A Crew Workload Evaluation Methodology

In the NH90 programme, the operational efficiency is a permanent concern for the two versions. (the Tactical Transport and the Naval helicopters). The adequacy of the crew concept with the tasks and with the system characteristics has to be verified at each step of the development of the Man Machine Interface. For that, a stringent evaluation process of the crew workload, involving operational crews from the users, has been defined. In particular, each stage of the MMI design is evaluated by these crews, in real-time simulation with men in the loop. A methodology which does not interfere with the highly demanding tasks of the crew, in term of mental effort and stress, has been defined to evaluate the workload. Self-evaluations, by means of questionnaires filled in by the crew during the debriefing, correlated with physiological measurements (heart rate) are used. The use of self-evaluation method leads to subjective results. This is made more difficult by the context of the NH90 programme, which involves four nations ; all the operational crews have to fill in questionnaires which are not written in their mother language, the explanations being also given in English. That the reason why fuzzy quantities are used to represent the evaluations of the components of the workload and also the performance criteria. By applying fuzzy quantities computation techniques, the workload of a crew member can be derived. Then, combination laws are defined to compute the workload of a crew and the corresponding criteria. These laws make compromises between the quantities they combine. So, after this fuzzy quantities combination process, two criteria are available : the workload level and the performance level. The decision, on the acceptance of the crew workload, is made reasoning on these two criteria. Four rules, plus two to take into account boundary cases, are stated on these fuzzy criteria, representing the knowledge we have to decide. The first results have shown the robustness of the combination laws and of the decision process, even with a reduce amount of subjective observations.