Why did they have three XXXs - could never work that out? Somewhere over the Alps I assume - great picture.
It is indeed a 29 Sqn F3 en-route to Cyprus.
The story is that back in the WW1 era, the squadron commander told an erk finisher to paint 29 in Roman numerals on the fuselages of the aircraft.
The painter asked what 29 was in Roman numerals, to which the boss said
"XX1X" - so that's exactly what he painted, two Xs on one side of the roundel and the "oneX" on the other.