Thanks for the info Tassie! I wonder if the missing jet was in memory of the Queen.

The missing man formation is an aerial salute performed as part of a flypast of aircraft at a funeral or memorial event, typically in memory of a fallen pilot, a well-known military service member or veteran, or a well-known political figure.[1][2][3] The planes fly in a formation that leaves a space where one plane should be, symbolizing the person's absence.