original_query: What is the reason behind Qantas' decision to retire its entire 747 fleet, including all 747-400ERs, by 2020?
query: What is the reason behind Qantas' decision to retire its entire 747 fleet, including all 747-400ERs, by 2020?
answer: While the text mentions Qantas' retirement of its 747 fleet by 2020, it does not explicitly state the reason.  The article focuses more on the technical aspects and history of the 747-400.