NOWADAYS, airlines are required to implement a safety management system (SMS), which quantifies and regulates the current situation in terms of airline safety. One part of the SMS is the so-called flight data monitoring (FDM) or safety data analysis [1]. During flight, civil aircraft record data by a device called a quick access recorder (QAR) as a discrete time series. The number of variables depends on the aircraft type and lies between 500 and 2500 variables. The sampling rate of the recording usually lies between 0.25 and 16 Hz and depends on the variable. The most safety critical period of a civil aircraft flight is the landing [2]. Runway overrun, hard landing, and tail strike are landing accident categories that are of high interest to airlines, aviation authorities, and regulators. Therefore, the approach and landing period are the subject of many safety investigations. For these investigations, the precise trajectory of the aircraft is essential. However, recorded data always contain errors and uncertainties. To improve the quality of the recorded aircraft trajectory, a process to reconstruct the aircraft trajectory was developed at the Institute of Flight System Dynamics and is described in this Note. Not only the recorded position of the aircraft is used but also further data that contain information about the location, such as instrument landing system (ILS) deviations [3]. Another example of data that can be incorporated into the trajectory reconstruction is the data from the radio altimeter (RA).