Over the past two decades the German Aerospace Center facility near Heilbronn, Germany, has conducted a considerable number of tests of the ARIANE-5 main rocket engine. From the 159 studied tests a large portion (~45%) was detected at IMS infrasound station IS26 in the Bavarian forest, located at a distance of about 320 km in an eastward direction (99° clockwise from North). Observations were mostly made during the winter season between October and April with a detection rate of more than 70%, as stratospheric winds then favour atmospheric infrasound propagation within a stratospheric duct. For the summer season the reversal of middle atmospheric wind patterns generally inhibits signal detections, as is found by comparisons of numerical weather prediction models. A significant portion of non-detection cases during winter, however, also exhibit a sound speed profile that should enable infrasound signal observations due to the presence of a stratospheric duct. Using European Centre for Medium-Range Weather Forecast (ECMWF) atmospheric model analysis and infrasound propagation modelling it was found that about two-thirds can be explained by the existence of a shadow zone near the station. For one third of the cases, however, such a shadow zone does not exist and it must be concluded that the applied atmospheric model is more often than expected unable to correctly explain infrasound propagation to regional distances, as has been found in previous studies.