MADRID, Aug 4 (Reuters) - Rolls-Royce is preparing to sell its ITP Aero unit to U.S. private equity firm Bain Capital and Spanish engineering group Sener for 1.6 billion euros ($1.90 billion), Spanish paper Expansion said on Wednesday, citing financial sources. The newspaper said both the Spanish government and authorities in the Basque region where ITP Aero is based looked favourably on a sale to Bain and Sener. Sky News had previously reported that rival Spanish aerospace group Aciturri was planning its own bid. $1 = 0.8409 euros Reporting by Nathan Allen; Editing by Alison Williams Our Standards: The Thomson Reuters Trust Principles.