When substantial crosswinds are present, aircraft can take-off in quicker succession. But how quickly? NLR researched this question as part of the recently completed European project, CREDOS.
Research conducted during the CREDOS project revealed that when there is sufficient crosswind, aircraft can have shorter delays between take-offs. CREDOS stands for Crosswind Reduced Separations for Departure Operations. Eleven European organisations, including Airbus, Eurocontrol and FAA, have been collaborating in the CREDOS project since 2006, with the aim of studying the effects and potentialities of crosswind. The objective: more efficient departure times, which will improve the punctuality of airport departure schedules and help minimise future flight delays.
Due to the rotating wake vortices that aircraft leave behind when taking off, aircraft cannot takeoff in quick succession. These rotating wake vortices are potentially dangerous, as they can cause an aircraft flying into the wake to lose control. In order to ensure safe takeoffs, international ICAO standards have been agreed, stating that there must be a delay of at least two minutes between takeoffs. This time period is however dependent on various factors, including the speed and size of the successively departing aircraft (the heavier the aircraft, the bigger the wake) and weather conditions.
Within the CREDOS project, NLR is responsible for the new operational concept for taking off in crosswinds and for validating this concept. NLR tested the concept with real-time simulations in its Narsim flight simulator, where researchers witnessed for the first time that the concept works. NLR-Air Transport Safety Institute (NLR-ATSI) carried out the safety studies required for this new flight concept. NLR-ATSI, together with Airbus and DLR, studied the risks and odds of an aircraft entering rotating wake vortices, and what the consequences of this would be. The work of the air traffic controller and Eurocontrol were also studied. What happens for instance if under various crosswind conditions an air traffic controller gives take-off clearance after 90 seconds, rather than the standard two minutes? What consequences would this have for the next departing aircraft? In addition, NLR is involved in the creation of a database of turbulence data based on onboard flight information.
CREDOS has shown that for example when a crosswind of 7 knots (approximately 3.5 metres per second) is present, aircraft can take off 30 to 60 seconds earlier. But before this can be implemented, and aircraft – aided by crosswinds , are able to depart with shorter time delays between each takeoff, the CREDOS concept must be tested at airports, which is a next step planned for 2012 as part of the EU’s SESAR project (Single European Sky ATM Research).