1947 BSAA Avro Lancastrian Star Dust accident

On 2 August 1947, Star Dust, a British South American Airways Avro Lancastrian airliner on a flight from Buenos Aires, Argentina, to Santiago, Chile, crashed into Mount Tupungato in the Argentine Andes. An extensive search operation failed to locate the wreckage, despite covering the area of the crash site. The fate of the aircraft and its occupants remained unknown for over fifty years, giving rise to various conspiracy theories about its disappearance.

In the late 1990s, pieces of wreckage from the missing aircraft began to emerge from the glacial ice. It is now believed that the crew became confused as to their exact location while flying at high altitudes through the jet stream. Mistakenly believing they had already cleared the mountain tops, they started their descent when they were in fact still behind cloud-covered peaks. Star Dust crashed into Mount Tupungato, killing all aboard and burying itself in snow and ice.

Source: Wikipedia