The cause for the crash of Viasa Flight 897 was never determined by either Portuguese or Dutch authorities . The official report out of Portugal concluded " Notwithstanding a very thorough , time-consuming investigation , in which many authorities and experts co-operated , it was not possible to establish a probable cause of the accident . " The Netherlands , as state of registry for the aircraft , commented : " Though there are no direct indications in this respect , the Board regards it as possible that the accident was due to the pilot or pilots being misled by instrument failure , in particular of the artificial horizon , or to the pilot having been distracted , so that a serious deviation from the normal flight path was not discovered in time . " At the time it occurred , Flight 897 was the third fatal crash of a big jetliner since they were introduced into service in 1958 . It was the worst civilian aviation incident ever to take place in Portugal until the crash of TAP Air Portugal Flight 425 in 1977
TAP Air Portugal Flight 425
TAP Air Portugal Flight 425
Viasa Flight 897