The delays are so severe that one customer, South Africa, got tired of waiting and cancelled its order for eight planes.
Officials and politicians applauded as the A400M left the runway in Seville at the start of its three-hour maiden flight.
The plane was designed to replace ageing military cargo carriers in several European air forces.
But amid growing concern, French and German officials have given the firm until the end of the year to prove that the project remains viable.
There is a split between those countries who want the aircraft built and in use quickly, such as the UK and France, and those who would prefer to proceed more slowly to spread the cost, such as Germany.
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