To prepare for a research flight takes quite some time and involves many people. It starts in general 3-4 days in advance when some scientist sit together over the forecasts and think about the most interesting atmospheric situations to probe. Two days in advance they hand over a preliminary flight plan to the HALO flight operations team. These colleagues from the German Aerospace Center (DLR) talk to Air Traffic Control (ATC). A day in advance this preliminary flight plan is updated with the recent forecast.