Intra was bought from its founders by a UK based businessman in the mid '70s. After achieving considerable notoriety in 1978/79 involving amongst other things Police raids on the companys offices & appearances by some company management & employees in the Jersey Police Court the Airline was bought by Fields Aviation who at that time owned what was then known as Express Air Freight (now Channel Express). For the summer of 1980 Express operated passenger services using one of Intras Viscounts & two of their own Heralds. The Viscount was painted in JEA Coulours as part of a joint operation with JEA.
JEA itself was formed in late 1979 as i believe an offshoot of Aviation Beauport initially operating one Islander on some former Intra routes. By the summer of 1980 they were operating Bandeirantes & Twin Otters as well.
So in fact in 1980 There were two Airlines flying passenger services under the Jersey European banner!