## 1 Introduction
### Reaction to Unexpected Events  
Research has examined pilot reactions to unexpected events, specifically focusing on startle and surprise on the flight deck [6; 7]. In recent years, the prevalence of flight deck automation surprises caused by unexpected events and mode confusions has been investigated. When faced with surprising and startling events such as technical malfunctions or automation surprises, pilots' performance can be significantly impaired, and the likelihood of negative outcomes following unexpected events increases [8; 9; 10; 11]. Adverse manifestations of pilot responses to unexpected events may be longer reaction times, greater increases in heart rate and pupil dilation, reduced eye movement scanning, higher workload, or other examples of poorer performance [11; 12; 13].  
The performance issues in unexpected situations can often be traced back to insufficient adaptation of one's frame to the situation [11]. Studies on automation system failures in vehicle autonomous driving have found that a better understanding of the limitations of driving automation is associated with faster responses. When drivers can anticipate failures, they are more prompt in taking control [14].  
Automation may fail as a result of known system limits (system-limit failure) or of malfunctions that are unforeseen by system designers (system-malfunction failure) [15]. The failures caused by known limits in automation systems can be mitigated through training, enabling operators to anticipate them. However, there are certain failures that even the system designers themselves cannot foresee, making it impractical to address them through training.  
From the perspective of pilots, for system-limit failures, they are aware of the known system limitations and potential failures. They can anticipate and respond to these failures based on their understanding of the automation system, environmental cues, and self-knowledge. However, for system-malfunction failures that even the designers cannot foresee, pilots cannot rely on pre-established accurate cues or self-knowledge to anticipate and prepare for them. It is worth mentioning that some failures, although anticipated by automation system designers, may not be adequately addressed in pilot training due to various reasons. If pilots lack experience and knowledge in dealing with such failures, they may find themselves in a situation similar to facing system-malfunction failures, wherein they are unable to anticipate and prepare in advance. Therefore, from the perspective of pilots, their ability to anticipate and prepare for failures can serve as a key indicator for distinguishing between system-limit failures and system-malfunction failures, which may be more easily understood from the pilot's viewpoint.  
Despite numerous studies conducted on pilot reactions to aircraft automation system failures, over the years, there has been a lack of distinction between system-limit failures and system-malfunction failures, resulting in a partial understanding of performance in responding to these failures. Therefore, there is a need to differentiate between automation system failure types from the perspective of pilots and conduct research on their reactions.