During eight days of experimentation, the GRACE (NLR Amsterdam) and GECO (DLR Braunschweig) research simulators were hooked up via the Internet. GRACE served as the passenger aircraft or 'cruiser' and GECO served as the tanker aircraft or 'feeder'. During the experiments, 28 professional airline pilots flew different scenarios, in which they not only carried out standard refuelling operations, but also experienced how to ensure that no dangerous situations arose. Examples here included flying in turbulence, an engine failure during refuelling and rapidly deteriorating visibility. The pilots could call off the operation at any point by having the autopilot carry out an abort manoeuvre, ensuring a safe separation distance between cruiser and feeder.
The experiments took place within the context of the European RECREATE (REsearch on a CRuiser Enabled Air Transport Environment) project. Comparable experiments carried out by NLR in 2013 revealed that cockpit instrumentation had to be modified to better provide pilots with information. Based on pilot feedback, the cockpit instruments were improved for the second phase of the experiments.
The cruiser-feeder operations are fully automated, but are constantly monitored by the pilots and can be terminated whenever this is deemed necessary. The pilots all agreed that the safety is guaranteed because they can intervene if necessary, without significantly increasing workload. Under normal conditions, the autopilot ensures completely safe operations.
The research showed that refuelling on long-haul routes can generate significant fuel savings, while reducing CO2 emissions. In addition to contributing its advanced knowledge and facilities, NLR is also in charge of coordinating the RECREATE project, which is subsidised by the European Commission.
The RECREATE project concluded in January 2015 with a two-day meeting where all the project results were discussed. The complete logistics chain for the cruisers, design proposals for the feeders, as well as a detailed design for the fuel transfer link were presented as an integrated solution. A step-by-step plan for acceptance and certification has cleared the way for discussions with aviation authorities to enable air-to-air refuelling.