Abstract: In extraordinary situation, human behaviour holds the key to recover from extraordinary situation to ordinary situation safety and rapidly. In order to obtain suitable countermeasures, it is necessary to know the, cause of human behaviour in these situations to trace back situation before extraordinary situation. This is enables us to estimate human behaviour in these situations and to make countermeasure points clear. Therefore we have studied the relation between cause and effect before and after extraordinary situations. Human behaviour consists of plural realized functions to achieve specific aim. According to an aim, in handling a ship, these functions could be classified into 6 categories. On the basis of 6 categories, we could classify human behaviour in extraordinary situation into 3 patterns, and moreover, these 3 patterns agree with how much the operator achieves functions of Positioning and Lookout before extraordinary situation. Then, we utilized Fault Tree Analysis to think the rationality about it. From a point of view of phenomenon, one situation is the consequence phenomenon which the fundamental situations phenomena results in. It can be showed as the top phenomenon on the fault tree. Hence the change of situation can be showed as the process which fundamental phenomena grow up to the top phenomenon. To consider situation with Fault Tree Analysis can clarify important points, which depends on its structure. As estimation with the structural importance, we obtained that functions of Positioning and Lookout in ordinary situation is important on the fault tree. On this account, the achievement level of these functions causes to grow into unsuitable situation. In fact, insufficient Positioning and Lookout brings the unsafe position with other ships in surrounding area before the extraordinary situation. And after, in extraordinary situation, it also brings the unsuitable reaction toward extraordinary situation. Both situations depend on insufficient functions. Moreover, we could obtain that expansion of Fault Tree based on 4 steps, recognition / evaluation / decision / execution, can clarify the detail of process, and this process means functions should be done in order. From this study, necessary functions in ordinary situation were clarified. Even if the operator met the, extraordinary situation, to achieve necessary functions in ordinary situation would bring to achieve necessary functions in extraordinary situation as suitable countermeasures toward extraordinary situation.

　

 What kind of human behaviour in ordinary situation does cause unsuitable behaviour in extraordinary situation? To know the cause of human behaviour in extraordinary situations will clarify the necessary factors to recover from extraordinary situations to ordinary situations safety and rapidly as much as possible.

 To clarify the key to the safe navigation at any time on the cause of human behaviour would make it possible to recover from extraordinary situation in a short time as a result, even if the operator met the extraordinary situation. Moreover, to clarify the process from ordinary situations to worse situations is effective to cut off the chain of unsuitable reaction.

 In this paper, we considered human behaviour on the unsafe navigation in extraordinary situation, especially about the situation before and after the rudder trouble in fairway. We utilized Fault Tree Analysis to trace the process up to unsafe situation.

　

2.1 Behaviour as an Function

　

 Behaviour consists of plural actions, and it can be regarded as a chain of actions. When the operators handle a ship, they have to achieve necessary functions for handling a ship by behaviour. So Behaviour as a function has its aim.

　

2.2 Behaviour Grouping into 6 Categories

　

 According to an aim, we classified every action into 6 categories in table 1.

 6 categories are, Positioning, Lookout, Planning, Maneuvering, Communication, and Extraordinary Reaction. Positioning is an action to gather information and decide the own position, Lookout is an action to gather information about the situation of surrounding area, Planning is an action to make and decide a maneuvering plan, Maneuvering is an action to handle the rudder and engine, Communication is an action to exchange information and instruct the specific procedure, and Extraordinary Reaction is an action to react toward extraordinary situations [1]. These belong to the elemental techniques [2]. We utilized these 6 categories to analyze.

　

　

3.1 Change of phenomenon to achieve mission

　

 Situation is caused by a change of phenomena and itself is one of phenomena.

 When the operators handle, a ship, they have missions to achieve every moment. For instance, missions are to follow the planed course line, to avoid other ship going across the own ship, and so on. The operator has to achieve necessary functions to achieve missions. Fig.1 shows these relations between mission, function and phenomenon.

　

　

3.2 Construct Fault Tree

　

 Unless functions are achieved, the mission above functions would not be achieved. In other wards, if necessary functions below the mission achieved, the mission would be accomplished. When the mission is not achieved, to take one example of many cases, this situation can be explained by Fault Tree shown as Fig.3 using Fault Tree connection symbols shown as Fig.2. The top phenomenon is the incomplete mission.

　

　

 We can choose suitable connection symbols depending on conditions.

　

　

 Although we make Fault Tree about the same phenomenon, there are some kinds of Fault Tree structure. The structure of Fault Tree depends on its objective of research and its condition of system. The different view of point to research makes the different structure of Fault Tree. Therefore the specified view of point fixes the structure of Fault Tree.

　

3.3 Tracing the process growing up to incomplete mission in handling a ship on fault tree

　

3.3.1 6 Categories of actions on fault Tree

　

 When the operators handle a ship, they achieve some necessary functions from 6 categories of actions; Positioning, Lookout, Maneuvering, Communication, Planning, and Extraordinary Reaction; depending on the mission every situation.

 The operator has to evaluate situation suitably and to choose necessary functions, in due order, to achieve actions to achieve every function.

　

3.3.2 Process Tracing

　

 We can trace the process which each action under each function is growing up to incomplete mission on Fault Tree. This incomplete mission is an unsuitable situation. Therefore we can not obtain only the growing process but also the conditions to grow at the same time. This means that it is possible to trace a specific path among some growing processes.

　

4.1 Definition of Extraordinary Situation

　

 We defined an extraordinary situation as an unexpected situation in which system cannot carry out the original function by any matter.

　

4.2 Condition of Extraordinary Situation

　

 Fig.4 shows the extraordinary situation in this paper.

　

　

 The operator has to handle a ship to follow the fairway. When the own ship is changing direction to avoid the fishing boat with rudder, the rudder trouble happens. Shown as Fig.4, there are at least two ships to be kept a Lookout. The own ship is going by the fishing boat. One is going to the same direction from a few cables behind own ship. Moreover, the third one is coming from the opposite direction. These have potential collisions with own ship.

　

4.3 Behavior Patterns in Extraordinary Situation

　

 We obtained 3 behaviour patterns in extraordinary situations from 6 cases in simulator experiments which were carried out under the extraordinary situation shown Fig.4.

 Behaviour was evaluated by instructors. Suitable behaviour is evaluated with higher score. 6 cases were sampled at random, and arranged from case A with higher score to case F with lower score.

　

　

　

 In case A and case B with high score, when the operator carried out sufficient Positioning and Lookout before the trouble, reaction after the trouble is following.

 The operator carried out "Extraordinary Reaction" for instrument; for example to identify the trouble spot or to change to NFU (Non Follow up machinery) firstly. Then, he carried out "Maneuvering" to modify own position influenced by the trouble and to get rid of influences by the trouble. And next, after "Communication" to inform the trouble with surrounding ships, operation was returned to ordinary situation.

　

 In case C and case D with following score, when the operator carried out insufficient Positioning and Lookout before the trouble, reaction after the trouble is following.

 The operator carried out "Extraordinary Reaction" for instrument; for example to identify the trouble spot or to change to NFU firstly in the same way as case A and case B. Then, different from case A and case B, he carried out "Maneuvering" for speed reduction and "Communication" to inform the trouble with other ships having potential collision. And next, after "Extraordinary Reaction" to modify own position for removal of influences by the trouble, operation was returned to ordinary situation.

　

 In case E and case F with lower score, when the operator carried out more insufficient Positioning and Lookout before the trouble than case C and case D, reaction after the trouble is following.

 The operator carried out "Extraordinary Reaction" for instrument; for example to identify the trouble spot or to change to NFU firstly in the same way as case A from case D. Then, different from case A and case B he carried out "Maneuvering" for speed reduction. And next, different from other 4 cases, operator carried out insufficient "Extraordinary Reaction ".

　

 Thus Behavior in extraordinary situation was classified into 3 patterns. These behaviour patterns agree, with how much the operator achieves functions of Positioning and Lookout before extraordinary situation.