A flight monitoring system comprises a first set of flight-status detecting sensors comprising a first-type sensor A1 for providing a first-type measurement result and a second-type sensor A2 for providing a second-type measurement result; a second set of flight-status detecting sensors comprising a first-type sensor B1 for providing a first-type measurement result and a second-type sensor B2 for providing a second-type measurement result. The flight monitoring system further comprises a control module configured to perform: comparing a difference between the first-type measurement results from the first-type sensors A1 and B1 with a first predetermined threshold; if the difference is more than the first predetermined threshold, deciding a first-type sensor data of the first-type sensors as indefinite; and determining a value of the first-type sensor data by selecting one of the first-type measurement results from the first-type sensors A1 and B1 as the value of the first-type sensor data according to the second-type measurement results, and setting the first-type sensor data as definite after the selection.