A parent unit is provided having: a precedent base for accumulating data from child units; an element data determination unit for processing the data into element data; an element data classification unit for creating a classification; an element data change classification unit for determining which classification the element data belongs to, and calculates transition probabilities among the classifications, and a display unit for displaying data. The child unit collects air current data, processes the data, obtains the transition probabilities, and calculates a probability of encountering air turbulence. The child unit then displays certain data when the probability of encountering air turbulence satisfies predetermined conditions.