Beancounter: thanks for the advice that the flypast was 55 strong - now I know why it looked so good! And for David Parry, a link suggesting that it was Hermes relieving Victorious:
Victorious & Hermes at Aden
In May 67, with final withdrawal from Aden some 6 months off, things were a bit fraught, particularly for families living offbase. If the flypast was intended to be a show of strength, I'm not sure how successful it was. Just a month later came the Aden Police mutiny and a bitter day in Crater for the Northumberland Fusiliers. Some days later, that area was reoccupied by Colin Mitchell and his Argylls, and some of the withdrawal plans were advanced. Nonetheless, the flypast was a tonic on the day.