Mental Workload Assessment In Military Pilots Using Psychophysiological Measures In Flight

Mental workload is defined as the physiological and mental demands that occur while performing a task or a combination of tasks. Mental workload is not an inherent property, but rather it emerges from the interaction between the requirements of a task, the circumstances under which it is performed, and the skills, behaviors, and perceptions of the operator. Pilots in modern military flight systems have to process a considerable amount of complex information, much more comprehensive than in older systems. The information and decision making processes have become more and more demanding and the risk of mental overload has increased. Furthermore, any mistake by pilots could lead directly to a serious accident or at least a dangerous situation. Not only is pilot under mental stress but also physical stress as well, i.e. changes in acceleration, atmospheric pressure, vibration and temperature. Therefore, the pilot is considered to be under workload at whole flight course.The need to assess pilot workload during flight has become an important factor in the development of new aircraft, support systems and operating procedures. This applies both to combat aircraft, where the success of the mission may be compromised by excessive workload, and to civil transport, where the increasing use of automation may lead to underload and complacency and thus reduce levels of safety.Human factors are identified broadly as contributing to most aircraft accidents. Although percentages vary, most would agree that somewhere between 60%-80% of aviation accidents are due, at least in part, to human error, especially in the phases of take-off, instrument or manual approach and landing, when mental overload occurs. Mental overload directly affects human performance and threats to flight safety. Assessment of pilot mental workload is, therefore, an important aviation management issue, as enhancing flight performance and ensuring flying safety are considered.There is general agreement that in-flight mental workload is a multidimensional construct, and a lack of standardized and accepted assessment techniques makes it difficult to measure. Psychophysiological measurements are of particular importance in the flight environment since they offer a non-intrusive method to collect objective data about the mental workload of pilots and other crew members. A benefit of psychophysiological measurements is their potential sensitivity over the entire workload range from underload to overload. An increase in workload results in an increase of HR, whereas HRV decreases.Subjective rating scales, such as multidimensional NASA-TLX, are the most widely used workload assessment tools. The advantages of subjective workload assessments are ease of implementation, low cost, and limited intrusion on task performance. Rating scales generally provide a good indication of the total workload.Measurement of mental workload has been widely used for evaluation of aircraft design, mission analysis and assessment of pilot performance during flight operations. Research on mental workload in West has been carried on for more than twenty years while in our country it is just underway, most of which was experimental or flight simulator study, but little real flight assessments reported.In order to evaluated in-flight mental workload of military pilots of various kinds of flight course and flight phase, in the present study psychophysiological measures were obtained while different grades of fighter pilot performed real traffic pattern flight tasks and basic acrobatic flight tasks, and we also performed subjective workload assessment of three flight phases using modified NASA-TLX on military helicopter pilots after instrument flight.The main findings are as follows:1. Feasibility study of the changing in-flight physiological parameters of fighter pilot match exactly with changing flight status parameters.In the present study, three fighter pilots were investigated while performing routine flight training. ECG, respiration wave, body temperature, body movement and acceleration (Gz & Gx) were continuously measured and analyzed using a small recording device strapped around the chest. The flight parameters, critical event as well as flight path of each flight were recorded using flight parameters recorder during the real flight and analyzed after all flight procedures performed. The instantaneous heart rate and respiration rate of any flight status can be differentiated and determined through analysis flight parameters recorded using flight parameters recorder. Time-domain analysis and frequency-domain analysis of short-time rapid HRV can be matched with different flight phases. This study provides an available technique to analyze exactly in-flight psychophysiological parameters and to measure mental workload dynamically.2. Mental workload assessment in fighter pilots using psychophysiological measure in traffic patterns flight.There were 11 experienced fighter pilots (flight instructors) and 10 less experienced novice fighter pilots on active flying status who participated in this study. The subjects performed four uninterrupted traffic patterns flight missions with two-seat jet trainers, an experienced pilot seated in rear seat and a novice pilot seated in front seat. The psychophysiological parameters were continuously measured using a small recording device strapped around the chest. Heart rate, respiration rate, time-domain analysis and frequency-domain analysis of short-time rapid HRV (1.5 min) in different flight phases were compared and mental workload were analyzed.During take-off and climb phases, heart rates and respiration rates of novice fighter pilots were significant higher, while SDNN, RMSSD, TINN, TP and LF of them were significant lower than those during preflight baseline, but in flight instructors, only respiration rates was significant higher, while SDNN, TINN and LF were found reduced significantly as compared with preflight. Heart rates of novice fighter pilots were significant higher than those of flight instructors. During the phase of cruising on downwind leg, heart rates, SDNN, RMSSD, RMSSD and TINN in both groups were returned to level of preflight baseline; however, respiration rates in novice fighter pilots were still higher than those of preflight. During approach to landing phase, heart rates and respiration rates were significant higher, while SDNN, TINN and LF were significant lower than those of preflight baseline in both groups. RMSSD and HF reached their lowest values, but LF/HF reached its highest value in both groups, there were significant differences in HF and LF/HF of flight instructors as compared with preflight.The changes of psychophysiological data in both groups reflect enhancement of mental workload in take-off and climb phase, somewhat depress (but still high) in phase of cruising on downwind leg, and again enhancement (to highest level) of mental workload and stress state during approach to landing phase. The results also indicate that, mental workload among novice fighter pilots were greater than those of flight instructors during take-off and climb phase, however, during approach to landing phase the case was the opposite, mental workload of flight instructors were greater than those of novice fighter pilots.3. Mental workload assessment in fighter pilots using psychophysiological measures in basic acrobatic flight.The psychophysiological parameters were continuously measured in 10 fighter pilots (flight instructors) and 10 novice fighter pilots during basic acrobatic flight missions with two-seat jet trainers. During the flight, instructor seated in rear seat and novice pilot seated in front seat. Heart rate, respiration rate, time-domain analysis and frequency-domain analysis of short-time rapid HRV (1.5 min) in different flight phases were compared and mental workload were analyzed.Heart rates in both groups were significant higher than those of preflight baseline during the course of acrobatic flight, in phase of return to base, showed somewhat fallback, and in phase of approach to landing again increased significantly. During the course of performing acrobatic maneuvers, higher respiration responses were observed among novice fighter pilots; while in flight instructors, respiration rates were significant lower than those of novice fighter pilots. During circle with 60-degree bank angles, splits, somersault, hemi-somersault rollover flight phases, SDNN, RMSSD, TINN, HF and HF norm in both groups were significantly reduced; LF, LF norm, LF/HF were significantly increased. During the phase of return to base, HF in both groups was enhanced in some degree; in this phase, LF norm of novice fighter pilots was significant higher than that of flight instructors, but HF norm was significant lower than the latter group. The flight instructors SDNN value reached to its lowest level during approach to landing phase, but in novice fighter pilots, the lowest value of SDNN was seen in the take-off and climb phase. During approach to landing phase, TP of flight instructors were significant lower, and LF/HF of them were significant higher than those of preflight baseline; as compared with novice fighter pilots, RMSSD of flight instructors were significant lower in this phase.The findings suggested that two group fighter pilots have high mental workload during circle with 60-degree bank angles, splits, somersault, hemi-somersault rollover flight phases, no difference in mental workload were found between the two groups. Psychophysiological data in both groups during phase of return to base reflect relative mitigation of mental workload, and novice fighter pilots'mental workload was relative lower than that of flight instructors. The results also indicate different mental workload represents in the two groups during take-off and climb phase and during approach to landing phase, i.e. relative high workload during take-off and climb phase and relative low workload during approach to landing phase for novice fighter pilots; relative low workload during take-off and climb phase and relative high workload during approach to landing phase for flight instructors.4. Mental workload assessment of helicopter pilots in instrument flight with subjective-ratings measurementsIn order to evaluated in-flight mental workload of helicopter pilots. Fifteen male military helicopter pilots from a corps participated in this study. Flight mission was instrument flight. At the end of the flight, subjective mental workload assessment for three different flight phases were rated using multidimensional subjective measures (i.e., modified NASA-TLX questionnaire). The overall TLX subjective workload ratings scores for the take-off, cruise, and landing phases were 34.46±17.25, 32.11±13.11, 53.95±17.76, respectively. The landing TLX scores were significant higher in comparison with take-off and cruise phases. Significant negative correlations between flight hours and subjective workload ratings scores were noted for the three flight phases. During the take-off phase coefficient of correlation between flight hours and subjective workload ratings scores was -0.810 (p < 0.01) and the linear regression equation of the two variables was: TLX scores = 42.20– 0.01203×flight hours. During the cruise phase, coefficient of correlation between flight hours and subjective workload ratings scores was -0.535 (p < 0.05) and the linear regression equation of the two variables was: TLX scores = 38.51–0.00604×flight hours. During landing phase, coefficient of correlation between flight hours and subjective workload ratings scores was -0.532 (p < 0.05) and the linear regression equation of the two variables was: TLX scores = 62.57– 0.00814×flight hours. Analysis of the TLX scores for our participants reveals that the subjective mental workload is higher during landing phase as compared with other phases. The results also indicate that, subjective in-flight mental workload is alleviative with the accumulation of flight experience.