<p>The purpose of this study is to find out if the Swedish Air Force and the military aviation industry, Saab Aerosystems, use an HTO perspective in incident investigations. The research objectives are to explore existing organizational and accident models, analyze the reporting system using the models, and suggest possible improvements to the existing incident investigation system. Fishman’s (1999) model for pragmatic studies was used to describe the study’s theoretical approach. Triangulation by literary review, case study and interviews were used to ensure validity and reliability.</p><p>Three models were chosen: Rollenhagen’s HTO model (1997), Leveson’s STAMP (2002), and Shappell and Wiegmann’s HFACS (2000). The models were further tested in the case study, revealing that their usefulness depends on type of incident, and that they leave a lot up to the investigator.</p><p>Interviews were conducted with key individuals at Saab Aerosystems as well as at the Swedish Armed Forces’ Headquarters. The interviews showed that the incident reporting system in question is a well functioning one, mainly due to the blame-free culture, multidisciplinary investigative teams, good feedback and a generally good knowledge of the HTO concept. Difficulties within the organizations exist due to organizational boundaries between the manufacturer and the operator, and recurring structural reorganizations within the Swedish Armed Forces. Saab acknowledges the emphasis on technical issues. The Flight Safety department at the headquarters is currently working with implementing HFACS into the Flight Safety Database.</p><p>Our recommendations for Saab Aerosystems and the Air Force include:</p><p>For Saab Aerosystems:</p><ul><li>Evaluate and learn from existing HTO work within the organization, and incorporate the results into existing processes and instructions for incident investigations.</li><li>Make use of the theoretical models, where applicable, in the processes as well.</li><li>Focus on HFACS in order to synchronize with the Air Force.</li><li>Consider employing an HTO specialist.</li></ul><p>For the Air Force:</p><ul><li>Consider influences from other HTO models, like Rollenhagen’s or Leveson’s models, while still in the development phase of implementing HFACS.</li><li>Perform risk analyses regarding the effects on flight safety when doing reorganizations.</li></ul><p>For both Saab Aerosystems and the Air Force we recommend:</p><p>Use Leveson’s model STAMP for complex and serious incidents, comprising of organizational, human and technical aspects.</p> / <p>Denna studie har som syfte att ta reda på om det svenska Flygvapnet och den militära flygindustrin, Saab Aerosystems, använder ett MTO-perspektiv vid incidentutredningar. Forskningsmålen är att utforska befintliga organisations- och olycksmodeller, att analysera rapporteringssystemet med hjälp av modellerna, samt att föreslå möjliga förbättringar på det existerande incidentrapporterings- och utredningssystemet. Fishmans (1999) modell för pragmatiska studier användes som teoretisk utgångspunkt. För att säkerställa validitet och reliabilitet användes triangulering, bestående av litteraturstudie, fallstudie, samt intervjuer.</p><p>Tre modeller valdes ut: Rollenhagens MTO-modell (1997), Levesons STAMP (2002) och Shappell och Wiegmanns HFACS (2000). Modellerna användes i fallstudien, med resultatet att modellernas användbarhet bedömdes variera beroende på typ av incident, samt att de lämnar mycket åt utredarens erfarenhet.</p><p>Intervjuer genomfördes med nyckelpersoner på Saab Aerosystems och på Försvarsmaktens Högkvarter. Intervjuerna visade att rapporteringssystemet i fråga är väl fungerande, främst tack vare rapporteringskulturen, de multidisciplinära utredningsgrupperna, god återkoppling och en generellt sett god kännedom om MTO-konceptet. Organisatoriska svårigheter är dels gränsdragningen mellan tillverkare och användare, dels återkommande omstruktureringar inom Försvarsmakten. Saab medger också att deras fokus ligger främst på det tekniska. Flygsäkerhetsavdelningen på Högkvarteret arbetar med att införa HFACS i flyg­säker­hetsdatabasen.</p><p>Våra rekommendationer till Saab Aerosystems och till Flygvapnet inkluderar:</p><p>Till Saab Aerosystems:</p><ul><li>Utvärdera och drag lärdom av befintligt MTO-arbete inom organisationen, inkludera dessa resultat i befintliga processer och instruktioner för incidentutredningar.</li><li>Utnyttja fler teoretiska modeller i processen, där så är lämpligt.</li><li>Fokusera på HFACS för att synkronisera med Flygvapnet. <ul><li>Fundera på att anställa en MTO-specialist.</li></ul></li></ul><p>Till Flygvapnet:</p><ul><li>Fundera på att också införa delar av andra MTO-modeller, som Rollenhagens eller Levesons modeller, under implementeringsfasen av HFACS. </li><li>Genomför riskanalyser av påverkan på flygsäkerhet vid omorganisationer.</li></ul><p>Till både Saab Aerosystems och Flygvapnet rekommenderar vi:</p><p>använd Levesons modell STAMP vid mer komplexa och allvarliga incidenter som innefattar organisatoriska, mänskliga och tekniska aspekter.</p>

<p>The Swedish Aviation Safety Authority has decided to standardise a classification system for reporting deviations found in inspections. The purpose of a classification system is that similar deviations always should be reported in the same way since this will enable better decisions regarding different risk areas. The inspectors are therefore constrained to use a standardised classification system and are not free to use their own words when reporting deviations. A hierarchal classification system with predefined phrases is in aviation referred to as taxonomy. Taxonomy is already in use when reporting accidents and incidents but not when reporting deviations found in inspections. If the taxonomy also could be implemented when reporting deviations found in inspections it would make it possible to find out what kind of accident or incident the deviation has been involved in. To make this connection possible and to enable further analyses the information has to be stored, preferably in a database. </p><p>We have examined the already existing taxonomy and its usability in inspection reporting. Were the old taxonomy has been found insufficient we have examined how to build up a new suitable taxonomy. We have also begun the extension of the taxonomy in certain domains in aviation. To be able to test the extended taxonomy we have developed a system support that consists of a database and help functions consisting of checklists and linked regulation text. The system support also contains risk assessment matrixes. </p><p>We have through this work seen that a great extension of the existing taxonomy is necessary. As the taxonomy is formed it is hard to make direct connections between accidents/incidents and deviations found in inspections without a mapping tool. However we think that a database management system should be implemented in inspections. A database management system would be a useful help for the inspectors and enable easier access to data for analyses.</p>

The purpose of this study is to find out if the Swedish Air Force and the military aviation industry, Saab Aerosystems, use an HTO perspective in incident investigations. The research objectives are to explore existing organizational and accident models, analyze the reporting system using the models, and suggest possible improvements to the existing incident investigation system. Fishman’s (1999) model for pragmatic studies was used to describe the study’s theoretical approach. Triangulation by literary review, case study and interviews were used to ensure validity and reliability. Three models were chosen: Rollenhagen’s HTO model (1997), Leveson’s STAMP (2002), and Shappell and Wiegmann’s HFACS (2000). The models were further tested in the case study, revealing that their usefulness depends on type of incident, and that they leave a lot up to the investigator. Interviews were conducted with key individuals at Saab Aerosystems as well as at the Swedish Armed Forces’ Headquarters. The interviews showed that the incident reporting system in question is a well functioning one, mainly due to the blame-free culture, multidisciplinary investigative teams, good feedback and a generally good knowledge of the HTO concept. Difficulties within the organizations exist due to organizational boundaries between the manufacturer and the operator, and recurring structural reorganizations within the Swedish Armed Forces. Saab acknowledges the emphasis on technical issues. The Flight Safety department at the headquarters is currently working with implementing HFACS into the Flight Safety Database. Our recommendations for Saab Aerosystems and the Air Force include: For Saab Aerosystems: Evaluate and learn from existing HTO work within the organization, and incorporate the results into existing processes and instructions for incident investigations. Make use of the theoretical models, where applicable, in the processes as well. Focus on HFACS in order to synchronize with the Air Force. Consider employing an HTO specialist. For the Air Force: Consider influences from other HTO models, like Rollenhagen’s or Leveson’s models, while still in the development phase of implementing HFACS. Perform risk analyses regarding the effects on flight safety when doing reorganizations. For both Saab Aerosystems and the Air Force we recommend: Use Leveson’s model STAMP for complex and serious incidents, comprising of organizational, human and technical aspects. / Denna studie har som syfte att ta reda på om det svenska Flygvapnet och den militära flygindustrin, Saab Aerosystems, använder ett MTO-perspektiv vid incidentutredningar. Forskningsmålen är att utforska befintliga organisations- och olycksmodeller, att analysera rapporteringssystemet med hjälp av modellerna, samt att föreslå möjliga förbättringar på det existerande incidentrapporterings- och utredningssystemet. Fishmans (1999) modell för pragmatiska studier användes som teoretisk utgångspunkt. För att säkerställa validitet och reliabilitet användes triangulering, bestående av litteraturstudie, fallstudie, samt intervjuer. Tre modeller valdes ut: Rollenhagens MTO-modell (1997), Levesons STAMP (2002) och Shappell och Wiegmanns HFACS (2000). Modellerna användes i fallstudien, med resultatet att modellernas användbarhet bedömdes variera beroende på typ av incident, samt att de lämnar mycket åt utredarens erfarenhet. Intervjuer genomfördes med nyckelpersoner på Saab Aerosystems och på Försvarsmaktens Högkvarter. Intervjuerna visade att rapporteringssystemet i fråga är väl fungerande, främst tack vare rapporteringskulturen, de multidisciplinära utredningsgrupperna, god återkoppling och en generellt sett god kännedom om MTO-konceptet. Organisatoriska svårigheter är dels gränsdragningen mellan tillverkare och användare, dels återkommande omstruktureringar inom Försvarsmakten. Saab medger också att deras fokus ligger främst på det tekniska. Flygsäkerhetsavdelningen på Högkvarteret arbetar med att införa HFACS i flyg­säker­hetsdatabasen. Våra rekommendationer till Saab Aerosystems och till Flygvapnet inkluderar: Till Saab Aerosystems: Utvärdera och drag lärdom av befintligt MTO-arbete inom organisationen, inkludera dessa resultat i befintliga processer och instruktioner för incidentutredningar. Utnyttja fler teoretiska modeller i processen, där så är lämpligt. Fokusera på HFACS för att synkronisera med Flygvapnet. Fundera på att anställa en MTO-specialist. Till Flygvapnet: Fundera på att också införa delar av andra MTO-modeller, som Rollenhagens eller Levesons modeller, under implementeringsfasen av HFACS. Genomför riskanalyser av påverkan på flygsäkerhet vid omorganisationer. Till både Saab Aerosystems och Flygvapnet rekommenderar vi: använd Levesons modell STAMP vid mer komplexa och allvarliga incidenter som innefattar organisatoriska, mänskliga och tekniska aspekter.

The Swedish Aviation Safety Authority has decided to standardise a classification system for reporting deviations found in inspections. The purpose of a classification system is that similar deviations always should be reported in the same way since this will enable better decisions regarding different risk areas. The inspectors are therefore constrained to use a standardised classification system and are not free to use their own words when reporting deviations. A hierarchal classification system with predefined phrases is in aviation referred to as taxonomy. Taxonomy is already in use when reporting accidents and incidents but not when reporting deviations found in inspections. If the taxonomy also could be implemented when reporting deviations found in inspections it would make it possible to find out what kind of accident or incident the deviation has been involved in. To make this connection possible and to enable further analyses the information has to be stored, preferably in a database. We have examined the already existing taxonomy and its usability in inspection reporting. Were the old taxonomy has been found insufficient we have examined how to build up a new suitable taxonomy. We have also begun the extension of the taxonomy in certain domains in aviation. To be able to test the extended taxonomy we have developed a system support that consists of a database and help functions consisting of checklists and linked regulation text. The system support also contains risk assessment matrixes. We have through this work seen that a great extension of the existing taxonomy is necessary. As the taxonomy is formed it is hard to make direct connections between accidents/incidents and deviations found in inspections without a mapping tool. However we think that a database management system should be implemented in inspections. A database management system would be a useful help for the inspectors and enable easier access to data for analyses.

This project examines the safety management of civil aircraft accident investigation authorities in International Civil Aviation Organization (ICAO) Member States, with particular emphasis on the independence of the investigations. The research aims to establish the current level of resources and methodology adopted by Member States’ accident investigation authorities. The output of this work not only identifies the current situation but informs initiatives for some of the States in the process of establishing their investigation capability. ICAO Annex 13 was analysed and found to be based on the principle of independent accident investigations. Also, a four dimensional measuring index (4DMI) has been developed to measure the independence of accident investigations in ICAO Member States. Data were collected from 45 States and are presented in the thesis. As a result of applying the 4DMI to the collected data, the States were ranked according to their scores, and divided into four categories of independence. Analysis of the four categories and the scores from the four dimensions revealed that States approach the concept of investigation independence in different ways; however, there are several practices that are common within the highest independence category and several other practices that are common within the lowest independence category. The research recommends that States should work towards improving their overall investigation independence by implementing the seven identified practices in the High-Independence category and distance themselves from the five practices identified as common in the Low-Independence category.

There are many pieces of flight deck research on general use of written English language technical information and problem solving using technical documentation. Contributory causes of aircraft accidents have been due to misunderstandings of crew alerts and procedural divergence by English as-a-second language flight crewmembers (ESL). Research was conducted to understand impact of written English language technical information on ESL flight crewmembers’ performance. Two types of systems were evaluated, technical documentation and crew alerting systems that contain technical information, with respect to their impact on ESL flight crewmember performance. Preliminary analysis results indicated written English language technical information can be confusing, difficult to read and interpret, and leads to misunderstandings by ESL flight crewmembers during aircraft nonnormal conditions. English as-a-second language flight crewmembers indicated they often experience problems executing written English language technical procedures after outset of crew alerts. Conversely, experimental trials revealed ESL flight crewmembers did not experience many cognitive performance issues with use of crew alerting systems and technical information designed with an English language emphasis. English as-a second language flight crewmembers’ English language proficiency, background knowledge, and use of use of metacognitive strategies to read and comprehend written English language on crew alerting and information systems, indicated they utilized written English technical information with ease. Particularly, ESL flight crewmembers’ workload was low, they had fast response times to system faults, and they experienced minimal procedural deviations. On the contrary, when ESL flight crewmembers utilized written English language technical procedures translated into their native language during non-normal conditions, they experienced several cognitive performance challenges. English as-a second language flight crewmembers’ background knowledge of written English language technical information translated into their native language, use of metacognitive strategies to read and comprehend written English language translated into their native language, indicated they experienced difficulties with reading and comprehending translated technical information on information systems. Particularly, ESL flight crewmembers were challenged cognitively when they responded to crew alerts through execution of decision-making processes. They indicated translation of written English language technical information into their native language was a pre-cursor to procedural deviation, long response times to system issues, as well as high workload during experimental trials. It is recommended that further research focus on design and use of written English language technical documentation by ESL flight crewmembers during non-normal conditions. It is also recommended that if deemed practical by the aviation industry, further research should focus on design, integration, and utilization of technical documentation in a language(s) other than English, and measurement of ESL flight crewmembers performance on the flight deck.

A Engenharia de Resiliência (ER) é um novo paradigma para gestão da segurança o qual, apesar de possuir uma fraca estrutura teórica, vem sendo aplicado em diversos setores. Neste contexto, este trabalho tem como objetivo a identificação de fontes de fragilidade e resiliência em empresas de táxi aéreo. Para essa identificação foram utilizados os seguintes princípios da ER: flexibilidade, consciência, aprendizagem e comprometimento da alta direção. O estudo de caso foi à estratégia de pesquisa adotada, tendo sido investigadas duas empresas de táxi aéreo de pequeno porte. O método de pesquisa envolveu as seguintes etapas: (a) caracterização da empresa sob a perspectiva de três subsistemas que compõem seu sistema sócio-técnico (social, técnico e organização do trabalho); (b) identificação dos constrangimentos e adaptações dos funcionários no desempenho de suas atividades; (c) identificação das fontes de fragilidade e resiliência a partir dos 4 princípios da ER, desdobradas em evidências empíricas conforme a literatura Os resultados mostram que 11 fontes estavam relacionadas à fragilidade da empresa A e 6 da empresa B. Da mesma forma, identificou-se 9 fontes de resiliência na empresa A e na empresa A. Em particular, o objetivo primário da empresa (lucro, no caso de uma das empresas; servir aos proprietários, no caso da outra empresa) revelou-se como uma fonte comum a todas as fontes de resiliência ou fragilidade e quase todas as fontes de resiliência constituíram de ações isoladas dos operadores, revelando a emergência dessas fontes na organização informal das empresas. / Resilience Engineering (RE) is a new safety management paradigm which, in spit of its weak theoretical structure, has been applied in many domains. In this context, this research has a main objective of identifying sources of brittleness and resilience on air taxi carriers. To accomplish this objective, this work used as base the following RE principles: flexibility, conscious, learning, top management commitment. Case study was the research strategy used, which investigated two small air taxi carriers. Research method involved the following steps: (a) air taxi carrier characterization from the tree subsystems that compose socio-technical system (social, technical, work system); (b) employees constraints and adaptations identification during the job; (c) brittleness and resilience source identification from 4 RE principles, unfolded in empirical evidences according to literature. The results show that 11 sources were related to brittleness at company A and 6 at company B. At the same way, 9 sources of resilience were identified at company A and company B. In particular, the main air taxi carrier objective (to profit, in of one them; to serve, to another one) appeared as a common to all sources of brittleness and resiliencies and almost all sources of resilience were constituted of isolated action from operators, revealing resilience source emergence from companies informal organization.

A Engenharia de Resiliência (ER) é um novo paradigma para gestão da segurança o qual, apesar de possuir uma fraca estrutura teórica, vem sendo aplicado em diversos setores. Neste contexto, este trabalho tem como objetivo a identificação de fontes de fragilidade e resiliência em empresas de táxi aéreo. Para essa identificação foram utilizados os seguintes princípios da ER: flexibilidade, consciência, aprendizagem e comprometimento da alta direção. O estudo de caso foi à estratégia de pesquisa adotada, tendo sido investigadas duas empresas de táxi aéreo de pequeno porte. O método de pesquisa envolveu as seguintes etapas: (a) caracterização da empresa sob a perspectiva de três subsistemas que compõem seu sistema sócio-técnico (social, técnico e organização do trabalho); (b) identificação dos constrangimentos e adaptações dos funcionários no desempenho de suas atividades; (c) identificação das fontes de fragilidade e resiliência a partir dos 4 princípios da ER, desdobradas em evidências empíricas conforme a literatura Os resultados mostram que 11 fontes estavam relacionadas à fragilidade da empresa A e 6 da empresa B. Da mesma forma, identificou-se 9 fontes de resiliência na empresa A e na empresa A. Em particular, o objetivo primário da empresa (lucro, no caso de uma das empresas; servir aos proprietários, no caso da outra empresa) revelou-se como uma fonte comum a todas as fontes de resiliência ou fragilidade e quase todas as fontes de resiliência constituíram de ações isoladas dos operadores, revelando a emergência dessas fontes na organização informal das empresas. / Resilience Engineering (RE) is a new safety management paradigm which, in spit of its weak theoretical structure, has been applied in many domains. In this context, this research has a main objective of identifying sources of brittleness and resilience on air taxi carriers. To accomplish this objective, this work used as base the following RE principles: flexibility, conscious, learning, top management commitment. Case study was the research strategy used, which investigated two small air taxi carriers. Research method involved the following steps: (a) air taxi carrier characterization from the tree subsystems that compose socio-technical system (social, technical, work system); (b) employees constraints and adaptations identification during the job; (c) brittleness and resilience source identification from 4 RE principles, unfolded in empirical evidences according to literature. The results show that 11 sources were related to brittleness at company A and 6 at company B. At the same way, 9 sources of resilience were identified at company A and company B. In particular, the main air taxi carrier objective (to profit, in of one them; to serve, to another one) appeared as a common to all sources of brittleness and resiliencies and almost all sources of resilience were constituted of isolated action from operators, revealing resilience source emergence from companies informal organization.

A Engenharia de Resiliência (ER) é um novo paradigma para gestão da segurança o qual, apesar de possuir uma fraca estrutura teórica, vem sendo aplicado em diversos setores. Neste contexto, este trabalho tem como objetivo a identificação de fontes de fragilidade e resiliência em empresas de táxi aéreo. Para essa identificação foram utilizados os seguintes princípios da ER: flexibilidade, consciência, aprendizagem e comprometimento da alta direção. O estudo de caso foi à estratégia de pesquisa adotada, tendo sido investigadas duas empresas de táxi aéreo de pequeno porte. O método de pesquisa envolveu as seguintes etapas: (a) caracterização da empresa sob a perspectiva de três subsistemas que compõem seu sistema sócio-técnico (social, técnico e organização do trabalho); (b) identificação dos constrangimentos e adaptações dos funcionários no desempenho de suas atividades; (c) identificação das fontes de fragilidade e resiliência a partir dos 4 princípios da ER, desdobradas em evidências empíricas conforme a literatura Os resultados mostram que 11 fontes estavam relacionadas à fragilidade da empresa A e 6 da empresa B. Da mesma forma, identificou-se 9 fontes de resiliência na empresa A e na empresa A. Em particular, o objetivo primário da empresa (lucro, no caso de uma das empresas; servir aos proprietários, no caso da outra empresa) revelou-se como uma fonte comum a todas as fontes de resiliência ou fragilidade e quase todas as fontes de resiliência constituíram de ações isoladas dos operadores, revelando a emergência dessas fontes na organização informal das empresas. / Resilience Engineering (RE) is a new safety management paradigm which, in spit of its weak theoretical structure, has been applied in many domains. In this context, this research has a main objective of identifying sources of brittleness and resilience on air taxi carriers. To accomplish this objective, this work used as base the following RE principles: flexibility, conscious, learning, top management commitment. Case study was the research strategy used, which investigated two small air taxi carriers. Research method involved the following steps: (a) air taxi carrier characterization from the tree subsystems that compose socio-technical system (social, technical, work system); (b) employees constraints and adaptations identification during the job; (c) brittleness and resilience source identification from 4 RE principles, unfolded in empirical evidences according to literature. The results show that 11 sources were related to brittleness at company A and 6 at company B. At the same way, 9 sources of resilience were identified at company A and company B. In particular, the main air taxi carrier objective (to profit, in of one them; to serve, to another one) appeared as a common to all sources of brittleness and resiliencies and almost all sources of resilience were constituted of isolated action from operators, revealing resilience source emergence from companies informal organization.

Les exigences opérationnelles du métier de pilote sont susceptibles d'engendrer de la somnolence et des niveaux de charge mentale inadéquats (i.e., trop faible ou trop élevé) au cours des vols. Les dettes de sommeil et les perturbations circadiennes liées à divers facteurs (e.g., longues périodes de services, horaires de travail irrégulier, etc.) demandent aux pilotes de repousser sans cesse leurs limites biologiques. Par ailleurs, la charge de travail mental des pilotes présente de fortes variations au cours d'un vol : élevée au cours des phases critiques (i.e., décollage et atterrissage), elle devient très réduite pendant les phases de croisière. Lorsque la charge mentale devient trop élevée ou, à l'inverse, trop faible, les performances se dégradent et des erreurs de pilotage peuvent apparaître. La mise en oeuvre de méthodes de détection de l'état de somnolence et du niveau de charge mentale en temps quasi réel est un défi majeur pour le suivi et le contrôle de l'activité de pilotage. L'objectif de la thèse est de déterminer si la voix humaine peut permettre de détecter d'une part, l'état de somnolence et d'autre part, le niveau de charge mentale d'un individu. Dans une première étude, la voix de participants a été enregistrée lors d'une tâche de lecture avant et après une nuit de privation totale de sommeil (PTS). Les variations de l'état de somnolence consécutives à la PTS ont été évaluées au moyen de mesures auto-évaluatives et électrophysiologiques (ÉlectroEncéphaloGraphie [EEG] et Potentiels Évoqués [PEs]). Les résultats ont montré une variation significative après la PTS de plusieurs paramètres acoustiques liés : (a) à l'amplitude des impulsions glottiques (fréquence de modulation d'amplitude), (b) à la forme du signal acoustique (longueur euclidienne du signal et ses caractéristiques associées) et (c) au spectre du signal des voyelles (rapport harmonique sur bruit, fréquence du second formant, coefficient d'asymétrie, centre de gravité spectral, différences d'énergie, pente spectrale et coefficients cepstraux à échelle Mel). La plupart des caractéristiques spectrales ont montré une sensibilité différente à la privation de sommeil en fonction du type de voyelles. Des corrélations significatives ont été mises en évidence entre plusieurs paramètres acoustiques et plusieurs indicateurs objectifs (EEG et PEs) de l'état de somnolence. Dans une seconde étude, le signal vocal a été enregistré durant une tâche de rappel de listes de mots. La difficulté de la tâche était manipulée en faisant varier le nombre de mots dans chaque liste (i.e., entre un et sept, correspondant à sept conditions de charge mentale). Le diamètre pupillaire - qui est un indicateur objectif pertinent du niveau de charge mentale - a été mesuré simultanément avec l'enregistrement de la voix afin d'attester de la variation du niveau de charge mentale durant la tâche expérimentale. Les résultats ont montré que des paramètres acoustiques classiques (fréquence fondamentale et son écart type, shimmer, nombre de périodes et rapport harmonique sur bruit) et originaux (fréquence de modulation d'amplitude et variations à court-terme de la longueur euclidienne du signal) ont été particulièrement sensibles aux variations de la charge mentale. Les variations de ces paramètres acoustiques étaient corrélées à celles du diamètre pupillaire. L'ensemble des résultats suggère que les paramètres acoustiques de la voix humaine identifiés lors des expérimentations pourraient représenter des indicateurs pertinents pour la détection de l'état de somnolence et du niveau de charge mentale d'un individu. Les résultats ouvrent de nombreuses perspectives de recherche et d'applications dans le domaine de la sécurité des transports, notamment dans le secteur aéronautique. / Operational requirements of aircraft pilots may cause drowsiness and inadequate mental load levels (i.e., too low or too high) during flights. Sleep debts and circadian disruptions linked to various factors (e.g., long working periods, irregular work schedules, etc.) require pilots to challenge their biological limits. Moreover, pilots' mental workload exhibits strong fluctuations during flights: higher during critical phases (i.e., takeoff and landing), it becomes very low during cruising phases. When the mental load becomes too high or, conversely, too low, performance decreases and flight errors may manifest. Implementation of detection methods of drowsiness and mental load levels in near real time is a major challenge for monitoring and controlling flight activity. The aim of this thesis is therefore to determine if the human voice can serve to detect on one hand the drowsiness and on the other hand the mental load level of an individual. In a first study, the voice of participants was recorded during a reading task before and after a night of total sleep deprivation (TSD). Drowsiness variations linked to TSD were assessed using self-evaluative and electrophysiological measures (ElectroEncephaloGraphy [EEG] and Evoked Potentials [EPs]). Results showed significant variations after the TSD in many acoustic features related to: (a) the amplitude of the glottal pulses (amplitude modulation frequency), (b) the shape of the acoustic wave (Euclidean length of the signal and its associated features) and (3) the spectrum of the vowel signal (harmonic-to-noise ratio, second formant frequency, skewness, spectral center of gravity, energy differences, spectral tilt and Mel-frequency cepstral coefficients). Most spectral features showed different sensitivity to sleep deprivation depending on the vowel type. Significant correlations were found between several acoustic features and several objective indicators (EEG and PEs) of drowsiness. In a second study, voices were recorded during a task featuring word-list recall. The difficulty of the task was manipulated by varying the number of words in each list (i.e., between one and seven, corresponding to seven mental load conditions). Evoked pupillary response - known to be a useful proxy of mental load - was recorded simultaneously with speech to attest variations in mental load level during the experimental task. Results showed that classical features (fundamental frequency and its standard deviation, shimmer, number of periods and harmonic-to-noise ratio) and original features (amplitude modulation frequency and short-term variation in digital amplitude length) were particularly sensitive to variations in mental load. Variations in these acoustic features were correlated to those of the pupil size. Results suggest that the acoustic features of the human voice identified during these experiments could represent relevant indicators for the detection of drowsiness and mental load levels of an individual. Findings open up many research and applications perspectives in the field of transport safety, particularly in the aeronautical sector.