I don't have full details but Aer Lingus was eager to lease out one of its 747s once the 1970s oil crisis hit and the type was really too big for the carrier's needs. Even though a third (ex-LH) machine was added as noted above, the carrier still preferred to lease out one of the fleet where possible. Even then the utilisation rates of the remaining two 747s were not anything like today's levels. The Alitalia lease mentioned was quite short and to cover for maintenance, IIRC. The Aer Lingus leasing operations had their origins in the highly seasonal nature of the carrier's operations and consequent benefit if a number of aircraft could be leased out during the winter period. One of those most involved was Tony Ryan, who went on to be one of the founders of GPA and later, of course, Ryanair.