Crosswind - Reduced Separations for Departure Operations (CREDOS)

As an answer to the rising numbers of flights and issues of how to deal with the traffic and delays that this may cause we launched CREDOS, a research Project of the 6th Framework Programme of the European Commission in cooperation with 11 partners including universities, national research centres and industry partners in close cooperation with the FAA and NASA.

The research was based on the minimal separation required between aircraft during landing or taking-off. This separation is vital due to wake vortex turbulence – a dangerous air-flow phenomenon. CREDOS’ aim was to study it and update the rules, first set in the 1970s, on how large this separation should be, taking into consideration a wider range of factors such as wake vortex behaviour and meteorological conditions.

The basic premise was to change from separations based on a worst-case scenario to separations derived from knowledge of the probable position and strength of the wake turbulence. The project increased the knowledge of the effects of wake turbulence during the initial climb phase of flights and how crosswind conditions affected this phenomenon. It also developed and demonstrated a concept of operation allowing reduced separations for single runway departures.

By spacing aircraft more accurately, CREDOS contributes to air transport safety and efficiency. It increases airport capacity without extending existing infrastructure. It also reduces delays and helps to accommodate higher traffic demand. This project has also helped raise awareness on the issue and increase its understanding by aviation experts.

CREDOS ended in 2009, giving way to other projects such as:

  • RECAT-EU, which safely increases airport capacity by redefining wake turbulence categories and their associated separation minima;
  • Pair-Wise Separation, which developed a static separation matrix of distance and time for both arrivals and departures
  • Dynamic Pair-Wise Separation, which allows for the dynamic adjustment of aircraft spacing, using wake turbulence measurement, real-time weather conditions and data from air and ground systems;
  • Time Based Separation, which developed new methods for separating arriving aircraft by time instead of applying distance separations in strong headwind conditions;
  • Weather Dependant Separation, which optimises aircraft spacing by taking into account all meteorological conditions (crosswinds, headwinds, turbulence and temperature) and wake vortex behaviour.


The project was structured in 5 Work Packages (WPs):

WP1 on Data Collection Departure wake vortex and meteorological data from St. Louis (KSTL) and Frankfurt (EDDF) was collected covering the full range of seasonal operating conditions.

Download WP1 Deliverables

WP2 on Data Analysis and Wake Vortex Behaviour Modelling Analysis An analysis on departing aircraft under various atmospheric conditions was undertaken and existing models of wake turbulence behaviour was updated to include the departure situation. Download WP2 Deliverables
WP3 on Risk Modelling and Risk Assessment Wake turbulence encounter probability and encounter severity was assessed through risk analysis taking into account a broad range of variables through Monte Carlo simulation and aerodynamic models. Download WP3 Deliverables

WP4 on Operational Concept and Validation

A new concept of operations for crosswind departures was defined and validated. Download WP4 Deliverables
WP5 on Stakeholder Communications and Marketing A comprehensive communication package for ANSPs, Airports and Airline Operators was developed, based on a case study of the virtual implementation of CREDOS at Madrid airport. Download WP5 Deliverables


  • Deutsches Zentrum für Luft- und Raumfahrt (DLR)
  • Airbus Deutschland GmbH (AD)
  • National Lucht- en Ruimtevaartlaboratorium (NLR)
  • M3 Systems (M3S)
  • Office National d'Etudes et de Recherches Aérospatiales (ONERA)
  • Université Catholique de Louvain (UCL)
  • Technische Universität Berlin (TUB)
  • National Air Traffic Services (NATS) (En Route) PLC
  • DFS Deutsche Flugsicherung GMBH (DFS)
  • Ingeniería y Economía del Transporte S.A. (INECO)

Airport Research Support Team

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