Osoaviakhim-1

Osoaviakhim-1 was a record-setting, hydrogen-filled Soviet high-altitude balloon designed to seat a crew of three and perform scientific studies of the Earth's stratosphere. On January 30, 1934, on its maiden flight which lasted over 7 hours, the balloon reached an altitude of 22,000 metres (72,000 ft). During the descent the balloon lost its buoyancy and plunged into an uncontrolled fall, disintegrating in the lower atmosphere. The three crew members, probably incapacitated by high g-forces in a rapidly rotating gondola, failed to bail out and were killed by a high-speed ground impact.

According to public investigation reports, the crash was ultimately caused by a prolonged stay at record altitudes exceeding maximum design limits. The balloon, overheated by sunlight, lost too much lifting gas in the upper atmosphere. As it descended past the 12,000 metres (39,000 ft) mark, cooling down to ambient air temperature, quick loss of buoyancy caused downward acceleration that triggered structural failure of the suspension cables. The aircraft design was marked by numerous engineering flaws, notably insufficient ballast weight and faulty gondola suspension design, which all contributed to the loss of life.