This report is the third in a series developed within the Human Error in ATM (HERA) Project dealing with how human errors in Air Traffic Management (ATM) can be analysed to improve safety and efficiency in European ATM operations. The purpose of this work is to increase the effectiveness of error recording, analysis and prevention. This report describes the results of two validating exercise using the HERA-JANUS Technique (see EATMP, 2003).