MADRID/PARIS, March 13 (Reuters) - Doubts are growing over the future of Madrid's remaining orders for the Airbus (AIR.PA) A400M troop plane, European defence sources said on Monday, as corporate leaders and dignitaries marked the centenary of Spain's military planemaking activities. Prime Minister Pedro Sanchez, Defence Minister Margarita Robles and King Felipe also attended Monday's event. Spain and Airbus are in discussions over how to soften any impact from a partial A400M order cancellation, sources said. Defence publication Janes reported last year that Airbus was waiting for Madrid to back the SIRTAP tactical drone project, co-developed by Airbus Spain and Colombia. Spain also last year ordered an extra 20 Eurofighter combat jets, a four-nation fighter programmre for which Airbus is the industrial partner in Spain and Germany.

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