## 4 Discussion  
In this study, we investigated the impact of expertise on aircraft maintenance activity. The key findings of our study can be summarized as follows: Our indicators on activity duration are consistent with the body of literature on the subject [19; 26; 27; 28; 29; 77; 78]. Experts have a lower task completion time than novices (H1). The maintenance task encompasses the execution of motor actions that are prescribed by the procedural instructions outlined in the aircraft maintenance manual. Experts are faster on both sides of the task (execution duration and document consultation). Differences between novices and experts are more important in the time dedicated to procedural information intake. On average, novices took 35.9% longer to execute the task and 71.6% longer to consult the documentation. All participants consulted the procedural document, regardless of the level of expertise of the participants, with frequent back-and-forth between the documentation consultation activity and execution throughout the task. These results are consistent with the context of the maintenance task, particularly with the safety aspect inherent in the aviation field, but also with the complexity of the procedures [34] necessary for the maintenance of a helicopter, which makes it impossible to fully memorize it [50]. Expertise has a global effect on all tasks of the maintenance activity, but its effect on document consultation is more complex. Concerning the NASA-TLX dimensions, novices showed a significantly higher score on both the effort and the mental workload (H3) dimensions as compared to experts. These findings can be explained by considering the influence of the knowledge and skills of the experts on the efficiency of the maintenance activities: both in the extraction of crucial information relative to the current task stage and in the planning of the execution based on the information derived from the procedural document. Our study shows that even if the maintenance activity generates physical constraints (displacement, awkward postures, load  
Figure 6: Box plots comparing per step and per expertise group (**A**) the average consultation time, and (**B**) the number of consultations. bearing) [9; 70; 72; 79], the use of procedures requires a strong mobilization of attentional and cognitive resources, corroborating the findings of [45; 50; 80; 81; 82]. Moreover, our results show that the amount of procedural information intake is not linear during the task. During the removal phase, operators, regardless of their level of expertise, place a greater emphasis on procedural information intake, particularly during the first step of removal for novices and the first and second steps for experts. Removal is theoretically less complicated than installation [83]. Access to certain parts may remain restricted during the removal phase until other components have been deposited. These accessibility constraints are inherent in the system and embody the interdependent relationships that structure the instructions within the procedure. They provide additional information by clarifying the sequence of actions to be followed by the technician. We suggest that the longer duration and greater importance of information gathering at the beginning of a task are not solely related to the execution of instructions during those intervals, but rather to the overall planning of the maintenance task. In this study, procedural information intake would serve two purposes, an execution purpose throughout the task and a general planning purpose at the beginning of the task. The data relating to the number of consultations and average consultation duration illustrates the phenomenon of atomization in the maintenance task. The aircraft maintenance activity observed for all participants shows a phenomenon observed in the context of other tasks involving a procedural document in other domains [37; 40; 51]. The whole consultation duration of the document is segmented into multiple short consultations.