Nick Mason in his book 'Inside Out' wrongly ascribes this incident to the Pittsburgh show of 20 June 1975. Nick says (page 215) when talking about the inflatable pyramid "The first show was in Atlanta, where the strength of the wind was outside our safety parameters and sufficient for the whole thing to fail. We tried hard to remedy the problem by sending the whole rig for repair and redesign during a series of indoor shows, but, bugged by poor weather, the difficulties of transporting the helium,and further high winds, when we got to Pittsburgh two weeks later, we eventually - like Captain Hornblower faced with an out-of-control mainsail - instructed someone to cut the thing free."
As you can see by the cutting above, the incident occurred at the Roosevelt Stadium NJ 15 June 1975.
Eyewitness accounts of the Pittsburgh show describe the weather condions as follows "It was a hot, clear day and a very humid night. A full moon rose over the stadium later in the evening. The pyramid sagged a lot, (it was constantly being pumped up with air compressors), but it never collapsed on that night.
With thanks to Sam Marshall for the graphic.