This is an interview that aired on RTÉ (Irish state television) in 1966.
The pilot is pretty matter-of-fact in his telling and makes a point of ruling out a weather balloon or regular aircraft. The article states that the captain has been with the airline for several years and prior to that he had flown with the RAF.
The co-pilot also witnessed the unidentified craft which was reportedly flying between 600 and 700mph.
https://www.rte.ie/archives/2017/0518/876182-pilot-sees-unidentified-flying-object/
by Hobbesinorbit