout and design will change, but it is important that this change be in line with HF research which best suits the human operator and their limitations and capabilities.
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