Rolls-Royce dropped out of the race to power Boeing's planned mid-market aircraft Thursday, saying it did not want to risk more disruption for its airline customers by rushing out a product without extensive testing. The move strengthens a leading position in the high-profile contest already held by a transatlantic venture involving Rolls' arch-rival General Electric, industry sources said, Rolls-Royce wants to avoid a repeat of the problems with its Trent 1000 engine that powers Boeing's Dreamliner 787. CE Warren East said he had taken the "very difficult decision" to withdraw from the Boeing competition because it couldn't make the development of its new UltraFan architecture fit the timetable for the aircraft. <br/>