Abstract: Two accumulative error indices are defined as the discernment signals of the fault detection in a liquid propellant rocket engine.The biases of the fault detection are selected by way of the interval estimations of the discernment signals,and the operation conditions of the rocket engine are monitored on the basis of the biases derived from the interval estimations.Moreover,the maximum optimal questions of the fault isolation thresholds are considered with the aid of the probability density function for the discernment signals of the fault isolation.The data analysis of the test firings in a large turbo-pump fed liquid rocket engine demostrates that the estimation techniques of confidence interval can improve fault detection time compared to the current engine redline monitoring system.In the detection of anomalous test firings,both of the accumulative error indices correctly detected all faults.In the detection of normal ones,no false alarms were indicated by the first accumulative error index,while only one false alarm was indicated by the second accumulative error index.