Human factors issues, specifically human errors, contribute to more aircraft incidents and accidents than any other single factor. Human errors include errors by the flight crew, maintenance personnel, air traffic controllers, and others who have a direct impact on flight safety.
What lies behind human error is very frequently inaccurate situational awareness: the failure (for whatever reason) to evaluate an operational or maintenance situation properly. Thus, whenever the term human error appears, the reader should keep in mind that situational awareness, or the lack thereof, is usually the dominant factor. This can be a critical problem. As noted in Chapter 2, lack of situational awareness is a key factor in CFIT (controlled flight into terrain) accidents, which are responsible for more fatalities than any other type of aircraft accident.
This chapter discusses the relationships between human factors, environmental factors, and equipment factors in accidents and incidents; reviews current initiatives to reduce accidents and incidents associated with human errors or misunderstanding; and recommends steps the FAA can take to improve the effectiveness of its human factors work.
RELATIONSHIPS BETWEEN HUMAN FACTORS, ENVIRONMENTAL FACTORS, AND EQUIPMENT FACTORS IN ACCIDENTS AND INCIDENTS
Human factors are significant contributors in approximately 70 percent of all accidents and incidents. In a review of several databases, the committee found values in the range of 60 percent to 85 percent. These differences do not reflect on the integrity of the databases; they reflect the databases' different purposes and the understandable difficulties that arise from the substantial overlap of environmental, equipment, and human factors issues. This overlap, which is illustrated in Figure 5-1, is intrinsic to a complex system with a large number of possible accident and incident sources (primary and contributory). For example, adverse weather (or the threat of adverse weather) can contribute to an accident in many different ways. Weather information is generally, but not always, accurate; weather information provided to flight crews at dispatch and in flight is generally, but not always, timely; flight crew decisions based on available information are generally, but not always, made in accordance with prescribed procedures. There is no clear way, and indeed no practical need, to separate entirely environmental from operational factors.
Inaccurate situational awareness by the flight crew can arise in several different ways. Some examples are listed below:
The flight crew may not have critical data necessary to adequately define its situation, which may lead to inappropriate decisions and, ultimately, an accident.
The flight crew may have the data it needs but misinterpret the data.
The flight crew may have the data it needs, properly interpret the data, and accurately define the situation, but it may not have the training, skills, or procedures to make proper decisions or to carry them out in the time available.
Automated features of flight control systems can improve situational awareness by reducing crew workload. However, automated actions that compensate for unusual flight conditions or equipment malfunctions can reduce situational awareness if the automated system masks the presence of abnormalities or does not clearly indicate what actions it is taking in response.
Aircraft must be designed so that, for all situations the flight crew can reasonably be expected to encounter, it will have the data it needs in an easily recognizable form that facilitates proper decision making. Furthermore, the aircraft should be designed to help the flight crew carry out necessary tasks, especially in emergencies when things are not as
expected and safety depends on quick and correct actions by the flight crew. Except for the time pressure typically associated with in-flight emergencies, the same considerations apply to the actions of maintenance personnel.
CURRENT INITIATIVES TO REDUCE ACCIDENTS AND INCIDENTS ASSOCIATED WITH HUMAN ERROR
Many aspects of human factors are associated with the operational safety of commercial airplanes, including the following:
design factors associated with aircraft controls, aircraft system controls, warning systems, air traffic control systems, flight deck, passenger seating and egress, etc.
operational factors associated with the selection and training of flight crews, crew assignment policies related to the distribution of experienced personnel and the minimization of flight crew fatigue, checks on crew members' health, and policies on preflight information
maintenance factors related to training maintenance workers; the clarity of maintenance procedures; and designing aircraft equipment and maintenance tools to make it easier for workers to perform maintenance, avoid errors, and detect abnormal conditions
national and international regulatory factors associated with airworthiness standards, separation standards, and communications standards
Current processes, which are both thorough and complex, have resulted from a large accumulation of flight experience, analytical and computer studies, and reviews of human factors. All of this information represents a complicated web of interrelated factors that makes it difficult to define a clear and simple road map for progress. Complexity, however, is inherent in many human factors issues.
Figure 5-2 provides a greatly simplified view of human factors initiatives related to aviation. A much more detailed picture of the breadth and depth of current work and what needs to be done is available in the following publications:
The detailed report of the FAA Human Factors Team, Interfaces Between Flight Crews and Modern Flight Deck Systems (1996), includes more than 50 well formulated recommendations.
The Proceedings of the FAA Workshop on Flight Crew Accident and Incident Human Factors (1995) explores three human factors objectives.
The April 1997 International Symposium on Aviation Psychology includes more than 300 papers on human factors associated with flight safety.
The National Aeronautics and Space Administration report, Principles and Guidelines for Duty and Rest Scheduling in Commercial Aviation (1996), defines numerous general principles, specific principles, guidelines, and strategies for improving duty and rest scheduling practices.
The NTSB review, Flight-Crew-Involved Major Accidents of U.S. Air Carriers, 1978 through 1990 (1992), includes five broad recommendations.
Human Factors Guide for Aviation Maintenance (FAA, 1997), published by the FAA's Office of Aviation Medicine, presents basic concepts on reducing human errors in maintenance.
A video tape, ''Every Day: A Programme about Error Management in Aircraft Maintenance,'' developed and published by the International Federation of Airworthiness (1997), features Professor James Reason and reviews human factor issues related to maintenance.
Additional work in fields such as cognitive science and fundamental neuroscience is progressing rapidly and is likely to offer valuable insights in the near future. The potential benefits of relying more on cognitive science are explained by James Reason (1990) and, in a more philosophical sense, by David Chalmers (1996). Turning to cognitive science to improve the understanding of issues associated with situational awareness has two major advantages. First, it should encourage the development of processes and systems that would improve the selection and presentation of necessary information, assigning to automated systems the tasks that systems do best and allowing people to continue doing the tasks that people do best. Second, it should help define the type of automation that can reduce the workload of flight crews and air traffic controllers in the crucial moments when a situation must be assessed quickly and accurately.
IMPROVING THE EFFECTIVENESS OF THE FAA'S HUMAN FACTORS PROJECTS
Harnessing the growing body of human factors knowledge will enhance the FAA's efforts to reduce the number of incidents and accidents by reducing human error and improving the ability of flight crews and other personnel to prevent accidents associated with other causes. That is one of the tasks of the FAA's Human Factors Study Group. This group appears to be reasonably well coordinated with the JAA (Joint Aviation Authorities) Human Factors Study Group and will operate indefinitely. Close coordination between these two groups is important in an environment that is becoming increasingly aware of the value of international harmonization of airworthiness standards and procedures. Coordinating the work of both groups with similar study groups sponsored by ICAO and other certifying authorities would also be worthwhile.
The membership of the FAA Human Factors Study Group should be reviewed and adjusted, if necessary, to ensure that it has strong representation from the fields of cognitive science and basic neuroscience. Strong representation in these areas would help the study group form a cohesive framework for understanding the very large number of human factors studies that are now under way, and it would enhance the ability of the group to recommend actions based on the results of these studies. Some of these studies are associated with enhanced ground proximity warning systems, improved traffic collision avoidance systems, and other aspects of developing crew-centered cockpit designs.
Finding 5-1. Maintaining situational awareness is the key to preventing the vast majority of serious incidents and accidents associated with human error.
Major Recommendation 4. The FAA should support and accelerate efforts (1) to define the minimum data required by the flight crew to maintain adequate situational awareness during all phases of flight and reasonable emergency scenarios and (2) to determine how this data can be presented most effectively.
Recommendation 5-1. The FAA should ensure that its human factors projects, especially the FAA Human Factors Study Group, include strong representation in the fields of cognitive science and basic neuroscience.
Recommendation 5-2. Advances in understanding human factors should be quickly applied to the key task of reducing the role of human errors in incidents and accidents, particularly with regard to improving the situational awareness of operational personnel and improving the effectiveness of maintenance personnel. The FAA should strongly support its Human Factors Study Group and other projects that contribute to this task.
Chalmers, D. 1996. The Conscious Mind. Oxford, U.K.: Oxford University Press.
FAA (Federal Aviation Administration). 1997. Human Factors Guide for Aviation Maintenance. Washington D.C.: Office of Aviation Medicine, FAA.
FAA. 1996. The Interfaces Between Flight Crews and Modem Flight Deck Systems. Report of the FAA Human Factors Team. Washington, D.C.: FAA.
FAA. 1995. Proceedings of the FAA Workshop on Flight Crew Accident and Incident Human Factors. Washington, D.C.: Office of System Safety, FAA.
IFA (International Federation of Airworthiness). 1997. "Every Day: A Programme about Error Management in Aircraft Maintenance." Sussex, U.K.: IFA.
NASA (National Aeronautics and Space Administration). 1996. Principles and Guidelines for Duty and Rest Scheduling in Commercial Aviation. Washington, D.C.: NASA.
NTSB (National Transportation Safety Board). 1992. Flight-Crew-Involved Major Accidents of U.S. Air Carriers, 1978 through 1990. Washington, D.C.: NTSB.
Proceedings of the Ninth International Symposium on Aviation Psychology. April 28-May 1, 1997, Columbus, Ohio. Ohio State University: Aviation Psychology Laboratory.
Reason, J. 1990. Human Error. Cambridge, U.K.: Cambridge University Press.