I was at a B of B air display at St Athan back in the 50's. One of the highlights was meant to be a transonic fly by from a USAF F86. To do this, we were told, he had to climb to a great height and dive into his display.
When he arrived he didn't seem to be going that fast and we were then told that he had done his flyby at RAF Llandough, which was an MU about 8 miles away and by the time he realised, he had slowed down a lot.