This is a pilot's joke: they are over the Golden Ball which is a prominent landmark atop St Lawrence's Church, West Wycombe, for pilots heading into Booker (Wycombe Air Park). Where you wouldn't try to land a Lancaster unless you had three engines out! In the summer of 2014 the only two remaining airworthy Avro Lancasters - normally separated by the Atlantic Ocean - flew together for the first time. The Canadian Warplane Heritage Museum's Mynarski Memorial Lancaster FM213, flying in the markings of KB726 VR-A of RCAF No 419 (Moose) Squadron, crossed the pond to join the RAF Battle of Britain Memorial Flight's Lancaster PA474, in the colours of DV385 KC-A, "Thumper Mk III" of 617 ('Dambuster') Squadron.