Initial Target Time Over (TTO) Concept for Amsterdam Airport Schiphol

The rapid growth of demand in recent years has outpaced capacity and this has led to increasing delays at Schiphol. One of the sources of delays is the occurrence of so called ‘traffic bunches’, short periods of over-delivery of traffic, at the boundary of the Amsterdam FIR. Traffic bunches create high workload for the controllers and negatively affect the performance of the arrival management system (AMAN). This in turn leads to low level holding, and extensive vectoring of aircraft. To combat the traffic bunches and balance the demand with capacity, local Air Navigation Service Providers (ANSPs) can request the Network Manager (NM) in Brussels to regulate traffic by imposing Calculated Take-Off Times (CTOTs) on aircraft, which can lead to significant departure delays. However, the effectiveness of imposing CTOTs is limited in combatting traffic bunches: as delays are often made up for by higher cruise speeds and direct routing. Knowing the limitations of so called tactical regulations, ANSPs may be tempted to set more stringent regulations to protect controllers from excessive workload. Tactical regulations and the subsequent network delay, however, are bad for airline punctuality and as they affect connectivity between flights, they are bad for the hub-function. To curb the trend on network delays, SESAR has introduced a new complementary concept known as Target Time Over/Arrival (TTO/TTA). This concept is a step towards a collaborative solution to deal with traffic bunches, without driving up network delays.

The KDC studies into application of the TTA/TTO concept support the future air traffic management concept in which demand and capacity is well balanced. The balancing between demand and runway use is important for Schiphol to respect environmental agreements. The reduction of network delay is important for the connectivity of the airport. Thus the TTO/TTA concept serves multi stakeholder purposes. However, application of the TTO/TTA concept can delay the arrival time of individual flights. Therefore the challenge is to apply the TTA/TTO concept such that it does not negatively affect the connectivity of flights.

Before the TTO/TTA concept can be tested and implemented at Schiphol, it is necessary to properly study the feasibility aspects (how it could fit into the existing operations) and benefit aspects of the concept.

KDC performed two studies into the TTO/TTA concept:

  • The first study is an inventory about the content of a TTA/TTO concept and the relation with other concepts that LVNL is working at (e.g. AMAN, XMAN, SESAR trajectory base operation), performed by the NLR. This study details the SESAR TTA/TTO concept, analyses best-practices of past trials at other airports and ANSPs and uses these best-practices to assess the stakeholder acceptance of an initial TTO concept for the Schiphol. Interesting solutions are the ones that are effective in reducing network delays.
  • The second study is an initial TTO trail, supported by To70. This is a live proof of concept trial performed to quantitatively assess the actual benefits at Schiphol. This trial aims to improve the effectiveness of ATFM regulations (as an enabler to reduce the frequency and severity of regulations). Potential positive results may contribute to capacity improvements in the long term. The objectives of the TTO trial are: to demonstrate effects on the distribution of flights in the EHAM FIR using the TTO provided by NM in slot messages and CTOT, to demonstrate feasibility of the concept for flights crews and the validity of the concept using data analysis.

The work on TTO/TTA is by no means finished. The KDC expects future development steps before the concept can be introduced at Schiphol airport.


The results and TTO concept of the first study by the NLR can be read in the full report.


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