Runway Pressure Research: The effect of en-route delay absorption on the runway throughput

Major airports in Europe experience a number of arrivals close to the maximum of their capacity throughout the day. Multiple aircraft arrive at the airport in a short time window and often have to be delayed in the airspace surrounding the airport before they are cleared to land. A higher fuel burn and costs for the airlines is the result, but it also has a negative effect on the environment in terms of additional pollution and noise. The Cross-border Arrival Management (XMAN) project, which is part of the Single European Sky program, tries to reduce the negative effects of delay in the proximity of airports. The main idea is to shift the necessary delay in the Terminal Manoeuvring Area (TMA) or holding towards the cruise flight phase by reducing the speed of aircraft. If an aircraft is inbound for an airport and the expected arrival time is too close to the arrival time of a leading aircraft, the trailing aircraft can be asked to slow down such that it arrives at the airport when the runway is available. The speed reduction or gaining additional flight time is referred to as ‘delay absorption’. Although the shift of delay absorption from the TMA to the en-route phase shows promising results for fuel consumption and reduced emissions, the question rises whether this En-Route Delay Absorption (ERDA) can also have a negative impact on the runway efficiency. If aircraft are delayed too much in an earlier flight phase due to e.g. inaccuracy of the expected arrival times, so called gaps appear in the landing sequence. As a result, the total number of aircraft that actually landed per time period decreases. The idea is that in order to maintain an optimal runway throughput, some expected delay should be left in the TMA for the approach controller to absorb. In that case, the approach controller can fine-tune a tight landing sequence without any gaps that would result in an underused runway when the demand for landings is high. This phenomenon is defined as Runway Pressure. The main goal of this research project is to investigate the effect on the runway throughput when the expected delay is absorbed in the en-route phase. To achieve this goal, different fast time simulations are performed with a model of both Schiphol and Charles de Gaulle airport. The amount of expected delay that needs to be absorbed in an earlier flight phase is calculated in analogy with the working principles of the inbound planning system of both Schiphol and Charles de Gaulle airport. The expected arrival time at the runway is given for an aircraft and compared with the expected arrival time and minimum required separation time of the previous aircraft in the inbound planning. If the trailing aircraft is expected to arrive too soon at the runway, it has to be delayed prior to passing the Initial Approach Fix (IAF). How the aircraft is delayed, is not researched in this project. However, a maximum of five minutes delay absorption in an earlier flight phase is set, based on previous research on this topic. One simulation scenario consists of a period of two hours where the amount of demand for arrivals changes throughout the inbound peak. The demand exceeds the maximum runway capacity for a certain period of time in each arrival peak. The landing sequence order does not change. A comparison is made between scenarios with the same amount of demand throughout the inbound peak, but with all aircraft either experience En-Route Delay Absorption or not. The outcome of the simulations is the average amount of delay in the ? per 20 minutes and the amount of landings per rolling hour. A rolling hour consists of three consecutive time periods of 20 minutes. Based on the simulation outcomes, it can be concluded that ERDA can result in a small decrease of runway throughput, with a maximum of one aircraft per rolling hour. However, a decrease does not always occur. By the end of the inbound peak, the actual landing time of an aircraft with ERDA is between 30 and 90 seconds later than the same aircraft with no ERDA. So the inbound peak is extended in time and shifted backwards with approximately one extra landing when ERDA is applied. The benefit is that aircraft have to spend up to four minutes less in the TMA. An important parameter that determines the runway throughput, is the inter-arrival separation. This separation between different aircraft wake vortex categories is translated from distance to a time based separation. The same time interval at the threshold is used for the interval times between aircraft passing the IAF. The required passing time at the IAF can be calculated by one average flight time for each aircraft category, where a distinction has to be made between the flight time of jet and turboprop engine aircraft. If the total flight time in the TMA between aircraft categories deviates more than one minute, it can be necessary to use different approach paths to the final approach fix for each aircraft category, in order to maintain safety and a sufficient runway throughput. It is important that the calculations of the inter-arrival times at the threshold and IAF are as accurate as possible. If the inter-arrival time for each aircraft is wrongly increased by five to ten seconds, the throughput decreases with two landings per hour. It is meaningful to take this into account when a dynamic time based separation for the threshold is calculated and compensated for strong headwinds. The definition of runway pressure suggests that there is a minimum amount of delay that should be left for the approach controller to absorb, in order to guarantee sufficient runway throughput. From the results of this research, it can be concluded that there will always be a minimum amount of delay that needs to be absorbed in the TMA to optimize the landing sequence. However, the minimum amount of delay in the TMA is a consequence of the difference in flight time between aircraft types and the accuracy of the actual time passing the IAF. If the inter-arrival times at the IAF are set correctly, a minimum amount of delay is not required to maintain sufficient runway throughput. Although a minimum amount of delay in the TMA is not required to maintain runway throughput, not all delay can always be absorbed in earlier flight phases. Therefore, it is recommended to investigate the effect on the workload of air traffic controllers and the delay absorption capacity of the different airspace sectors along the route. If the expected delay is divided and absorbed in the different flight phases along the trajectory towards the airport, the arrival process is easier to manage for all controllers involved.