Wikipedia's article for the Danube Tower (
visit link) informs us:
"Ballooning accident in 1968[edit]
At a meeting of Pro Juventute on 6 June 1968, four gas balloons were launched from a meadow at Donauturm. While three of them floated past the tower, the fourth was driven against the tower, where it was initially hung on the security grills, at an height of approx. 150 m. The balloon net tore and the balloon envelope broke free. The remnants of the net and the basket fell to the ground. The American balloonist Francis Shields died, along with two Austrian passengers: a higher official of the Austrian Post and Telegraph Management, Guntram Pammer, and journalist Dieter Kasper of the Austrian Press agency."