The Airbus A400M Military Transport Plane will make its maiden flight in Southern Spain tomorrow, and its success could be critical to a project that is under threat after nearly two years of delays and cost overruns.
The first flight will take place in Seville, a spokesman for parent company EADS said.
Seven European buyer nations are in talks with EADS over whether to save the 20 billion euro ($29.6 billion) defence programme, and defence analysts have said a successful debut would give the project a boost.
Airbus had said it aimed to fly the plane by year-end, which is also the deadline for a political agreement on its future.
The A400M was designed to carry up to 37 tonnes of troops and heavy equipment such as helicopters and armoured vehicles to war zones such as Afghanistan or to support humanitarian missions.
Manufacturers say that if they get the go-ahead to continue production, deliveries can start three years after the maiden flight, compared with an original first delivery target of 2009.
Defence sources say the two sides are discussing a deal that could lift the prospect of penalties and ease strains on EADS without necessarily calling on taxpayers for new funds in the near future, something buyers have ruled out amid recession.
Germany, which ordered 60 of the planes, has however expressed reluctance about allowing any contract changes.
Its deputy defence minister Christian Schmidt said on Wednesday it still needed all the planes it had ordered and had not received any additional financial requests from EADS.
Airbus is due to build 180 of the propeller-driven transport planes for Britain, France, Germany, Spain, Belgium, Luxembourg and Turkey. South Africa cancelled an order for eight last month but Malaysia is so far sticking with an export order for four planes.
The A400M would give Europe its own heavyweight transport fleet and aim for a niche in export markets between the smaller Lockheed Martin C-130 Hercules and the Boeing C-17 jet-powered transport plane, which can carry 75 tonnes.
US defence giant Lockheed has said delays in developing the A400M could boost sales of its own aircraft.