No description available.

No description available.

Human information processing consists of multiple and limited resources; some of them are shared while some are separate and non-interchangeable. High pilot mental workload (PMWL) - and the subsequent decline in performance - results from the imbalance between the mental resources available to perform the task and the amount of resources needed to perform it. When the pilot’s proficiency is evaluated, s/he should deliver an acceptable performance while being able to reserve enough mental capacity for the unexpected, additional resource demands. The task demands and cognitive stressors of air combat have potential to degrade pilot performance to an unacceptable level. Therefore, it is important to understand the amount of mental workload the pilots are experiencing and how much spare capacity they have available to cope with the possible additional resource demands. This thesis was aimed at understanding the relationship between PMWL and performance. The approach presented in this thesis was expected to support the development of reliable metrics for predicting the pilot performance under the stress of combat. In terms of practical applications, this thesis contributed to the development of the methodological principles that could help assuring the pilots’ ability to cope with the task demands higher than those experienced during training or proficiency checks. Heart rate (HR) and heart rate variation (HRV) were used as indexes of PMWL. The selection was done for several reasons. HR and HRV measures were accepted by the pilots as they were non-intrusive and they appeared to be objective. In addition, the implementation requirements were by no means excessive. Considering the aims of this thesis, the low diagnosticity of HR/HRV was not an issue. Finally, HR and HRV proved to be sensitive measures of varying task demands – especially when measured together with the pilots’ awareness of the mission requirements. Simulated fighter missions were used to manipulate the pilots’ task demand and to measure their performance and HR/HR. The thesis is constructed around three studies. In the first study, the subjects were required to fly instrument approaches in a high fidelity simulator under various levels of task demand. The task demand was manipulated by increasing the load on the subjects by reducing the range at which they commenced the approach. HR and the time domain components of HRV were used as measures of PMWL. The findings indicated that HR and HRV were sensitive to varying task demands. HR and HRV were able to distinguish the level of PMWL after which the subjects were no longer able to cope with the increasing task demands and their performance fell to a sub-standard level. The major finding of the first study was the HR/HRV’s ability to differentiate the sub-standard performance approaches from the high performance approaches. In the second study, fighter pilots’ performance and PMWL were both measured during a real instrument flight rules proficiency check in an F/A-18 simulator. PMWL was measured using HR and HRV. Performance was rated using Finnish Air Force’s official rating scales. Results indicated that HR and HRV were able to differentiate varying task demands in situations where variations in performance were insignificant. It was concluded that during a proficiency check, PMWL should be measured together with the task performance measurement. In the third study, fighter pilots’ HRV and performance were examined during instrument approaches and air combat. The subjects’ performance was rated by a weapons instructor. In addition, the subjects’ HRV was measured and used as an indicator of PMWL. During the instrument approaches, low performance was associated with high PMWL as expected. However, during the combat phases of the mission, low performance was associated with low PMWL. When the subject’s awareness of the mission requirements was studied, it was found that the combination of low performance and low PMWL was associated with the subjects’ low awareness of the mission requirements. The major finding was that unless the subjects’ awareness of the mission requirements is examined, the relationship between the mental workload and performance during a complex combat mission may be difficult to explain. It is concluded that HR and HRV are sensitive measures of PMWL in a simulated fighter aviation environment. HR and HRV proved to be associated with the changes in task demands and pilots’ performance during simulated instrument approaches and air combat. However, the results of this thesis suggest that measuring just PMWL and performance is not sufficient – especially if the task of interest is complex and dynamic. To fully understand the pilot performance in such environment, the relationship between awareness of the mission requirements, workload and performance needs to be untangled. While this thesis provides encouraging results to understand this phenomena, further research is still needed before awareness of the situation requirements (or more broadly, situation awareness), performance and mental workload can be measured simultaneously, objectively and in real time.

Cockpit Task Management (CTM) is the initiation, monitoring, prioritization, execution, and termination of multiple, concurrent tasks by night crews. The primary research question posed in the current research is what factors affect task prioritization on the modern day, commercial flight deck. The conventional CTM literature was reviewed as an introduction to CTM validation, its facilitation and its theoretical foundations. A human performance approach to CTM was explored through experimental psychology literature, with the objective of developing a deeper understanding of the prioritization process. Two experimental part-task simulator studies were performed using commercial airline pilots. The objective of the first study was to simply identify possible prioritization factors. The second study then gathered empirical evidence for actual use of these factors. From the results, a model of task prioritization emerged with Status, Procedure and Value as the primary factors that affect task prioritization. / Graduation date: 2000

Piloting a commercial aircraft involves performing multiple tasks in a real-time environment that require pilot's attention and cognitive resource allocation. Due to resource limitation, pilots must perform cockpit task management (CTM) because they cannot perform all tasks that demand their attention at once. Hence, pilots must prioritize the tasks in the order of most to least important and allocate their resources according to this prioritization. Over the years, pilots have developed rules of thumb for task prioritization in facilitating CTM. A task prioritization error is simply an error made by the flight crew when they perform lower priority tasks as opposed to higher priority tasks, where priority is determined by the Aviate-Navigate-Communicate-Manage Systems (A-N-C-S) task ordering. Although the level of flight deck automation has been suggested as one factor influencing the likelihood of task prioritization errors, there has so far been just one study directed towards confirming that hypothesis. Hence the first objective of this study was to determine the effect of the level of automation on CTM performance. CTM performance was measured by looking at the number of task prioritization errors committed by pilots in different levels of automation. In addition to the level of automation, there was also reason to believe that the pilot's automation proficiency might affect CTM performance. Therefore, the second objective of this study was to determine the effect of automation proficiency on CTM performance. Nine airline transport pilots served as subjects in this study. Three flying scenarios and three levels of flight deck automation were simulated on a part-task flight simulator. Each pilot ran three different combinations of flight deck automation and flying scenario. The CTM performance for each pilot was determined by identifying the number of task prioritization errors committed in each experiment run. The average number of errors in different levels of automation and automation proficiency were compared for their effect on CTM performance using Analysis of Variance (ANOVA). It was found that the level of automation affected CTM performance depending scenarios in which phases of flight differed. However, automation proficiency, measured by glass cockpit hours, was found to have no effect on CTM performance. / Graduation date: 2000

Graduation date: 1995

A significant number of aircraft incidents and accidents have been caused, in part, by flightcrew failure to properly manage cockpit activities, such as failure to initiate activities at the appropriate time, misprioritization of activities, or the failure to appropriately monitor activities and terminate them when required. To facilitate the management of the cockpit activities, a computational aid, the Agenda Manager (AM) has been developed for use in simulated cockpit environments in an investigation which was one aspect of a more extensive research project supported by the NASA Ames Research Center. The AM is directed at the management of goals and functions, the actors who perform those functions, and the resources used by these actors. Development of an earlier AM version, the Cockpit Task Management System (CTMS), demonstrated that it could be used to assist flightcrews in the improvement of cockpit activity management under experimental conditions, assuming that the AM determined pilot goals accurately as well as the functions performed to achieve those goals. To overcome AM limitations based on that assumption, a pilot goal communication method (GCM) was developed to facilitate accurate recognition of pilot goals. Embedded within AM, the GCM was used to recognize pilot goals and to declare them to the AM. Two approaches to the recognition of pilots goals were considered: (1) The use of an Automatic Speech Recognition (ASR) system to recognize overtly or explicitly declared pilot goals, and (2) inference of covertly or implicitly declared pilot goals via use of an intent inferencing mechanism. These two methods were integrated into the AM to provide a rich environment for the study of human-machine interactions in the supervisory control of complex dynamic systems. Through simulated flight environment experimentation, the proposed GCM has demonstrated its capability to accurately recognize pilot goals and to handle incorrectly declared goals, and was validated in terms of subjective workload and pilot flight control performance. / Graduation date: 1997

The flightcrew of a modern airliner operates in a multi-tasking environment with several tasks competing for the same attentional resources at the same time. Too many tasks vying for the crew's attention concurrently imposes a heavy workload on the flightcrew. This results in the satisfactory execution of some tasks at the expense of others. Consequently, flightcrews must manage cockpit tasks a process we call Cockpit Task Management (CTM). Funk (1991) defines cockpit task management (CTM) as the process flightcrews use to prioritize cockpit tasks, allocate required resources, initiate and terminate multiple concurrent tasks. Despite improvements in aircraft reliability and advancements in aircraft cockpit automation, "pilot error" is cited as the main reason (over 60% of all aircraft accidents) for planes still falling out of the skies. One of the objectives of this research was to determine the significance of CTM errors in "pilot errors". Having established its significance, the next step was to refine the existing error taxonomy of Chou & Funk (1991). A structured error classification methodology was also developed for classifying CTM errors and validated using 470 Aviation safety Reporting System (ASRS) airline incident reports. This study identified CTM errors as a significant component of "pilot errors" accounting for 231 of the 470 incidents analyzed (49.2%). While Task Initiation errors accounted for the largest of the general error categories (41.5%), it was the Task Prioritization errors (35% of general and specific error categories) that unlocked the door that led to error committals in the other error categories. Task Prioritization errors led to Resource allocation errors which, in turn, resulted in several kinds of errors being committed in the other categories. The findings had implications that were largely training-based. In particular, the importance of pilot education which CTM provides (as opposed to crew training that CRM provides) is emphasized. The incorporation of formal CTM concept into existing CRM training programs was advocated. In addition, a staggered scheduling mechanism in crew training agenda involving CTM, CRM, Line-Oriented-Flight-Training (LOFT) and simulator sessions was suggested. A recommendation was made for a comprehensive Cockpit Task Management System (CTMS) to be installed in the cockpit to help crews to prioritize tasks and remind them of the need to initiate, terminate or reprioritize tasks as necessary. The inclusion of Air Traffic Control personnel in flightcrew training sessions was also recommended. / Graduation date: 1994

No description available.

Thesis (Ph.D. (Physics)) -- University of Limpopo, 2021 / Titanium metal and its alloy components find extensive applications in various industries such as aerospace, medicine and automotive due to its light weight-strength ratio. More importantly, titanium-based components with better surface finishing are required in the titanium manufacturing industries. However, these components suffer from surface roughness and brittleness due to the formation of alpha-case layer. Recently, the etching process has been widely used for metal surface modification, but the etching mechanism and the choice of etchant are not well prescribed. On the other hand, the adsorption of halogen molecules on the metal surface has received much attention due to their technological applications and relevance for material surface processing, corrosion and etching. This is considered as a promising approach towards selecting an effective etchant for the metal surface etching process. In this study, the first-principle approach has been used to study the adsorption behaviour of halogen molecules and ions on Ti (100) and (110) surfaces. Their adsorption mechanism was deduced from the calculated adsorption energy, heats of formation, desorption energy, work function, charge density difference and density of states. In particular, to understand how different etchant can influence the properties of titanium metal surface during etching process. Firstly, the free halogen molecules (HF, HCl, HBr and HI), as well as the clean Ti (100) and (110) surfaces were investigated to deduce the reactivity and surface stability, respectively. It was established that the HF dissociate easily due to its lowest dissociation energy and higher electronegativity, which suggest stronger interaction with the Ti surfaces. The halogen molecules stability trend was found to follow the order of HF>HCl>HBr>HI consistent with the electronegativity strength. Furthermore, it was also found that Ti (110) is the most stable surface displaying the lowest surface energy as compared to Ti (100) surface. v Secondly, the adsorption of halogen molecules on Ti (100) and Ti (110) surfaces was studied to investigate the chemical interaction and their reactivity. The halogens were adsorbed on three possible adsorption sites (Top, Bridge and Hollow) and their reaction is spontaneous. Moreover, the bridge and top sites were found to be the most favourable sites on Ti (100) and Ti (110) surfaces, respectively. Our results showed that all halogen molecules dissociate spontaneously on both Ti surfaces. The findings revealed that the adsorption of halogen molecules on Ti surfaces is energetically favourable suggesting adsorption energy strength order of 𝐸𝑎𝑑𝑠𝐻𝐹>𝐸𝑎𝑑𝑠𝐻𝐶𝑙>𝐸𝑎𝑑𝑠𝐻𝐵𝑟>𝐸𝑎𝑑𝑠𝐻𝐼. This indicates that the adsorption of HF molecule on these surfaces is thermodynamically more stable than HCl, HBr and HI molecules. Also, our results revealed that the adsorption of halogen ions (F-, Cl-, Br- and I-) is more favourable than the adsorption of halogen molecules (HF, HCl, HBr and I) on the bridge site in both Ti surfaces considered. The F ion was found to be the most preferable than Cl, Br, and I ions. In addition, the interaction of halogen ions with Ti surfaces was deduced with regards to electron charge. We found that the amount of electron charge transferred depends on the adsorption energy strength. In particular, it was found that the F atom accepts more electrons than other halogen ions. Moreover, the spherical shape was observed, this suggests that the charge density distribution between Ti atom and halogen exhibit ionic bonding behaviour. We also found that the adsorption of halogen has a stronger effect on the work function of Ti surfaces depending on the halogen ion. The magnitude of the induced work function varies from the halogen ionic order of F>Cl>Br>I. Lastly, in order to describe the dependence of the surface coverage of an adsorbed molecule, F2 and Cl2 molecules were adsorbed on Ti (100) surface at different coverages. We observed the formation of etching products TixFy and TixCly species on the surface. The heats of formation (EHF) and desorption energy of volatile etch products were calculated. Our findings show that the formed volatile molecules (TixFy and TixCly) are energetically favourable (EHF<0), suggesting an vi exothermic process. We also found that the TixFy clusters is more stable with lower heats of formation than the TixCly species. Moreover, the desorption energy of the formed volatile (TiF4) species was found to be lower than TiCl4 indicating that that TiF4 species desorb easily. This demonstrates that F2 is more suitable for surface etching as compared to Cl2. / Council for Scientific and Industrial Research (CSIR) and the Department of Science and Innovation (DSI)