ICAO addressed the topic of ergonomics (namely on the flight deck) in the 1992 circular Human Factors Digest no 61. Although the publication itself is relatively old, the ideas it describes are generic enough to remain valid today. The circular, however, is now more suited as a brief introduction to ergonomics than as a guideline for better design, and, as such, should not be used for the latter purpose. What follows is a synopsis of the contents in that circular, focusing more on its introductory value than on its practical one.
12. Today's approach to flight deck design strives to provide equipment which is "user-friendly" and "error-tolerant". These two concepts are synonymous with ergonomics as the user's characteristics (such as capabilities, and limitations) are taken into consideration from early stages of design.
Chapter 1. Basic facts about ergonomics
1.2. Ergonomics normally refers to "the study of human-machine system design issues"1. It is a term often used interchangeably with Human Factors2 although the later conveys a wider meaning, which includes variables outside the human-machine interface3.
1.10. From a systems' perspective, "Ergonomics will try to optimize the interaction between people and machines in the system, while taking into consideration the characteristics of all system components (ICAO, 1992, ch.1, p.6)".
1.11. Thus, the machine is a system component with displays and controls. The displays provide information to the human operator about how the system is doing. The controls allow this human operator to transfer orders to the machine. Equally, the operator is another system component. It perceives the information provided by the displays, and acts on the controls in order to manage the performance of the system. The boundary between the machine and the human is the "realm" of ergonomics, as it strives to create an effective human-machine interface. The better the fit between human and machines, the more reliable and predictable the performance of the system. Notice here that this interface works both ways: the machine's displays and controls should be compatible with human capabilities and limitations, but also the human can be matched to the machine configuration (e.g. through selection and training) when design has not yet matched those human characteristics.
1.12. Systems goals and operational constraints are also important conditions to take into account when designing human-machine interfaces. And those should be known by the ergonomist even before the design of the system starts.
1.13. Another important task for the ergonomist is deciding on the allocation of functions and tasks to either the human or the machine. Both should complement each other for best performance, but also be flexible enough to allow for different "configurations" of task allocation under different operational constrains (e.g. routine flight or emergencies).
1.16. The important role that ergonomics has to play in aviation safety is that of minimizing human error induced by poorly designed equipment or by stressful working environments. Of course, ergonomics can also enhance aviation safety by maximizing human performance under normal and abnormal conditions.
1.18. There are two ways of managing human error from an ergonomics perspective. The first is to minimize the occurrence of errors. This can be achieved by enhancing the human-machine interface (optimal machine design, and good staff selection and training), as well as the flight deck environment, and related tools (e.g. proper documentation). The second approach is to minimize the impact of errors once committed. This can be achieved by design (e.g. error-tolerant systems), as well as by safeguards such as cross-monitoring and crew cooperation.
Chapter 2. Human capabilities
2.1. The visual system is the predominant sensory system for humans, and the most important in their interaction with the environment. The visual system comprises not only the eyes (which sense colour, shape, movement, etc) but also the brain areas that process those sensations into coherent information (perception), the neurons that brings the signals to the brain as well as to the motor system that controls the movement of the eyes in their sockets as well as the pupil. Of interest to the ergonomist, however, are conditions surrounding the visual system at work, such as:
- 2.2. Light adaptation.
- 2.3. Visual acuity.
- 2.4. Focus.
- 2.5. Spatial orientation.
- 2.6. Perceptual ambiguity and uncertainty.
- 2.7. Psychological fascination.
- 2.8. Visual illusions.
2.9. The vocal system produces speech (sound waves) thanks to the lungs (which push air into the larynx), the glottis (which vibrates to produce the different vowels), and the larynx, mouth, nose and tongue (which help produce the consonants). Speech can vary in pitch and frequency, while also be affected by accent, etc. However, as long as the basic pattern of frequency is maintained, speech will remain intelligible. The auditory system, on the other hand, comprises the ears, auditory canals, middle ear bones, the cochlea and the organ of Corti (among other structures4). Hearing is achieved when sound waves in the air are transformed into fluid waves (in the cochlea) and these into nerve signals (in the organ of Corti), to be sent and processed by the brain. Of interest to the ergonomist, however, are conditions associated with sound transmission and perception such as:
- 2.10. Impaired hearing.
- 2.11. Sound properties (intensity, frequency, harmonic composition, and latency).
- 2.12. Noise.
- 2.13. Redundancy.
2.15. The brain is the ultimate human information processing system. Namely all data sensed by the sensory organs is sent to the brain for processing.
2.16. The brain perceives this data, transforms it into information, and makes decisions upon it. Once a decision has been made, the brain also commands the muscles to exercise the appropriate response. Because information processing and decision-making happen in a centralized organ also dedicated to many other cognitive processes, many variables influence or interfere with perception and decision-making. Expectations, experience, attitudes, motivation, arousal, conflict of interests, medication, psychological conditions, etc play a role in how we perceive and act at any one time. Of interest to the ergonomist, however, are conditions that influence human information processing, such as:
- 2.17-2.20. Memory span and limitations.
- 2.21. Attention span.
- 2.22. Mental workload.
2.23. Matching the working environment and working tools to human dimensions, their natural range of movement and strength is of primary concern for ergonomics. Ergonomics draw knowledge from disciplines such as anthropometry (which studies human dimensions such as weight, stature, limb size, etc) and biomechanics (which studies the movement of body parts and their forces) to help design better work environments. Of further interest to the ergonomist are also other related conditions, such as:
- 2.24. Physical changes across generations.
- 2.25. Differences among ethnic groups.
Chapter 3. Displays, controls and design
3.3. The function of displays is to present information to the operator. This information should be timely, appropriate, accurate, and adequate, relevant to task requirements and take human capabilities into account. Of interest to the ergonomist are display conditions that may either enhance or be detrimental to human performance, such as:
- 3.6. Design and location of displays.
- 3.7. Display of alphanumeric data.
- 3.8. Dial markings and shapes.
- 3.9. Electronic displays.
- 3.10. Heads-up displays (HUDs).
- 3.11. Advisory, caution and warning systems.
3.14. The function of controls is to allow the operator to command the machine. Controls should allow commands to be transmitted accurately and timely, but should also take human capabilities into account and be tolerant to human error. Of interest to the ergonomist are control-related conditions that may either enhance or be detrimental to human performance, such as:
- 3.16. Functional requirements and manipulation forces.
- 3.17. Location of controls.
- 3.18. Control-display input ratio and movement ratio, control movement, control coding, and protection against inadvertent operation.
- 3.19. Keyboard design and layout.
3.20-3.33. Finally, ergonomics is of importance to flight deck design. It draws knowledge from systems engineering in order to integrate the whole array of displays and controls within the range of movements and tasks of the pilots at work.
Chapter 4. The environment
The flight deck environment also plays a role in human performance. Of interest to the ergonomist are variables within this environment that may either enhance or be detrimental to human performance, such as:
- 4.4-4.8. Noise
- 4.9-4.12. Temperature
- 4.13. Humidity
- 4.14-4.15. Pressurization
- 4.16-4.17. Illumination
- 4.18-4.20. Vibration
Want to know more?
- AviationKnowledge - ICAO Human Factors
- This AviationKnowledge page provides a synopsis of ICAO's Digest number 1, an introduction to Human Factors.
- ICAO's Human factors digest no 6
- As indicated earlier, this digest is more an introduction to ergonomics than a guideline for ergonomics in the flight deck. Therefore, its usability is limited. You can purchase it from ICAO, as "ICAO - INTERNATIONAL CIVIL AVIATION ORGANIZATION (1992). Human factors digest no 6. Ergonomics. Circular 238-AN/143. ICAO (Montreal, Canada), 1992."
Jose D PEREZGONZALEZ (2009). School of Aviation, Massey University, New Zealand (JDPerezgonzalez).