rates, number of separate actions, etc.) are preferred to subjective data. However, much can be learned from subjective experiences, observations and opinions. Also, there may be cases when it may be difficult to collect precise objective data because of test setup limitations or other variables that cannot be controlled nor compensated for by the test team. Under such circumstances, subjective data alone may be used to show compliance to 14 CFR, part 23, § 23.1523. For evaluations where subjective data only is collected, the applicant should consider the qualitative rankings of the perceived workload factors listed in Appendix 2 as well as a class of observable pilot behaviors listed in Appendix 1. It is recommended, however, that a combination of all the methods (both objective and subjective) be employed. Each combination can provide valuable information about the adequacy of the interface, workload and the ability of pilots to understand and use the system. It is the responsibility of the certification authority to determine whether a system successfully meets this requirement. The determination should be based on a review of all data collected throughout the test program, with particular emphasis on the workload, duration of the task, uncompleted tasks, and error rates.
(2) Forms. Data collection forms, questionnaire development, rating scales and other test reporting details are described in Appendix 4, Recommended Test Plan Guidance and Data Collection Information.
e. Credit for Tests. Applicants should conduct cockpit design and pilot performance evaluations throughout the development of a new system or component. The FAA may grant credit for performing such tests if it can be shown the test was conducted on a conformed component/system. The conformity may be done following the test, although the applicant must substantiate the component or system used for the evaluation is the same conformed component/system. Well-conducted and documented evaluations of a system early in a program may reduce flighttesting and FAA involvement later in the certification program. Credit for such evaluations must be coordinated before such testing with the responsible FAA office or authorized representative.
7 (and 8)
Appendix 1 APPENDIX 1. PILOT BEHAVIOR ASSOCIATED WITH HIGH WORKLOAD A number of human behaviors that are typically associated with high workload and they are listed below. The test conductor/observer should be especially cognizant of these behaviors during the conduct of the test and pay particular attention as to when and under what conditions any of these behaviors are observed. If any of these behaviors are observed during the course of the evaluations, more detailed examinations of workload may be necessary.
1. Observed learning behaviors
a. Pilot expends excessive effort to learn use of equipment
(1) Requires substantial assistance
(2) Repeatedly refers to training material
b. Pilot requires extended time period to become familiar with operation
c. Memory requirements are excessive
(1) Makes repeated reference to manuals throughout training for procedures
(2) Difficulty finding functions within menus
(3) Difficulty in returning to initial display page, mode, etc.
2. Observed cockpit operational behavior
a. Repeatedly refers to manuals or handbooks
b. Makes repeated unsuccessful attempts to enter or alter data
c. Exhibits excessive head-down time
(1) Break-down of normal scan
(2) Fixation on single display or interface
(3) Insufficient monitoring of surrounding airspace in VMC
d. Insufficient monitoring of cockpit displays
e. Performs task shedding
(1) Multiple concurrent tasks are not all performed (i.e., fails to perform checklist items)
(2) Overuse of automation to maintain performance
(3) Communications tasks
(a) Responses are monosyllabic
(b) Not all communications are acknowledged
(c) Read-backs are incorrect A1-1
Appendix 1 APPENDIX 1. PILOT BEHAVIOR ASSOCIATED WITH HIGH WORKLOAD (CONTINUED)
(d) Pilot misses communications
f. Commits errors
(1) Discrete
(a) Errors of commission (e.g., selects incorrect mode)
(b) Errors of omission (e.g., fails to engage mode when required)
(2) Continuous
(a) Course tracking errors
1. Vertical (altitude)
2. Horizontal (lateral and/or overshoot errors)
g. Exhibits signs of stress or fatigue
(1) Unable to respond to critical items in a timely fashion
(2) Indecisive (prolongs decisions or is unable to make them)
(3) Inattentive (fails to respond to events)
(4) Consistently asks for verbal communications to be repeated
(5) Unfocused (e.g., unable to concentrate on a single task to completion) A1-2
_______________________________________________________________________ Appendix 2 APPENDIX 2. MINIMUM FLIGHT CREW RULE The following restates the contents of 14 CFR part 23, § 23.1523 regarding workload determination:
The minimum flight crew must be established so that it is sufficient for safe operations considering –
(a) The workload of individual crewmembers, and in addition, for commuter category airplanes, each crewmember workload determination must consider the following:
(1) Flight path control.
(2) Collision avoidance.
(3) Navigation.
(4) Communications.
(5) Operation and monitoring of all essential airplane systems,
(6) Command decisions, and
(7) The accessibility and ease of operation of necessary controls by the appropriate crewmember during normal and emergency operations when at the crewmember flight station.
(b) The accessibility and ease of operation of necessary controls by the appropriate crewmember and;
(c) The kinds of operation authorized under 23.1523.
WORKLOAD FACTORS (reference AC 23-8B, Flight Test Guide for Part 23 Airplanes) The following is a listing of recognized workload factors considered significant when analyzing and demonstrating workload for minimum flight crew determination:
1. The impact of basic airplane flight characteristics on stability and ease of flight path control. Some factors such as trimmability, coupling, response to turbulence, damping characteristics, control breakout forces and control force gradients should be considered in assessing suitability of flight path control. The essential elements are the physical effort, mental effort and time required to track and analyze flight path control features, and the interaction with other workload functions.
2. The accessibility, ease, and simplicity of operation of all necessary flight, power, and equipment controls, including emergency fuel shutoff valves, electrical controls, electronic controls, pressurization system controls, and engine controls.
3. The accessibility and conspicuity of all necessary instruments and failure warning devices such as fire warning, electrical system malfunction, and other failure or caution indicators. The extent to which such instruments or devices direct the proper corrective action is also considered.
4. The complexity and difficulty of operation of the fuel system, with particular consideration given to the required fuel management schedule necessitated by e.g. structural, or other airworthiness considerations. Additionally, the ability of each engine to operate continuously from a single tank or source that is automatically replenished from other tanks if the total fuel supply is stored in more than one tank.
5. The degree and duration of concentrated mental and physical effort involved in normal operation and in diagnosing and coping with malfunctions and emergencies, including accomplishment of checklist, and location and accessibility of switches and valves.
6. The extent of required monitoring of the fuel, hydraulic, pressurization, electrical, electronic, deicing, and other systems while en route and recording of engine readings, and so forth.
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Appendix 2 APPENDIX 2. MINIMUM FLIGHT CREW RULE (CONTINUED)
7. The degree of automation provided in the event of a failure or malfunction in any of the aircraft systems. Such automation should ensure continuous operation of the system by providing automatic crossover or isolation of difficulties and minimize the need for flight crew action.
8. The communications and navigation workload.
9. The possibility of increased workload associated with any emergency that may lead to other emergencies.
10. Passenger problems.
11. Incapacitation of a flight crewmember whenever the applicable operating rule requires a minimum flight crew of at least two pilots.
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Appendix 3 APPENDIX 3. WORKLOAD EVALUATION ANNOTATED REFERENCES
1. PURPOSE. The purpose of this appendix is to provide a definition of workload and discuss the relationship of workload and performance. The remainder of the appendix provides an annotated bibliography of the literature on this topic.
a. Definition of Workload. Workload is a term used to describe the relationship between an individual's capacity to perform a task (mental and/or physical), and the level of system and situational demands associated with the performance of that task. The basic notion is related to the differences between the amount of resources available in the human operator and the amount of resources demanded by the task. Tasks that demand much of the human resources (capacity) are considered high workload tasks. Conversely, tasks that demand little of the human resources (capacity) are considered low workload tasks.
b. Performance and Workload. The relationship between workload and performance generally follows an inverted U-shaped curve, such that performance suffers if workload is either too high or too low. Levels of workload that are too low are often found in fully automated systems where the operator serves largely as a monitor of the automated processes. In these cases the operator/pilo t may become inattentive and/or bored, and this situation is generally referred to as task underload. At the opposite extreme, levels of workload that are too high often cause the pilot to miss important information, fail to perform tasks, make errors or engage in task shedding in an attempt to reduce workload. Although automation is generally employed to and thought to decrease pilot workload, in some cases it has either had little effect or actually increased workload. While the automation may relieve the pilot from the performance of the automated tasks, it may impose additional task requirements related to operating the automated functions. One difficulty found in highly automated systems is that when the automation fails, pilot workload can be significantly increased. Specific attention should be given to the relative ease or difficulty with which the pilot can detect changes in or extract information about system status.
A key goal of the system designer is to find the middle ground such that the pilot is sufficiently engaged in the process to remain alert and involved in system operation yet not so loaded as to be incapable of performing all of the necessary tasks in an efficient and timely fashion. Additionally, the analysis of workload must be extended to include the case where automation fails, and the pilot must now perform those functions. Therefore, the introduction of new integrated complex avionics systems, whether highly automated or not, needs to be evaluated and should also include an examination of human error.
c. Workload and Error. Human error is often related to workload, and there is usually a positive correlation between excessive workload and the occurrence of errors. It should be noted that errors could also be associated with low workload. When recording flight crew error, please refer to list of annotated references on this topic. The references describe methods and data collection techniques that can be used in the evaluation.
When collecting data the pilot's performance should be quantified in terms of:
(1) Number of errors committed
(2) Consequences of errors
(3) Time spent recovering from errors
(4) Number of subsequent incorrect actions due to the error
(5) Time spent using manuals to recover from errors.
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Appendix 3 APPENDIX 3. WORKLOAD EVALUATION ANNOTATED REFERENCES (CONTINUED) Annotated References Selecting Performance Measures
1. Kantowitz, B.H. (1992). Selecting measures for human factors research. Human Factors, 34(4), 387-398.
Selecting measures is a necessary component of human factors research. Proper selection must take into account the representation problem (how is the assignment of numbers to objects or phenomena justified?)
and the uniqueness problem (to what degree is this assignment unique?). Other key human factors measurement issues include subject representativeness, variable representativeness, and setting representativeness. It is difficult to create a single measure that captures essential characteristics of complex systems. Several examples illustrate how theory can guide measurement selection in such diverse human factors research as vigilance, turning off warning alarms, information requirements for military command centers, subjective workload, heart-rate signal analysis, and heat stress in nuclear power plants.
Measurement and Assessment Techniques
1. Assessment of crew workload measurement methods, techniques and procedures.
Volume 1, Process, methods and procedures; Volume 2, guidelines for the use of workload assessment techniques in aircraft certification.
Volume 1 states that the goal of this document is to “identify assessment techniques which demonstrate evidence of validity and reliability and are suitable as measures of flightcrew workload for certification.
This document was sponsored by the FAA and was a two-year effort. Testing was done via simulation and used various measures including SWAT, NASA TLX, and Bedford rating scales. Timeline analysis was used to identify high and low task demand levels. Volume 2 contains basic information on how to gather workload data.
2. Casali, J.G. and Wierwille, W.W. (1983). A comparison of rating scale, secondary-task, physiological, and primary-task workload estimation techniques in a simulated flight task emphasizing communications load.
Human Factors, 25(6), 623-641.
Sixteen potential metrics of pilot mental workload were investigated regarding their sensitivity to communication load and their intrusion on primary task performance. A moving-base simulator was used to present three cross-country flights. The flights varied only in the difficulty of the communications requirements. Results indicated that both the Modified Cooper-Harper Scale and the workload Multidescriptor Scale were sensitive to changes in communications load. The secondary-task measure of time estimation and the physiological measure of pupil diameter were also sensitive. As expected, those primary-task measures that were the direct measure of communicative performance were also sensitive to load, whereas aircraft control primary-task measures were not, attesting to the task specificity of such measures.
3. Gawron, V.J., Schiflett, S.G., and Miller, J.C. (1989). Measures of in-flight workload. In R.S. Jensen (Ed.)
Aviation Psychology. Aldershot, Haunts, UK: Gower Publishing Company.
This reference contains a review of empirical measures of workload that can be used during flight test. The review includes a general description of the workload measures, associated strengths and weaknesses, and guidelines for use. The chapter also includes a discussion of workload validation studies.
4. Gawron, Valerie J. (2000). Human Performance Measures Handbook. Mahwah, New Jersey: Lawrence Erlbaum Associates.
Drawing from her work testing and evaluating projects of military and commercial transportation systems, Gawron offers help to both the novice and the experienced in selecting measures to be used to evaluate A3-2
Appendix 3 APPENDIX 3. WORKLOAD EVALUATION ANNOTATED REFERENCES (CONTINUED) human/machine systems. The handbook begins with an overview of the steps involved in developing a test to measure human performance, workload, and/or situational awareness. This is followed by a definition of human performance and a review of human performance measures. It is a unique reference covering the basics of measures as well as authoritative summaries of over 100 performance, workload, and situational awareness measures. It is an excellent desktop reference for designers, test and evaluation specialists, and system specification developers.
5. Gopher, D., and Donchin, E. (1986). Workload--An examination of the concept. In K. Boff and L. Kauffman (Ed.s), Handbook of perception and human performance. New York: Wiley and Sons, chapter 41, pp. 1-
49.
This chapter represents a theoretical examination of the multidimensional, multifaceted concept of workload. Due to the complexity of the construct, no single measure is capable of capturing all relevant aspects, nor may multiple measures covary within a single task. The discussion was concerned with clarifying the nature of the dimensions along which workload varies to explicate the attributes that should be considered in the selection of a measurement procedure. The primary thesis is that workload assessment focuses on measuring the processing and response limitations of the human information processing system which are revealed through the interactions between an operator and the assigned tasks. The nature of the limitations were considered on two levels: (1) the more theoretical level (in which the invariant, open loop properties of the human processing system were examined), and (2) a more practical level (in which workload was characterized, at any instant, as the joint, closed loop property of the human and the assigned task). In general, the focus of the theoretical discussions emphasized the close affinity between the study of workload and attention, with an additional discussion of the energetical and structural characteristics of the central processor. The recommendation was made that measurement procedures should encompass both conscious and non-conscious processing activities; a detailed task analysis should be performed to uncover the major components of the task, followed by a battery of performance-based measures designed to evaluate the load on each component.
6. Hart, S. G. (1986). Theory and measurem ent of human workload. In J. Zeidner (Ed.), Human productivity enhancement: Training and human factors in system design (pp. 396-456). New York: Praeger.
The goal of this reference is to define human workload, what influences it, how it is measured, and why it is of theoretical and practical concern. The first section reviews typical definitions and motives for measuring and predicting workload. A structure is proposed to relate and integrate many of the factors that create or influence it (e.g., the experiences of operators). A third section describes five types of assessment and predictive methodologies: (1) subjective ratings, (2) primary task performance, (3) secondary task performance, (4) physiological recordings, and (5) analytic procedures. Finally, the selection and application of appropriate tools to predict or assess imposed workload, system performance and behavior, or operator experience is considered.
7. Hart, S. G. (1987). Research papers and publications (1981-1987): Workload research program (NASA Technical Memorandum 100016). Washington, DC: National Aeronautics and Space Administration.
This document contains an annotated bibliography of the research reports written by participants in NASA's Workload Research Program from 1981 to 1987. It represents the results of theoretical and applied research conducted at Ames Research Center and at universities and industrial laboratories funded by the program. The major program elements include: (1) developing a fundamental understanding of the concept of workload, (2) providing valid, reliable, and practical measures of workload, and (3) creating a computer model to predict workload. The overall goal is to provide workload-related design principles, measures, guidelines, and computational models. The research results are transferred to user groups by establishing close ties with manufacturers, civil and military operators of aerospace systems, and regulatory agencies; publishing scientific articles; participating in and sponsoring workshops and symposia; providing information, guidelines, and computer models; and contributing to the formulation of standards. In A3-3
Appendix 3 APPENDIX 3. WORKLOAD EVALUATION ANNOTATED REFERENCES (CONTINUED) addition, the methods and theories that have been developed have been applied to specific operation and design problems at the request of a number of industry and government agencies.
8. Hart, S.G., and Staveland, L.E. (1988). Development of NASA-TLX (Task Load Index): Results of empirical and theoretical research. In P.A. Hancock, and N. Meshkati (Eds), Human Mental Workload, 139-183. North Holland, Amsterdam: Elsevier.
Abstract: The results of a multi-year research programme to identify the factors associated with variations in subjective workload within and between different types of tasks are reviewed. Subjective evaluations of 10 workload-related factors were obtained from 16 different experiments. The experimental tasks included simple cognitive and manual control tasks, complex laboratory and supervisory control tasks, and aircraft simulation. Task, behaviour and subject-related correlates of subjective workload experiences varied as a function of difficulty manipulations within experiments, different sources of workload between experiments, and individual differences in workload definition. A multi-dimensional rating scale is proposed in which information about the magnitude and sources of six workload-related factors are combined to derive a sensitive and reliable estimate of workload.
9. Kantowitz, B.H., and Casper, P.A. (1988). Human Workload in Aviation. In E.L. Wiener and D.C. Nagel (Eds.), Human Factors in Aviation. San Diego: Academic Press, Inc.
In Kantowitz and Casper's chapter on Human Workload in Aviation a wide variety of approaches to measuring workload are described, and empirical studies using these methods are reviewed. The importance of the concept of workload and the challenges of defining this hypothetical concept are reviewed. The authors relate workload to the psychological concept of attention, and suggest how theoretical models of attention can provide insight to the problem of measuring human workload in air traffic control and cockpit applications.
10. National Test Pilot School course “human factors and workload” (minimum flight crew) This course is taught at the National Test Pilot School in Mojave, CA. It was developed in the early 80's as a result of changes to the minimum flight crew rule and development of AC 25.1523 for Part 25 operations.
This course was intended to raise the level of awareness and the importance of workload evaluations that were being conducted by the certification test pilot community. FAA and non-FAA evaluators receive this training and instruction materials when they attend the course.
11. Ogden, G.D., Levine, J.M., and Eisner, E.J. (1979). Measurement of Workload by Secondary Tasks. Human
Factors, 21(5), 529-548.
The post-1965 literature on the use of secondary tasks in the assessment of operator workload was surveyed. Twelve classes of tasks were identified; the most frequently used were choice reaction time, memory, monitoring, and tracking. The literature review did not suggest a single best task or class of tasks for the measurement of workload. Limitations in using secondary tasks are discussed, and directions for future research are presented.
12. Rehmann, J.T., Stein, E.S. and Rosenberg, B.L. (1983). Subjective pilot workload assessment. Human Factors, 25(3), 297-307.
Compared workload ratings done after the simulator flight with those done periodically during the flight.
An auditory prompt was sounded once per minute and the pilot was required to enter a workload rating on a scale of one through ten using a numeric keypad. They found that ratings done during the flight most accurately reflected the difficulty of that flight and that the latency of pilot response to the auditory prompt was positively correlated with the difficulty of the task (responses were slower when workload was rated as high).
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Appendix 3 APPENDIX 3. WORKLOAD EVALUATION ANNOTATED REFERENCES (CONTINUED)
13. Sirevaag, E., Kramer, A., Wickens, C., Reisweber, M., Strayer, D., and Grenell, J. (1993). Assessment of pilot performance and mental workload in rotary wing aircraft. Ergonomics, 36, 1121-1140.
This research examined the processing demands imposed upon experienced pilots by two different communication formats, digital and verbal, in a high fidelity simulation of an advanced multi-function helicopter. The mental workload imposed by the type and magnitude of communications was assessed by a battery of subjective, performance, secondary, and physiological measures. The results are discussed in terms of the structural and capacity demands of the communications systems that were proposed for the advanced multi-function helicopter.
14. Vidulich, M.A. and Tsang, P.S. (1986). Techniques of subjective workload assessment: A comparison of SWAT and the NASA Bipolar Method. Ergonomics, 29 (11), 1385-1398.
Two techniques for assessing subjective workload, the Subjective Workload Assessment Technique (SWAT) and the NASA Bipolar method, were applied in a laboratory experiment that required the rating of a number of single- and dual-tracking and spatial transformation tasks. Both subjective assessment techniques displayed similar sensitivity to the different task manipulations. SWAT assesses subjective workload in terms of time load, mental effort load and psychological stress load. The NASA Bipolar method assesses subjective workload in terms of task difficulty, time pressure, performance, mental/sensory effort, physical effort, frustration, stress, fatigue and activity type. The purpose of the study was to compare the merits of the two techniques.
15. Vidulich, M.A., Ward, G.F., and Schueren, J. (1991). Using the Subjective Workload Dominance (SWORD) Technique for projective workload assessment. Human Factors, 33(6) 677-691.
This study examined the utility of the Subjective Workload Dominance (SWORD) technique as a projective workload tool. Two groups predicted the workload associated with using six possible head-up display formats. The projective ratings from the groups were correlated with retrospective ratings from another group that had experienced all six formats in a simulator study. The results support the utility of the SWORD technique as a projective tool, provided a group of subject matter experts is available to make the required judgments.
16. Virzi, R. A. (1992). Refining the test phase of usability evaluation: How many subjects is enough? Human Factors, 34(4), 457-468.
(a) 80 percent of the usability problems are detected with 4 or 5 subjects, (b) additional subjects are less and less likely to reveal information, and (c) the most severe usability problems are likely to have been detected in the first few subjects. Formulas are provided for calculating the number of subjects needed for a given level of confidence.
17. Williges, R.C. and Weirwille, W.W. (1979). Behavioral measures of aircrew mental workload. Human Factors, 21, 549-574.
Behavioral research literature pertaining to the measurement of aircrew workload was classified into general categories of subjective opinion, spare mental capacity, and primary task metrics. Fourteen specific classes of workload measures related to these general categories were reviewed specifically with regard to aircrew workload assessment. Each class of measures was summarized in terms of background, applications, and implications for research and implementation. Due to the multidimensionality of workload, it was concluded that the most promising assessment procedure should include multiple measures of subjective opinions, spare mental capacity, and primary task measures as well as physiological correlates.
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Appendix 3 APPENDIX 3. WORKLOAD EVALUATION ANNOTATED REFERENCES (CONTINUED)
18. Wierwille, W.W. and Conner, S.A. (1983). Evaluation of 20 workload measures using a psychomotor task in a moving-base aircraft simulator. Human Factors, 25(1), 1-16 Examined 20 workload measures using a psychomotor task with 3 levels of psychomotor load.
Sensitivities of workload techniques vary and only a few of the techniques tested appeared to be sensitive to psychomotor load. Provides suggestions for how to select a workload estimation technique for specific tasks. Used instrument approach and landing as task. Looked at these categories of assessment techniques:
opinion, spare mental capacity, physiological measures, and eye behavior. Primary task performance indicated which techniques were most sensitive to workload manipulations.
19. Wierwille, W.W., Rahimi, M., and Casali, J.G. (1985). Evaluation of 16 measures of mental workload using a simulated flight task emphasizing mediational activity. Human Factors, 27(5), 489-502.
Presented evaluation of 16 mental workload measures applied to mediational piloting tasks (defined as activities related to logic, reasoning, decision-making and judgment). Identifies which measures were sensitive to mediational workload, which ones were not, and which measures were intrusive.
Comparison of Workload Measures
1. Hankins, T.C. and Wilson, G.F. (1998). A comparison of heart rate, eye activity, EEG, and subjective measures of pilot mental workload during flight. Aviation, Space, and Environmental Medicine. 69(4), 360-367.
Cardiac, eye, brain and subjective data were collected during an actual flight scenario designed to present pilot subjects with tasks requiring different piloting skills at several levels of mental workload. Results from these methods were compared and suggest that while subjective estimates provide useful information about pilot workload, multiple measures, especially psychophysiological measures (cardiac, respiratory, eye, brain and hormonal measures), provide a more comprehensive picture of the mental demands of flight.
The measures used in this study provided unique, non-overlapping information.
2. Hicks, T.G. and Wierwillie, W.W. (1979). Comparison of five mental workload assessment procedures in a moving-base driving simulator. Human Factors, 21(2), 129-143.
Examined five methods of measuring workload in a driving simulator (a psychomotor task): secondary tasks, occlusion techniques (forced time sharing by limiting the time that visual information could be viewed), physiological measures (cardiac arrhythmia), subjective opinion method, and primary task performance. Primary task and rating scale appeared to be the most sensitive for this application.
3. Hill, S.G., Iavecchia, H.P., Bittner, A.C. Jr., Zaklad, A.L., and Christ, R.E. (1992). Comparison of four subjective workload rating scales. Human Factors, 34(4), 429-439.
Four subjective workload scales were compared along four dimensions: sensitivity, operator acceptance, resource requirements, and special procedures. The scales were the Modified Cooper-Harper scale, the National Aeronautics and Space Administration Task Load Index (TLX), the Overall Workload (OW) scale, and the Subjective Workload Assessment Technique. Three U.S. Army systems were studied for potential workload concerns. Data from five different studies on the three systems were compared along the aforementioned four dimensions. Results indicate that all four scales are acceptable tools and are sensitive to different levels of workload. However, TLX and OW are consistently superior when considering sensitivity, as measured by factor validity and operator acceptance. TLX and SWAT may help identify the causes of excessive workload and ways to alleviate it.
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