###### Abstract  
Air route alternation caused by unexpected events in abnormal or emergency situations often produces adverse consequences on an operator's cognition and behavior in flight tasks. Under such a circumstance, it is especially necessary to examine the utility of the interaction displays usually designed based on the routine environment. This study was aimed to investigate the effects of air route alternation and display design on operators' situation awareness (SA), task performance and mental workload during simulated flight tasks. Twenty-four participants attended an experiment where they were instructed to perform simulated flight tasks with three types of display designs in both air-route-as-planned and air-route-altered conditions. Subjective measures, behavioral measures and eye movement measures were adopted to assess the participants' SA, task performance and mental workload. The results show that unexpected air route alternation increases mental workload as well as deteriorates the SA and task performance due to the gap between attention resource demand and supply. Reducing the demand of the operator's attention resource should be the focus when coping with unexpected events in abnormal situations. In addition, reasonable information layout, such as a center-layout design of the critical decision-making information, is more important than information salience for improving the SA and task performance in abnormal situations. Nevertheless, indicators with a high-salience design, such as a more open window design and immersive design, are still worth recommending. air route alternation; display design; situation awareness; task performance; mental workload; abnormal situation; unexpected events; aviation safety +
Footnote †: journal: Medicalwhere operators are required to respond immediately and appropriately to unexpected events or emergencies. In these scenarios, demands on the operators' SA can be even higher so that the operators' mental resources may not be able to provide sufficient support for good task performance, thereby leading to human errors [13; 14; 15; 16]. There is a growing interest in examining the influence of unexpected events or emergencies in abnormal situations on operators' SA and other activities in the aviation and transportation fields. The literature has pointed out that operators do not always make appropriate responses to the unexpected events, such as air route alternation caused by in-flight engine malfunction, air traffic disruption and in-flight medical emergencies, leading to a deterioration in system safety and reliability [17; 18; 19; 20; 21]. Different from routine working situations, workflows in abnormal situations would be interrupted or disrupted by unexpected events, and operators have to make a quick decision on whether to keep on the current workflows or perform an alternative one to address the unexpected events [21; 22; 23]. For example, when an in-flight medical emergency arises, pilots in cockpits need not only to seek medical support but also to cooperate with ground crews to evaluate the possibility of re-planning the air route. During this process, adequate SA is required for quick assessment, otherwise it may lead to delayed or risky decisions [24; 25]. [PERSON] et al. suggested that when a sudden emergency occurs, pilots need to formulate an appropriate list of alternative actions to handle the suspension or termination of the original flight plan, and it is necessary to support the pilot's situation assessment and decision making with planning aids [10; 15; 16]. Overall, the operators' SA tends to decline in workflows with unexpected changes, which probably lead to performance deterioration and even human errors [16; 26]. Therefore, importance has been attached to decreasing the mental demands to maintain the operator's SA in abnormal situations [18; 19; 20]. A good interaction display design (i.e., what information to present and how to present the information) is also conducive to maintaining operators' SA [27; 28; 29].