Analyzing Required Time of Arrival Performance to Low Altitude Meter Fixes

The application of Required Time of Arrival (RTA) control has been a feature in a number of commercial flight management systems (FMSs) since the mid-1980s. RTA operations have become an increasingly important part of the 4-Dimensional Trajectory-Based Operations (4D-TBO) concept. Functionally it can reduce both pilot and air traffic controller workload, increase adherence of aircraft to meet assigned schedules and lead a chain of aircraft such as in Flight Interval Management operations to help a series of aircraft meet their assigned schedule and spacing goals. An outstanding question addressed in this work is what is the expected performance of aircraft conducting RTAs as a function of the crossing altitude of the assigned control point (meter fix), as well as the accuracy and extent of the wind information supplied to the automation and the characteristics of the approach procedure. In this study, 101 actual flights were replicated each across 16 different test conditions within a sophisticated simulation infrastructure which allowed these elements to be varied in order to analyze their impact on RTA performance for a simulated B757-200 aircraft and Flight Management System. It was found that the greatest factor on RTA performance is RTA fix crossing altitude. Greater than 95% of flights had RTA errors of less than ±10 seconds when meter fix crossing altitudes were between 7,000 and 35,000 feet Above Ground Level (AGL) and flying approach procedures with speed constraints regardless of the wind forecast error. That value increased to 100% for flights that had their speed constraints removed from their routes. For flights with meter fix crossing altitudes occurring between 3,000 and 7,000 feet AGL, 76% to 85% crossed with less than ±10 second RTA error depending on the descent forecast used and the presence or absence of speed constraints. It was also found that larger forecast errors increase the probability of larger RTA errors.