A friend who was in the Mall for the flypast noticed that in contrast to other flypasts that he had seen, this one did not fly straight down the Mall, but was offset to one side. He would like to know if this was deliberate (safety or security considerations ?) or whether somebody just got lined up wrong

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Does anybody know why this might have been, or can enlighten us on how these flypasts are lined up ?
He says that there was a noticeable air of dissapointment that the flypast didn't actually go overhead
Thanks for your time.